Optical Sensing, Lighting, and Energy
A major fraction of all information received and analyzed by humans is received through the eyes, whether from reading a newspaper, watching television, or just observing our environment. The ability to optically sense and obtain information in this way is fundamental to our human existence and involves the traditional optical science and technology of the human eye, the vision process, corrective eyeglasses or contact lenses, and the use of lighting to permit the surroundings to be illuminated. Although advances have been made in some of these areas, for the most part the fundamental way we observe and see our immediate surroundings has not changed significantly over the past hundred years, with the exception that now artificial lenses and surgical techniques can improve some vision problems and better eyeglasses and corrective procedures are available.
What is significant, however, is the tremendous advance that has occurred recently in the development and use of new optical and infrared sensors and instruments that can detect and analyze our surroundings and present this information to us visually, thus greatly augmenting our normal visual process and in some cases showing details and information never previously seen. For example, a broad range of newly developed optical sensors and instruments are already used in everyday life, such as those that provide satellite pictures of clouds and weather patterns on TV evening news, infrared night vision scopes used by law enforcement, spaceborne probes to Jupiter that use optical instruments to measure and image the surface temperature of the planet, home security infrared motion sensors, and optical or laser probes to detect and display gas emissions from automobile highway traffic. Related to these advances in optical sensing and imaging technology are associated advances in the development of new, high-efficiency
sources of light to illuminate our surroundings and in the use of optics and lasers for development of new energy sources. For example, new lighting sources are being developed that may reduce U.S. energy consumption by tens of billions of dollars per year, and new laser-based nuclear fusion power plants and mass-produced photovoltaic solar cells are being studied for long-range potential as cheap power in the next century.
This chapter presents a synopsis of recent advances in optical sensing instruments and techniques, lighting, and energy. The emphasis is on new or revolutionary optical technologies that are expected to significantly impact the future growth and well-being of our society. As such, technical areas of lighting, energy, and optical sensors that either are mature or are not expected to grow dramatically are not covered in as much depth. Although the topics include a rather broad range of optical fields, they are centered primarily on the generation of light (new lighting sources), the conversion of light to energy (solar cells and laser fusion research), and the use of optical and imaging sensors for the measurement and detection of a wide range of physical and chemical parameters (night vision scopes, video cameras, gas vapor sensors, traffic laser radars, bar-code scanners). The topics covered have been divided into four subsections: (1) optical sensors and imaging systems, with application in the environment, global imaging, astronomy, industrial/chemical sensing, video cameras, law enforcement and security, common optical sensors, and scanners; (2) lighting, including new light sources, light-emitting diodes (LEDs), and the use of lasers in entertainment; (3) applications of optics and lighting in transportation, including autos and aircraft; and (4) energy applications, including laser fusion, laser isotope separation, and solar cells. The role that advances in materials have played in many of these fields is also addressed, because the development of new optical materials is often the key factor enabling progress (Box 3.1).
Overall, this study finds that the areas of optical sensing, lighting, and energy account for sales, research, and development of about $19 billion per year in the United States. This figure includes about $3.5 billion for optical sensors and imaging instruments, $12 billion for lighting fixtures and lamps, $400 million for light-related energy research and solar cell production, and $2 billion for the use of optics in cars and airplanes. The total world market is estimated to be two to three times as large. Some of these applications have a great impact on other markets and represent key or enabling technologies. For example, the efficiency of lamps has a direct impact on the $40 billion that is spent each year in the United States on electricity for lighting. As such, a 50% change in lighting efficiency can have a $20 billion impact on the U.S. economy and an even larger impact on worldwide energy demand,
BOX 3.1 DEVELOPMENT OF NEW MATERIALS
The development of new optical and semiconductor materials has been a key factor in the recent advances made in optical detector arrays, optical biosensors, digital cameras, lighting sources, and solar cell efficiency.
especially in developing countries where lighting and energy production are still expanding. Another example is the real-time global mapping supplied by space-based optical imaging weather satellites. These maps affect a much larger market for weather and crop forecasts and help authorities develop forecasts and emergency plans for storms and hurricanes whose impact in dollars and lives saved is often incalculable. Where practical, these secondary impacts of optics applications are also covered in this chapter.
The discussion of each subtopic is based on the results of a workshop held by the committee, as well as on additional written inputs obtained by the committee. The main findings and conclusions, which cover key highlights and challenges, are collected at the end of each major section. Finally, recommendations based on the findings and conclusions are made to the government, academia, and industry, where appropriate.
Optical Sensors and Imaging Systems
Light reflected from objects has been used by humans for thousands of years as a way to see or remotely sense the presence and composition of the surrounding environment. In most cases, the reflected or transmitted light is seen directly by the eye, and differences in color or intensity over the visible wavelength spectrum are used to detect and differentiate objects and images. Although outside the portion of the spectrum that is visible to the eye, light at ultraviolet (UV) and infrared (IR) wavelengths contains additional information. For instance, absorption and possibly fluorescence at UV and IR wavelengths can be used to detect certain chemicals and pollutant gases, to see objects at night by using IR thermal radiation, and to measure the temperature and composition of a distant object. It is the spectroscopic or wavelength (color) dependent nature of the reflected or transmitted light that allows one to detect a particular feature or the presence of a particular chemical.
The use of optical sensors and imaging systems has been enhanced recently with the advent of small, inexpensive video cameras and detectors that operate in both the visible and the infrared; the development of new compact tunable laser sources; and the manufacture of compact
optical spectrometer instruments. Although spectroscopic optical instruments have been used for the past hundred years, recent advances in these optical techniques and the reduction in their costs have led to the recent surge in their use in a wide variety of fields. The following sections outline the current use and projected growth of optical sensors in environmental and atmospheric monitoring; Earth and global surface monitoring; astronomy and planetary probes; industrial chemical sensors; imaging detectors and video cameras; law enforcement and security; and common everyday optical sensors, printers, and scanners.
Environmental and Atmospheric Monitoring
Optical systems can be used for the detection of a number of important gases or pollutants in the atmosphere. In many cases, each chemical has a distinct absorption spectrum in which different wavelengths (or colors) of a transmitted optical beam are preferentially absorbed according to the concentration and presence of the chemical or gas in the atmosphere. Several different optical techniques are used, depending on the substance of interest, its concentration, and the detection range expected from the instrument. An important point is that optical sensing can often be accomplished remotely, because the optical beam can be directed at a distant object and information about the composition and gases surrounding the distant scene can be deduced from backscattered light. In fact, optical remote sensing can be used to detect chemicals (or physical parameters such as speed and dust cloud density) at ranges from a few meters to several hundred kilometers in some cases. This capability has significantly changed the way we measure our environment. For instance, 30 years ago weather balloons were used to carry instruments aloft to sample the upper atmosphere; now, we use laser beams from the ground to make the same measurements. Similarly, where once we measured the severity of air pollution in Los Angeles by measuring the time it took a stretched rubber band to rot, we now use chemical and optical absorption instruments to obtain round-the-clock coverage of the concentration of ozone and other environmental gases. The advances in these areas are covered in the following sections.
Open-Path Gas Monitoring
Optical gas monitoring uses a beam of light that is transmitted through the open air or through a sample chamber (cell). The beams of open-air systems can cover paths of several hundred meters to several kilometers. Selective absorption of the light allows for detection of the compounds present and quantification of their concentrations. This is usually done by using a conventional optical spectrograph or a Fourier-transform infrared (FTIR) optical spectrometer that directs an
optical beam through the atmosphere by means of a telescope. These optical instruments can be used as sensitive real-time monitors of the composition and concentration of environmental gases in the atmosphere or in a plume from a smokestack. They have been used to detect the concentration of organics, refrigerants, carbon monoxide (CO), nitrogen oxides (NOx), ozone, and other gases in the environment and from industrial sources; to sense emission gases from automobiles over a highway; and to detect evidence of the manufacturing of chemical, biological, or nuclear materials. For example, Figure 3.1 shows an FTIR instrument used to monitor the perimeter of an industrial chemical plant to detect the accidental release of a hazardous gas by the plant. Although conventional analytical chemical techniques such as wet chemical analysis or gas chromatography are often used for this purpose, they do not offer real-time remote sensing or on-site capability as easily as optical monitoring does. The advantage of conventional chemical measurements is the longer historical use of these techniques and their lower capital cost, although their operational costs can be higher. Conventional analytical chemical sensors are still dominant, but optical methods now claim about 40% of the market and this fraction is rapidly growing. The current annual U.S. market for optical instruments used in this area is about $500 million (systems cost). The demand is driven by regulatory laws for source ambient air quality usage, although industrial process control is beginning to incorporate these techniques as well. The recent increased acceptance of such optical instruments by the Environmental Protection Agency (EPA) will certainly stimulate their more widespread use. The main technical challenge is for smaller and cheaper laser or optical spectroscopy devices. At present, there is a significant U.S. market, but the market in Europe is somewhat more
advanced. The slower U.S. development is due to the U.S. regulatory agencies' longer acceptance times for new environmental monitoring technology (currently about 5 years or more).
Lidar Remote Sensing
Laser radar (lidar) has been used for more than 25 years to detect from afar a wide range of atmospheric or environmental characteristics, such as temperature, gas concentration, and wind velocity. Lidar uses a laser beam to probe a remote target, aerosol layers, or gas clouds at ranges from 10 m to several kilometers and deduces the range and composition of the cloud or target from the detection of backscattered light. Combined with spectroscopic wavelength control, tunable lidars have detected and mapped ozone, water vapor, methane, and other pollutant gases in the atmosphere or in smokestack plumes. In the effort to understand global climate change, lidars have been used to monitor gas concentrations and temperatures in the upper atmosphere and the concentration of ozone, water vapor, and methane over the Amazon jungle. If their sensitivity is high enough, range-resolved lidar returns can be used to map in three dimensions the physical extent of a plume or haze region; this was done to map the global movement of volcanic ash clouds from the eruptions of Mount St. Helens and Mount Pinatubo. Airborne lidar systems have been used to make range-resolved maps of the density of haze over the Los Angeles basin. Figure 3.2 shows a plume of ozone detected and mapped using a differential-absorption lidar; this ozone plume was found over the mid-Pacific near Tahiti and was part of a smoke plume produced by biomass (trees) burning in Africa and transported thousands of miles by global winds. Also of
importance is the recent use of a airborne range-resolved precision lidar by the National Aeronautics and Space Administration (NASA) to measure the canopy height and depth of foliage to determine the biomass coverage of Earth. This latter use will significantly increase our knowledge of the density of forests and jungle growth in remote sites, which is crucial for accurate predictions and understanding of the production of oxygen and uptake of carbon dioxide (CO2) by plants on Earth.
A potentially significant new application for lidar will be its joint use with an open-path optical spectrometer instrument, since lidar can measure and map cloud or aerosol movements in three dimensions while the open-path instrument can determine the integrated gas concentration. Such measurements would yield gas flux values, which are most vital for environmental and gas emission regulatory detection.
Lidar instruments are still rather expensive and one of a kind; they are used more for research than commercial applications, with government funding for lidar still greater than private or commercial funding. The total U.S. market is on the order of $10 million to $20 million per year, but significant growth is expected as the required laser sources become available in more compact, less expensive forms, especially diode-pumped solid-state lasers and optical parametric oscillator (OPO) lasers. Thus, the growth potential for lidar remains dependent on developments in lasers. One important use now being evaluated is for aircraft wind shear and wake vortex detection at airports. Such a device would be an important enhancement to aircraft safety. Airlines, air cargo companies, and the U.S. Air Force are also interested in the use of on-board lidars for measurement of wind profiles below, above, and ahead of aircraft. Significant fuel savings could result from the use of such data. At present, significant work in this area is being done in Japan and Europe, as well as in the United States.
Another growing lidar market is for police laser radars to detect traffic speeds. The current annual world market for this application is on the order of $10 million to $40 million. Laser devices have the advantage over radar that the small laser beam can select a single automobile from a group of vehicles and can measure the range to the vehicle with an accuracy of better than a few centimeters. The type of traffic lidar shown in Figure 3.3 costs about $4,000, compared with about $1,500 for conventional microwave radar. Several U.S. states now each have several thousands of these lidars in use by local police agencies.
A related instrument, the laser range finder, is used by land surveyors to map distances to an accuracy better than 1 cm and for the detection of Earth's crustal movement (earthquakes) over fault lines or volcanic sites. Since a laser beam is very directional and small, it can be used for the precision determination of angular and distance measurements in both construction and land surveying, where the traditional
transit for survey work essentially has been displaced by an invisible, infrared laser transmitter and a retroreflecting mirror on a pole.
The question of eye safety is always of concern with lidar since the laser beam can be directed toward an urban population in some cases. Usually, this concern is handled by increasing the size of the laser beam transmitted into the atmosphere so that its intensity falls below the allowable eye safety value for direct ocular viewing (i.e., for a beam aimed directly into the eye). This value is about 10 mJ/cm2 per pulse for an IR wavelength greater than about 1.4 microns. For lasers at visible wavelengths, the limit is several orders of magnitude lower, since the eye focuses visible light onto the retina, whereas infrared wavelengths are not focused but absorbed in the cornea and interior portion of the eye.
Optical Environmental Biosensors
A new type of optical biosensor, developed during the past decade, uses the combination of an optically active bioreceptor and a photodetector as an ultrasensitive sensor (Rogers and Gerlach, 1996; Vo Dinh et al., 1994). Biosensor materials change color or other optical properties in the presence of trace amounts of a known chemical or biological substance; they provide excellent specificity and sensitivity for a wide variety of environmental chemicals and biological agents. Most of these optical biosensor materials use an enzyme, DNA, and an antibody-based fluorescence label or other bioreceptor or an optically active bioagent that changes color or fluoresces in the presence of a specific substance. Most place the bioreceptor on the end of a fiber-optic probe or waveguide as the sensing end of the instrument, although some techniques use an optical microcavity with a chemically permeable membrane. These techniques are already being employed in the pharmaceutical and medical laboratory industries in the form of test kits and are used in polymerase chain reaction (PCR) applications as DNA probes. The market for such optical instruments was about $400 million in 1991 and is growing rapidly. Future markets are predicted to be about $1 billion annually for monitoring and bioremediation (making harmless) of hazardous waste dumps and $300 million annually for environmental sensing of water and air quality. Table 3.1 shows a list of some bacteria and viruses that are being detected using DNA-sensitive optical biosensors.
TABLE 3.1 Bacteria and Viruses Detected Using DNA-Sensitive Optical Biosensors
Giardia lamblia bacteria
Work is progressing to make optical biosensors more rugged and cheaper over the next 2 to 3 years, which would greatly expand their utility and commercial use for applications in medicine and public health (e.g., glucose sensors; see Chapter 2). In addition, current research is directed toward producing a complete optical biosensor on a chip, using techniques similar to those used to manufacture silicon integrated circuits.
Earth and Global Surface Monitoring
Optical sensors and television imaging systems based on high-altitude aircraft, balloons, and satellites have been used for more than three decades to detect and map weather patterns, mineral resources, ocean currents, and land topography on Earth's surface. Recently, more sophisticated optical instruments have been used that can detect the concentration of important greenhouse gases related to the study of global climate change. As such, there is both a commercial and a scientific use for high-altitude aircraft (U2), balloon, and satellite-based optical instruments.
Atmospheric and Global Climate Change
Remote sensing from satellites or high-altitude aircraft or balloons is a cost-effective way to obtain homogeneous, global measurements of critically important weather and climate variables such as atmospheric temperature and humidity profiles, cloud properties, stratospheric and tropospheric aerosol amounts, sea surface temperature, ocean color, sea ice coverage, stratospheric and tropospheric ozone, and other important trace gas concentrations. A wide variety of techniques are used, including passive microwave, infrared and visible spectroscopic imaging, solar and lunar occultation, and radar and laser ranging. Of these systems, about half are optics based, including those used for cloud properties, ocean temperature, trace gas measurements, and humidity profiles. For climate monitoring, long-term precision in the measurement of properties is required. Such measurements have been
used to monitor the Antarctic ozone hole and to measure trends in cloudiness, Earth's radiation balance, and air temperature.
Since the first weather satellite was flown in 1960 there has been a continuous program of improvement along with the introduction of techniques to measure new physical variables from space. In the United States, NASA has its Mission to Planet Earth—Earth Observing System (EOS) program to collect a benchmark series of important visible and infrared global climate observations in the late 1990s and the early twenty-first century. The Upper Atmosphere Research Satellite (UARS), placed in Earth orbit earlier this decade, incorporates a wide range of optical spectroscopic instruments to measure freon and ozone-related chemicals in the upper atmosphere.
A vigorous program of innovation is under way to develop smaller, more capable, less expensive instruments. The National Oceanic and Atmospheric Administration (NOAA), the Department of Defense (DOD), and NASA are cooperating in developing the National Polar Orbiting Environmental Satellite System, a more efficient and capable system for operational weather and climate observations from satellites. The European Space Agency (ESA) and the Japanese space agency (NASDA) also have active Earth remote sensing programs for weather and climate research and are developing new tunable-laser lidar and long-path absorption technologies for this purpose.
Earth's Resources and Weather
Earth remote sensing satellites typically have optical or infrared instrumentation included in the satellite sensor package, sometimes in addition to microwave or radar sensors. The optical sensing instruments provide extensive knowledge of the global weather, agricultural resources, and land topography of Earth's surface (Office of Technology Assessment, 1990). Since the 1960s, satellite systems such as the Geostationary Orbital Environmental Satellite (GOES) system have provided near real-time photographs and digital images of clouds and weather patterns. For example, Figure 3.4 shows the image of a hurricane and its associated weather pattern off the coast of Florida in 1996. Since 1972, spectroscopic (or multispectral) wavelength bands in the visible to near-infrared region have also been used to detect agricultural parameters such as plant stress, plant density, and growth rates and to produce resource maps showing the location of minerals and sediment flow in rivers. For example, satellite-based multiwavelength optical imaging sensors have been used to map Earth's green biomass, i.e., plant density.
An estimated $28 billion has been invested in remote sensing satellites that include optical imaging systems (see Figure 3.5). Of this total, a relatively smaller amount, on the order of several hundred million
dollars, represents the actual optical components and instruments used in the satellites. There are currently five operational optical imaging satellites in orbit: SPOT 3, Lansat 5, JERS-1, OFEQ 3, and IRS-2C. The majority of such systems are funded by governments including costs from satellite and downlink station design through deployment. Eight commercial remote sensing systems are scheduled to be launched by the year 2000: EarthWatch, Inc.'s Earlybirds (2) and Quickbirds (2); Space Imaging (1); and Orbital Science Corporation's SeaStar (1) and Resource 21 (2). The U.S. government plans to launch a series of Earth observing sensors starting in 1999. Other countries are planning to deploy an additional 10-15 satellites by 2000. Anticipated (and demanded) lower future launch costs are driving the systems toward lighter and cheaper packages. The trend is therefore toward an increase in the number of commercial satellites at lower costs ($50 million to $100 million each) for all applications, including agricultural and forest remote sensing. Optical systems capable of generating detailed digital elevation models (DEMs) have been identified as one of the biggest markets for this type of data and will be used for the generation of precision land contour and elevation maps for precision farming, watershed flow prediction, and land surveys. U.S. government policy regarding remote sensing data is contained in the Land Remote Sensing Act of 1992 and relates to the market for monitoring information, which is estimated to be on the order of $300 million per year for environmental uses. Approximately $2 billion per year for all applications (including
agricultural uses), has been forecast as potential value in expenditures by investment brokerage (commodities) groups and commercial businesses.
Astronomy and Planetary Probes
Optical sensors, telescopes, and instruments play a vital role in the field of ground- and space-based astronomy and studies of the solar system using spacecraft probes. During the past few decades, significant advances have been made in each of these areas. Although they have, at present, little commercial potential, this important field has significant scientific and societal benefit.
New Astronomical Telescopes
Optical telescopes have been used since the time of Galileo to study and map the heavens. Large telescopes are essentially ''time machines" that peer far back in time toward the early universe. The field of astronomy is being rapidly changed by stunning advances in (1) optical engineering of larger telescopes; (2) techniques that compensate for optical distortions of Earth's atmosphere using "adaptive optics" and laser-excited artificial guide stars in the upper atmosphere; (3) coherent addition of two or more separate interferometric images from separate telescopes to increase the resultant resolution; and (4) the use of new ultrasensitive UV and IR detector arrays and computer-enhanced images. These advances are enabling researchers to actively engage the fundamental questions of astronomy and astrophysics: Are there planets around nearby stars? What is the origin of structure in the universe? What powers the galaxies? What is the nature of cosmic dark matter? Significant progress in answering some of these questions can be
expected in the next few years as a result of recent developments in optical science and engineering.
Several advances have recently been made in the engineering of large telescopes. These include the development of large (up to 10 m in diameter) segmented mirrors based on new polishing techniques, ion milling for final figuring to a precise optical shape, and advanced computer-controlled alignment of the segments. Spin casting of large blanks has simplified the production of mirrors up to 8 m in size with near-final shape.
A particularly exciting development is the use of "adaptive" telescope mirrors to compensate for the distortion of stellar images produced by atmospheric turbulence. This technique makes use of a deformable mirror calibrated with the image of either a natural star or an artificial star produced by a laser. (An "artificial star" is formed by using a laser to create a tiny glowing spot high in the atmosphere.) Using adaptive optics, ground-based telescopes are now demonstrating diffraction-limited performance, albeit over relatively small fields of view. It can be expected that large ground-based telescopes will have higher resolution and light-gathering power than space-based telescopes, since both of these performance metrics depend on aperture size and ground-based telescopes can be larger than space-based ones. As an example of the performance gains associated with adaptive optics, Figure 3.6 shows an image without and with adaptive optics turned on at the 2.5-m Mount Wilson telescope. As can be seen, the increased resolution is dramatic. The adaptive optical system displays 0.07-arcsecond resolution, which is almost a hundred times better than past ground-based telescope systems but uses a telescope built approximately 80 years ago! The system on Mount Wilson uses a natural guide star. A related experiment at the 1.5-m Starfire Optical Range telescope at Kirtland Air Force Base, New Mexico, uses a yellow laser guide star
as a reference for its adaptive optical system. Since the field of view of a state-of-the-art adaptive optical system is relatively small, it is necessary to have a guide star near the object to be studied. The laser guide star concept permits the (artificial) guide star to be placed anywhere in the sky that the telescope is aimed. A closed-loop laser guide star adaptive optics system has recently been developed at the Lick Observatory, and one is now under development for the 10-m telescope at the W.M. Keck Observatory on Mauna Kea, Hawaii. It should be added that similar adaptive optics or "rubber mirror" techniques are also being used for compensation of distortions within laser cavities (commercial lasers and the National Ignition Facility laser fusion system) and in manufacturing processes to correct for aberrations.
Recently, the Keck Observatory incorporated two individual optical telescopes to be linked as interferometric arrays so that individual images can be coherently added, thus increasing the spatial resolution and sensitivity compared to a single telescope. Such techniques have been used for years in radio astronomy (employing radio frequencies) and during the past few years for specialized optical studies, but this is the first time the technique has been used in the optical portion of the electromagnetic spectrum for general telescopic observations.
Over the past few years, the development of ultrasensitive electronic detector arrays, first in the UV and visible and more recently in the IR, has helped to automate the data collection process. These electronic arrays produce image data in electronic form, which can be processed and accessed over the Internet. This provides rapid data access to a much larger group of scientists than earlier imaging modalities. It also facilitates the remote operation of telescopes. The development of sensitive large-area charge-coupled device (CCD) detectors and associated data reduction techniques has also had a major impact on astronomy. Such arrays have led to the recent observation of gravitational lensing due to "dark massive objects" (i.e., "machos"). Finally, either ground-based or space-station-based imaging sensors will be used to detect debris in low Earth orbit.
Planetary and Space Probes
Unique optical instruments have been used for several decades for planetary, astrophysics, and Earth remote sensing from orbital and interplanetary platforms, including the detection and measurement of the temperature and atmospheric composition of planets (Venus, Mars, Jupiter), comets (Halley), and other celestial bodies. Optical spectroscopic cameras or imagers have obtained close-up spectrometer images of planets, asteroids, and satellites for discerning atmospheric gases and surface composition and the dynamics and evolution of planetary surfaces and atmospheres. Low scattered light imaging spectrometers have
been used to yield information on mass exchange between binary stars, planetary system evolution, and stellar atmosphere surface science. The optical cameras and optical spectrometers on the Voyager and Galileo missions to the outer solar system, and those on-board the Viking and Pathfinder Mars lander-orbiter, provided images that have changed our fundamental view of the solar system and of mankind's role in the universe. Figure 3.7 shows an example of such an instrument used in the Galileo space mission.
The Hubble Space Telescope (HST) provides data for frequent new astronomical discoveries. A second-generation telescope, called Hubble II, is now on the drawing boards and will significantly exceed even HST's excellent performance.
A new NASA mission, the Origins Program, will search for life in the universe. One part of this program is to design and build a space optical instrument to detect and characterize planets around stars. Of recent importance was the Clementine mission, which detected water (H2O) on the moon using a polarimeter.
The Origins Program and many planned NASA science missions depend on the development of new lightweight, compact, advanced optical instruments. Toward this end, expected improvements in image detector array complexity and resolution, and more sophisticated spectroscopic instrumentation, will greatly enhance the opportunities in space science. Among recent technological advances that will enable new space science are ambient temperature IR detector materials for the spectral range from 2 to 5 μm, agile spectroscopic optical filters, lens optimization modeling, and integrated optics spectrometers. These particular developments are examples within an extensive optics program technology structure that can be categorized into several generic components: optical testing, wavefront sensing and control, and spectroscopic sensor optical systems. All of these instruments and new technologies must operate in the demanding environment of space: very wide temperature excursions; zero gravity, which may cause misalignment of Earth-built instruments; possible exposure to UV light, x rays, and ionizing particles; and the ability to operate unattended for several years with high reliability. These harsh environmental conditions drive requirements for special materials, devices, and designs.
Industrial Chemical Sensors
A wide range of optical sensors are used in industry, and their application is growing rapidly in certain selected cases (Janata et al., 1994; Warner et al., 1996). One example is the use of submersible fiber-optic probes to control the flow and level of liquid chemicals and distillation processes. Other important applications include absorption spectroscopy optical fiber sensors to monitor the concentration of liquid and gas products; optical fiber-routed Raman spectra instruments used in distillation columns for control of chemical reagents and products; and specific chemically coated fiber tips that react only with a particular set of ions, enzymes, antibodies, or sugars. Many of these sensors use glass, silica, or hollow fiber-optic pipes to route the optical beam to a remote location for analysis. As a result, one of the main advantages of optical chemical sensors is that the chemical or substance can be measured in real-time and in situ, with no need to extract a chemical sample and take it back to the laboratory for analysis. This is a significant advantage in monitoring a chemical reagent or substance in a hot reaction stack, in a flow chamber, or underground within a radioactive waste site.
The current annual U.S. market for optical chemical sensors is several hundred million dollars. It represents a niche market at present but is growing rapidly. Optical chemical sensors are still about 5 to 10 times more expensive than conventional chemical-related sensors, so current work is being conducted to make them cheaper, smaller, and more competitive. It is anticipated that future advances in semiconductor laser materials and manufacturing techniques will assist in this goal and produce a chemical sensor on a chip. It may be added that during the past year there have been several implementations of optical sensors on chemical production lines for real-time process control, and the results have shown considerable enhancement in the yield. It should be noted that traditional chemical analytical laboratory instruments often use optical or spectroscopic techniques to measure or detect the presence of trace compounds. The market for atomic spectroscopic instruments, for example, is shown in Figure 3.8. However, it is difficult to compare market sizes because data are not widely available.
The use of optical chemical sensors is growing in many major manufacturing sectors, including pulp and paper, semiconductors, petrochemicals, pharmaceuticals, steel, and glass. Many of these industries have their own professional or industrial societies that coordinate, promote, or fund sensor-related technology in their area. For example, the American Chemical Society (1996) has made several recommendations for the future competitiveness of the chemical industry, including the development of high-performance, real-time spectrometric instrumentation and the promotion of centers of excellence focused on chemical
measurements and process control. There is little coordination or dissemination of information between industrial sectors, however, and there is much duplication in the development of sensors by various institutes and industrial research laboratories. The Department of Energy (DOE) and the National Institute of Standards and Technology (NIST) have programs to assist in such cross-sector transfer, but they are small to moderate in size and often emphasize a particular segment of manufacturing, such as industries that require large amounts of energy (steel, aluminum) or ultraclean gases (semiconductors, pharmaceuticals). There is thus a current need to better coordinate and disseminate information and results. The private sector will probably accomplish this eventually through trade publications and industrial trade shows, but it could be accomplished faster if such coordination was fostered by a government or industrial program or institute.
Finally, new laser and optical sensors have been developed for metrology (remote measurement of position and flow). For example, laser sensors have recently been used to measure the depth and flow of molten aluminum in a large aluminum production plant in Norway. These sensors have a depth accuracy of 0.25 mm and have increased process yield considerably. In addition, a photoacoustic instrument utilizing a wavelength-tunable CO2 laser and acoustic sensor is operating in an air conditioning-refrigeration factory to monitor refrigerant leaks down to 0.1 ounce per year. Such metrological sensors are covered in more depth and breadth in Chapter 5.
Digital, Video, and Thermal Imaging Cameras
Video or television cameras have been in use for more than 50 years, but they have become household items only within the past 15 years as a result of the development of new, compact silicon semiconductor
video detector array chips (as opposed to older vacuum tube video detectors). Mass production of these video CCD array chips has brought their cost down to about $10 each. They are now used in video phones, camcorders, and surveillance systems, with an overall annual U.S. market for video cameras on the order of $1 billion. This market is fairly mature and stable at present, although advances are being made in the technology (e.g., image stabilization, electronic zoom, and lower light level detectors). The number of resolution elements (pixels) in these video cameras is usually about 500 x 500 at present.
A new, rapidly growing segment of imaging detectors is the development of digital cameras that use CCD detectors instead of photographic film. These cameras will be used as a replacement for traditional photographic film in digital cameras, photocopiers, and the printing industry. At present, several companies (Kodak, Casio, Chinon, Fuji) produce moderate-resolution 300,000-pixel digital cameras that allow for digital storage of pictures and their transfer to a computer or floppy disk. They cost only about $300 to $1,000 each at present, with cost reductions expected in the future. Manufacturing rates approach 10,000 per month at some larger camera companies. A new line of high-resolution CCD digital cameras is now being produced by Kodak that uses a 6,000,000-pixel CCD chip to detect the video image. These are equal in resolution to ISO 400 photographic print film and produce a picture equal that of the best single lens reflex (SLR) cameras. Such digital cameras cost on the order of $15,000 but provide software that allows for off-line image manipulation. These digital cameras are expected to be used in conjunction with laser color copiers in the printing industry, with projected camera sales on the order of $1 billion per year. This marriage of high-resolution optical CCD cameras with widespread home computer image manipulation is expected to completely change the photographic and printing industry from analog photographs toward digital computer images.
There is a large (several $100 million per year) worldwide commercial and industrial market in thermal imaging cameras and radiometer (temperature) instruments. These can be used in a wide range of applications, including the imaging of hot machinery due to friction or misalignment (see Figure 3.9), the location of overloaded circuit breakers in an electrical distribution network that may be on the verge of failure, and monitoring the uniformity of cooling of the output from a paper pulp mill. The thermal imaging cameras used in these applications can be cooled or uncooled, with cooled detectors used to image smaller temperature differences (AT). Many of the cameras use PbZr detector focal plane arrays and cost from about $20,000 to $50,000 for handheld systems used in industry to $50,000 to $200,000 for airborne systems used to detect humans on the ground or their warm temperature
trails. Many of the most sensitive cameras are cooled using a closed-cycle Sterling cooler so that no external cryogenics (liquid nitrogen) is required. Significant improvements in these commercial thermal imagers have been made recently, including smaller ΔT values (on the order of 0.1°C) that can be detected, higher spatial resolution that can be displayed so that a separate video camera does not have to be used, and lower production costs. The market for thermal imaging cameras is growing rapidly because of these factors and an increasing number of applications in industry.
Significant progress has been made recently in the development of infrared focal plane array detectors for low-intensity and small-ΔT applications, led by significant DOD investment in HgCdTe arrays for very low-intensity applications and in high-resolution PtSi and Si:As infrared arrays approaching 1000 x 1000 pixels. These have been developed with DOD and NASA funding for military night vision cameras and IR signature studies. The Si:As detectors are sensitive to long-wavelength (30 μm) IR, but they have to be cooled to 10 K. The Pt:Si detectors operate at cryogenic temperatures, are sensitive to 3- to 5-μm radiation, and can be used in surveillance to detect the warm temperature of a person hiding in foliage or to image relatively warm aircraft against the colder background of the sky. The cost of these last two detectors is still high, between $20,000 and $100,000 each, but this is expected to fall as increased production occurs. Also of importance is the recent development of uncooled silicon microstructure bolometric array detectors that have wide use as thermal and IR imagers. Their performance approaches that of staring cryogenic IR imagers, and they cost far less.
Law Enforcement and Security
Optical sensors play an important role in law enforcement and security. They are used in night vision scopes for border patrol and surveillance, in motion sensors for home security alarms, and to detect physical specimens at crime scenes. Examination of physical evidence is usually done with the ubiquitous microscopes and standard laboratory analytical chemical techniques. As in the case of industrial chemical sensors, a significant amount of new research is being conducted in the potential use of optical sensors in law enforcement, with a large fraction of new applications using newly developed sensor technology from DOD. However, analysis kits are needed that are portable and can be used easily at a crime scene.
Most common home and business security surveillance systems involve the use of video cameras placed at remote locations. Recently, new cameras have become more readily available that operate at very low light levels (starlight) or in the infrared for nighttime surveillance. For instance, Figure 3.10 shows a camera or scope used by recreational fishermen to navigate at night; these are also being used for border surveillance. Current optical monitoring of the U.S. border by the Border Patrol relies primarily on the use of thermal FLIR (forward-looking infrared) imaging systems and night vision goggles. As the new room-temperature IR video cameras (described earlier) become more readily available and affordable, they will enhance border patrol and civilian police surveillance efforts. Additionally, the next generation of CCD and innovative microchannel plate technologies will also place greater capabilities for visual surveillance in night operations in the hands of law enforcement officials. Further, as multispectral imaging cameras (hyperspectral) being developed for military applications become more affordable they will similarly enhance law enforcement surveillance capabilities. They can be used on low-cost, small, remotely controlled or autonomous airplanes to provide three-dimensional data at a moderate distance (2 to 5 km) in heavy rain, under most fog conditions, and under camouflage and smoke obscurants. This may be especially useful in providing an "eagle-eye" view of urban sites.
Several DOD agencies have recently started laser and optics application groups directed toward the application of new optical sensor technology for law enforcement and security. The programs include, for instance, the use of an invisible infrared searchlight and camera
to locate people at night and the use of the "cats-eye" returns from people's retinas to locate potential snipers. Other potential applications being studied include high-power (1-W) visible lasers that can illuminate a criminal at night to indicate his impending apprehension and helicopter-borne 10-W IR laser "spotlights" coupled to a night vision scope and telescope, which have been shown to double search capability.
The common household motion sensor used in home security alarms employs infrared detectors that sense the movement of a warm body against the colder background of the room. These motion sensors are relatively cheap ($30) and have sales of several million units per year. They have no spatial resolution (i.e., they cannot locate the detected body) but serve well as a general warning of a security breach. They would have to be augmented with the new room-temperature IR camera to determine the actual position of the intruder within a room. Such a system could be augmented with a time-domain radar using micropulses to determine the exact location and distance of the intruder.
Drug and Explosives Detection
It has long been thought that optical and laser sensors could be used to detect the presence of drugs or explosives, since in the laboratory, laser-induced fluorescence and frequency-modulated spectroscopic detection techniques have been used for the detection of very small amounts of gases and molecular substances. However, in practice, the sensitivity of these techniques for the detection of minute or trace amounts of drugs or explosives has been shown to be much reduced in the presence of other chemical or background compounds often found in everyday situations. As such, the optical detection of drugs and explosives in their final bulk form has not proven a useful means of detection compared with analytical chemical detection techniques such as x-ray computed tomography, thermal neutron activation, mass spectrometry, neutron thermalization, ion-trap time-of-flight mass spectrometry, gas chromatography/mass spectrometry—or even trained dogs (SPIE, 1996a,b). However, it may be possible to use specific sprayed reagents that form colored compounds when they come in contact with explosive and/or drug vapors to detect the presence and concentration of each; another technique being analyzed is to place a tracer element in explosive agents that can be more easily detected and identified. Also, there is the potential use of IR radiometry techniques that would detect explosives by the difference in their heat capacity relative to their surroundings (e.g., in the case of explosive mines). This technique requires long-term observations and either thermal or microwave illumination before observation and is not yet deemed viable for general use.
Often it is important to locate a drug manufacturing site. In theory, this can be done by various techniques using the optical and laser remote sensing technology described earlier in the discussion of environmental and atmospheric monitoring. One can detect a drug factory's effluent of chemical solvents and reactants and then identify it either by differential absorption light detection and ranging or by hyperspectral infrared imaging. Further, the physical location of a facility hidden by foliage or camouflage can be detected by a compact airborne multispectral imager or by a laser detection and ranging (lidar) seeker. The sensitivity of such a device has not yet been demonstrated at the detection levels required for practical remote surveillance, although progress is being made.
Forensics and Evidence Examination
The use of optical techniques in forensics and law enforcement for the examination of physical evidence is growing but is still not an accepted practice in general, except for optical microscopy, photography or video, and more recently, DNA analysis. In general, optical sensors are not used in forensics, because they cost too much, they are not portable enough to be taken easily to a crime scene, or other more established techniques are already being used. Most physical evidence is currently examined by standard chemical analysis, with little use of optical instrumentation except optical microscopes. Confocal optical scanning microscopes with high spatial resolution are now being used in Canada but not the United States. Two exceptions are the enhancement of fingerprints by laser fluorescence and the detection of some bodily fluids (blood, semen) using filtered lamps to excite fluorescence of the specimens (Menzel, 1989). The latter technique is employed at crime scenes where portability is important, in contrast to the laser-enhanced fingerprint system, which is laboratory based because of the large laser size. This situation is expected to change as new, efficient, compact diode-pumped UV lasers and time-resolved imaging systems are developed.
The analysis of DNA evidence uses laser tagging of the DNA sequencing segments; it is just starting to be employed by law enforcement agencies. However, as always, care must be taken to ensure that the evidence is not contaminated with additional DNA specimens. This requirement shows the need to develop self-contained portable laboratories for the analysis of evidence.
It is felt that low budgets and lack of training are hindering growth in this area in the United States. Research support for new optical sensing techniques for forensics is only about $1 million to $10 million per year in the United States but is higher in Europe.
Finally, optical systems will play a greater role in the detection of counterfeit money since most anticounterfeit sensors will use optical or holographic techniques to detect hidden patterns and embedded markers in the bills. This will be a growth area as U.S. bill designs become more resistant to counterfeiting and detection devices become cheaper and more prevalent. It should be noted that an NRC report addressed counterfeit detection techniques (National Research Council, 1993).
Common Everyday Optical Sensors
A variety of optical sensors and instruments are used every day and manufactured in large quantities; in some cases, these represent significant financial markets. Although some of these devices are discussed in Chapter 6, they are listed here because they rely on optical sensors as the basis of their function. Examples include optical bar-code readers, garage and elevator door safety sensors, television remote controls, ''ear" infrared thermometers, night-activated photoelectric light switches, infrared coupling of personal computers to keyboards and printers, and infrared switches that automatically turn on and off the water faucets in public restrooms. Bar-code readers use either an invisible infrared optical beam or a red, low-power helium-neon laser (supermarket scanner) to scan and detect the reflected light from the pattern of the bar-code. Bar-code scanners are now used on most manufactured goods for inventory control, including rental cars, railroad cars, packaged food, parcel delivery, and most items sold at retail; Figure 3.11 shows one common type. Garage door and elevator door safety stops often use an invisible infrared beam directed across the bottom of the door, so that someone in its path can be detected and closing of the door stopped; a similar photoelectric eye is used to record and time track, ski, and race events. Television remote control devices ("clickers") work by emitting a very low power, pulse-coded infrared (LED) beam that is detected and interpreted by the television set as an instruction to change channels and so forth. Infrared thermometers have recently become available for less than $30 that measure IR thermal emission from the eardrum and deduce the blackbody temperature of the patient. These devices have proven accurate and are very important for use on children. Photoelectric switches have been used for more than 50 years to turn city streetlights on and off according to how dark it is; they have also
been used in homes to conserve battery life in accent lights powered by solar cells. Automated infrared proximity sensors are used in many public restrooms to turn on faucets and lavatories.
The market for these sensors is estimated at several hundred million dollars per year, and for bar-code scanners about $1 billion per year.
A variety of optical sensors are used in common devices related to communication and information processing. Fax machines use a long linear array of optical sensors to measure and image the scanned input paper for subsequent transmittal over phone lines. Optical copiers use either a traditional light source (a xenon lamp) for black and white prints or a laser scanner to image and form a color print. The laser computer printer has been widely available for the past 10 years and uses a semiconductor diode laser to write extremely small dots onto a toner cartridge and paper.
DOE, NIST, and industry, in cooperation with the technical and professional societies, should pursue a program to enhance the coordination and transfer of optical sensor technology among industry, academia, and government agencies.
One of the most important uses of optics by society is in the form of lighting. Lighting systems represent a major economic market, with annual U.S. sales of lamps and fixtures worth about $10 billion and related electricity costs of about $40 billion each year; the latter figure represents about 19% of total U.S. electricity consumption. Because these numbers are so large, a small increase in lighting efficiency represents a large savings of energy and cost. There have been steady efficiency improvements as a result of better fluorescent lamps, better reflective and radiative coatings in incandescent bulbs, and new concepts such as light-emitting diodes. This section presents some of the new and exciting advances that are being made in lighting sources and distribution technologies. It should be noted that several U.S. government agencies, university research institutes, and industrial associations have major programs in energy and lighting efficiency improvements. For example, the Department of Energy has a consortium of several major research programs, funded at about $210 million in 1996, with about $110 million for weatherization assistance and $9 million for research in lighting. The Environmental Protection Agency has the highly successful applied Green Lights program to assist companies in reducing their energy costs, including lighting, with some companies reporting savings near 50%.
Lighting History, Future Directions, and Standards
Artificial lighting is a rather recent technological advance in terms of human history, having become a useful technology only within the past 50 to 100 years. Historically, artificial lights existed for thousands of years in the form of fire (torches), but this changed radically with the invention of the incandescent lamp in the 1840s by DeMoleyns and Starr, followed by the first successful commercial (mass-produced) lamp in 1880 by Edison. Similarly, low-voltage fluorescent lamps were invented by Meyer in 1926, followed by their commercial production in 1938 by the General Electric Company. Since that time, several other light sources have been invented and used, such as the mercury vapor, metal halide, high-pressure sodium, and halogen lamps, and most recently the sulfur-dimer (microwave discharge) and LED light sources.
One measure of the utility of these different light sources is the output light generated (lumens) per input electrical energy (watts), including any ballast electronic losses. A lumen is a radiometric (physical optics) power unit related to the total light intensity (UV, visible, and IR or heat) given off by a blackbody radiator of white-hot platinum at 2,000 K (3,100°F) and human-eye spectral sensitivity data collected under bright lighting in the 1920s. Figure 3.12 shows the efficiency of various light sources and indicates the theoretical maximum value of 220 lumens per watt. Although the figure is interesting and shows the improvements expected in several new light sources, it is only a part of the story and does not indicate several very important, photometrically related visual parameters such as (1) color index efficiency (ability to view different colors); (2) changes in human visual color response at
low nighttime light levels; (3) ease of distribution and ability to focus light; (4) role of the photic system (human response-biological clock); and (5) degradation of the light source. All of these factors influence the efficacy (effectiveness) of the light source, including its efficiency, the directional nature of the ability to focus light (lumens per steradian of solid angle), the efficiency of distributing light to a distant place, and the human visual response (color and contrast) at different light levels. For instance, although sodium lights have a high-efficiency in terms of lumens per watt, they are poorer for viewing colors at night than metal halide sources. Also, although incandescent or halogen lamps have a lower lumen efficiency than fluorescent lamps, they are more effective in delivering light to a specific location (e.g., as in an automobile headlamp) because they can be focused better into a beam. On the other hand, the sulfur-dimer lamp has very high-efficiency, but it is more difficult to deliver the light efficiently to distant locations where it can be used by people to see.
For these reasons, it is important that light sources be judged not only on their energy efficiency but also in terms of human visual response and ease of distribution. A set of standards encompassing all of these effects is being worked on by universities, industry, and government agencies, but it has yet to be universally adopted. Such standards would be extremely helpful in light source selection and would help to direct future research in this important area. It is therefore extremely important that there be coordinated activity in this area from the major research institutes and associations, including university research institutes, DOE, EPA, the Electric Power Research Institute (EPRI), and the National Electrical Manufacturers Association (NEMA).
New Lighting Sources and Distribution Systems
New lighting sources and distribution systems are being actively studied, with considerable work being done on making existing light sources more efficient, developing new kinds of light sources, and developing new distribution or high-efficiency transmission systems. This section discusses some recent exciting developments.
Conventional Lighting (Incandescent, Fluorescent, and High-Intensity Discharge) and Fixtures
The majority of light sources used today are incandescent, fluorescent, or high-intensity discharge (HID) lamps. (HID lamps include high-pressure "white" sodium, metal halide, and mercury vapor.) Although many of these kinds of light sources have been around for more than 50 years, lamp manufacturers continue to make improvements in terms of efficiency, lower cost, and better maintenance. Half of the lamp products on the market today did not exist 4 years ago.
These new lamps include parabolic aluminized reflector (PAR) incandescent lamps, IR coated lamps with a ceramic cylinder to reflect heat back to the tungsten filament, and metal halide lamps for residential table lamps and automobile headlights. Metal halide lamps are the fastest-growing category, since they produce a white light at night; they are also rapidly becoming the main choice for ceiling lighting in large discount stores. Fluorescent lamps were the focus of development just 5 or 10 years ago, but metal halide lights are expected to see the most activity and advancement in the next 5 years. Considerable evolutionary progress has been made in this area and will continue to be made.
Such progress has not been seen, however, in the related area of lighting fixtures (luminaries), on which the lighting industry spends little for research. Most innovations in light fixtures took place in the first half of this century; relatively little has been done since. Because lighting is a system, it is important to have not only an efficient light source but also an efficient way to distribute or place the light where it is needed. Light produced by the most efficient lamp in the world is wasted if the lamp is placed in a black box. There should be more research and development on lighting systems overall, in the context of how a person will use the system to see.
Sulfur-Dimer (Microwave Discharge) Lamps
One of the more promising new light sources at present is the sulfur-dimer (S2) lamp that mimics the color spectrum of sunlight and uses an electrodeless inductively coupled (microwave) discharge with an overall efficiency of 50%. A 100-W sulfur-dimer lamp has the same light output as a 1,500-W incandescent lamp and currently costs about $500, although prices are expected to come down as the technology becomes more widely used. The S2 lamp may offer significant enhancements in building lighting, using a single high-intensity lamp and light pipes to distribute the light to other rooms. Lifetime tests are now being conducted with these lamps, and the results are quite encouraging. Distribution of their light is difficult, however, since they require that light pipes be built into new buildings. Such high-efficiency distributed lighting may profoundly change the architectural design of future commercial buildings, since lighting and the associated electricity costs have a major impact on the overall cost of such buildings. Their utility for residential buildings remains to be determined.
Routing of Light by Fiber-Optic Cables or Hollow Pipes
Another new form of lighting uses plastic fiber cable bundles to transmit or route light from an efficient metal halide lamp to distant points. These systems do not transmit heat or UV and can be changed in color. However, a drawback of fiber-routed sources as a main light source is that the efficiency of transmission of visible light and the ability
to focus it effectively at the distant end are not very high. Such lighting is therefore rarely used for general illumination but is rather employed for accent lighting, remote walkways, and architectural accents. For example, the 42-foot-high Coca Cola sign in New York's Times Square uses 30 miles of fiber-optic cables to distribute the light used to form the sign's image. Such signs are rapidly starting to gain a share of the worldwide $40 billion annual market for neon signs, since the plastic-routed light uses 50% of the electricity of a standard neon sign. At present the worldwide market for these types of lights is about $60 million per year, but it has been growing by a factor of two each year for the past 3 years and is expected to reach several billion dollars per year in the next decade.
Controlled Light-Reflecting Windows
Another area related to lighting is controlled-reflectivity windows for homes and businesses. Low-transmission or low-thermal-loss glass windows have been sold for years, but a related technology involves electrically controlled windows in which the visible or IR reflectivity of the glass can be changed by a controlling voltage. Materials and systems for such electronically controlled light-reflecting windows (electrochromics) are being studied worldwide by several groups. Electrochromics are being used in small-scale applications, such as rearview mirrors for cars and trucks. Coupled with a light-level sensor, they can be used for rapid control of the mirror's reflectivity at night. For use in large windows, however, large-scale, cost-effective, durable coatings have not yet been reliably produced. Their successful development could have far-reaching consequences in terms of reducing overall energy needs (lighting and heating or cooling) for residential and business use.
Light-emitting diodes are a relatively new (past few decades) light source produced by semiconductor manufacturing techniques; they are used for displays in a wide range of consumer electronics. Until now, they have been used mainly as indicator lights in clock radios and TV remote controls, not being bright enough for use in lighting. Two recent breakthroughs, however, have significantly enhanced the prospects for LED use in a much wider range of applications: Blue and green were added to the spectrum of efficient LEDs through the discovery of improved semiconducting properties in gallium nitride, and better designs have led to much improved efficiency. At certain wavelengths, better than 20% efficiency is commercially available. Internal efficiencies are close to 100%, so the only question is how much of the light can be extracted before it is parasitically absorbed in the device structure. It can be projected that design improvements will
allow commercial LED efficiencies to exceed 50% in due course. Because of these high efficiencies, LEDs can potentially be used as lighting sources. In addition, since LEDs have a lifetime of 30 years in intermittent operation, their use eliminates the sometimes expensive labor cost of changing light bulbs or handling the waste (burned-out light bulbs). These factors are extremely important in many applications.
These recent developments would seem to portend considerable growth into new markets. Displays, architectural lighting, and many other traditional markets for LEDs are expected to expand. In addition to LED market growth, there are benefits in energy conservation. For example, room-temperature blue and green LEDs have been commercially produced with high-efficiency so they can be used with existing red LEDs to produce "white" light. Another white-light LED lighting concept uses a blue LED coated with a broad-wavelength emission phosphor; these glow with a white light at an intensity strong enough that looking at them is painful. These white-light LEDs are now equal in efficiency to incandescent lamps and should compete in efficiency with fluorescent lamps in 5 years. However, at present, their cost is prohibitive—about $300 for a white-light searchlight—but it is expected to come down as manufacturing costs are reduced. For example, several large companies (such as Hewlett Packard and Phillips) have formed a joint venture for the commercial development of white-light LEDs as competitors to light bulbs.
As an example of the large market potential, several U.S. companies have started to sell replacement LED red traffic lights for as little as $200 each (see Figure 3.13). Current sales are about 60,000 units per year, with a much larger potential market estimated, given that there are about 250,000 traffic intersections in the United States with an average of 10 red traffic lights at each. The electrical cost of a red light bulb traffic light is about $6 per month, versus $0.85 for the LED alternative. At present, the total annual electrical cost for conventional red traffic lights is about $200 million, which would be reduced to about $25 million by using LEDs, for a savings of $175 million each year in the United States alone. The city of Philadelphia has started to replace all red traffic lights over the past 4 years and expects to save several million dollars per year in electrical costs as well as significantly reduced replacement costs. In addition, China and many other developing countries are starting to use LEDs in traffic lights and related signs because their use will reduce the need to build new electrical generating plants in the future.
There is now ample reason to believe that manufacturing improvements will allow the cost of producing LEDs to come down, much as it has for other semiconductor products. New types of reactors are now available, as mentioned later in the discussion of solar cells, that will make metallo-organic chemical vapor deposition (MOCVD) epitaxial growth a much cheaper process. Moore's law, the exponential decline in semiconductor product costs, can be expected to apply to high-efficiency LEDs as well. In addition, similar advances are expected in the GaN family of semiconductors and in the development of longer-lived organic LEDs. Thus, although the current LED market worldwide is about $2 billion per year, it can be expected to grow considerably, perhaps by an order of magnitude within the next decade.
Lasers and Lighting in Live Entertainment
The entertainment field uses optics in a variety of ways, from movie projectors, to television and video game displays, to optical illusions and laser light shows. This section emphasizes the use of optics and lasers in live performance entertainment and laser light shows, since most of the other areas are covered elsewhere in the report (e.g., the discussion of displays in Chapter 1).
Live entertainment such as rock concerts and theme park stage shows uses a considerable amount of lighting and laser light shows. The use of specialized lighting and laser light shows represents an enhancement of the primary entertainment of these performances. The laser or light show itself is usually considered secondary to the main performance, however, although in some cases, such as in Las Vegas and at Disney World, the laser light show is a major nightly production. The overall market for the use of lasers in this field is about $20 million to $50 million per year, with an expenditure of $500,000 to $2 million per tour not uncommon for a major rock band. The use of optics and lasers in live entertainment is stable, with significant growth not expected at present. It should be added that eye safety is always a concern for laser light shows and is often handled by making sure that the laser beams are directed above and away from people in the audience. In an outdoor laser show where the beam is shot upward into the sky, some production companies are now using a radar system to detect aircraft flying close to the laser beam so that the laser can be blocked as appropriate.
DOE, EPA, EPRI, and NEMA should coordinate their efforts and create a single program to enhance the efficiency and efficacy of new lighting sources and delivery systems, with the goal of reducing U.S. consumption of electricity for lighting by a factor of two over the next decade, thus saving about $10 billion to $20 billion per year in energy costs.
Optical Sensors and Lighting in Transportation
Optical sensors, lighting, and optical instruments are used to a large extent in automobiles and to a smaller degree in aircraft. This section covers the use of optics and the potential advances in their use in the area of transportation (aircraft and automobiles) because these represent some of the largest industrial sectors in our economy.
Considerable research has been conducted on the use of optics in aircraft, ranging from the fly-by-light concept, in which aircraft surfaces are controlled by fiber-optic control systems, to optical sensors for precise measurements of airspeed and the pressure in front of the aircraft. In general, however, conventional mechanical and electrical techniques still have cost and reliability advantages, especially because of the wide range of operating temperatures in aircraft (-50 to +120°C). Some uses are advantageous for optics, including the use of optical fiber to distribute audio and video entertainment in passenger aircraft and the use of laser gyroscopes for stand-alone navigation. Laser gyroscopes use a small laser beam inside a stable ring cavity to measure the acceleration and position of the aircraft with an accuracy of several feet, thus permitting the aircraft to navigate over continental distances. The current market for laser gyroscope systems is about $400 million per year, of which $100 million is the cost of the ring lasers. Figure 3.14 shows a picture of a ring laser gyroscope (RLG) like those used in many commercial aircraft today. It is anticipated that satellite-based Global Positioning System (GPS) instruments may eventually supplant laser gyroscopes, but not for the next few years.
Other potential uses for optical instruments include Doppler laser radar to detect wind shear in front of landing aircraft or wake vortices at airports. At present, most commercial aircraft are planning to use Doppler microwave radar for wind shear detection, based on recent flight tests by NASA and the Federal Aviation Administration (FAA), but these agencies are also testing new solid-state Doppler laser radars for airport wake vortex detection, which offer advantages in dry air turbulence conditions.
Finally, for high-speed or stealth aircraft where mechanical pitot tube air speed sensors are inaccurate or create an undesirable radar return, optical sensors using Doppler laser radar are being developed to measure air speed and air density at distances 5 to 10 feet in front of the aircraft, outside the aircraft's shock front. Such a sensor is also being studied by NASA for use in the high-altitude Super Sonic Transport, which will use ramjets for propulsion. Ramjets require very precise information on the density and velocity of the incoming air to avoid flameouts and optimize combustion at high altitudes.
Optics has been used in automobiles for the past hundred years, ever since someone needed to drive at night, and even before that in horse-drawn carriages. Today optics is used extensively in automobiles, and its use is growing as cheaper, more compact light sources and optical devices become available. Traditional lighting applications still dominate, such as headlamps, taillamps, and instrument displays. A number of new, non-lighting applications are also being found, however, such as optical fiber strain gauges embedded in roadways and bridges (Box 3.2) and optical sensors for the control functions required for precise computer control of modern engines (e.g., sparkplug timing and sensing of engine rotation and position). The cost of these optical items is important, because traditionally the individual unit component cost in automobiles is on the order of a few dollars to a few tens of dollars. The total cost of optics in each vehicle sold today is estimated to be about $100 to $200. Annual U.S. production is about 15 million vehicles, so the total U.S. market for vehicular optics is on the order of $1.5 billion to $3 billion per year.
New applications of optical materials and systems for sensors and lighting are being pursued vigorously by the auto companies. For example, high-intensity (blue-white) arc discharge lights will be used as headlamps on many vehicles since they last longer and are more efficient than the conventional incandescent sources they will replace. The efficiency gain is particularly important for electric vehicles. HIDs are already available in some luxury car lines. LEDs are starting to replace conventional lamps in rear and brake lights because of their longer lifetime, smaller package size, and greater optical efficiency (15% for red light compared with 1% for a filtered incandescent bulb). Simple reflective heads-up displays, which display information on the windshield, are already available in some vehicles and more sophisticated versions are being planned. The next generation of instrument-panel displays is expected to use full-color, fully reconfigurable, flat-panel devices with sufficient brightness for daytime use in the passenger compartment. Vacuum fluorescent technology is the leading contender for this application, but there are many competitors.
BOX 3.2 OPTICAL FIBER STRAIN GAUGES IN HIGHWAYS
An emerging application of optical sensors in transportation is the use of embedded optical fiber strain gauges in bridges and roadways. Optical strain gauges are more durable than conventional foil and piezoelectric gauges and are immune to the electromagnetic interference that plagues electronic gauges. Because optical fibers are small, they can be embedded in concrete or asphalt without disrupting the structural properties of the surrounding material.
The Federal Highway Administration and other federal and state agencies are exploring various uses of these sensors. Bridge beams can be monitored for stresses during their fabrication and transport to the construction site. Bridge design ratings can be tested. Arrays of sensors placed below a pavement surface can improve the prediction of design lifetimes by collecting data on the loads imposed by passing vehicles. Sensors that monitor the deterioration over time of structures and pavements can help to prioritize maintenance tasks and increase safety by giving early warning of impending structural failure. Sensors embedded in highways can count and weigh passing vehicles while they are in motion to help in traffic planning and to enforce laws that restrict truck weights.
A system based on Bragg gratings has been developed that permits as many as 64 strain gauges to be put on a single optical fiber. This multiplicity greatly simplifies installation and reduces cabling requirements and the cost per sensor, and because the Bragg grating system senses wavelength shifts, it is more reliable and repeatable than approaches based on amplitude or shifts in interference fringes. Bragg grating sensors were first used in the laboratory to study the performance of beams and bridge decks. This research culminated in the installation of 48 sensors in a full-scale section of a reinforced-concrete bridge deck. The sensors monitored loads during the casting of the concrete, strains due to the subsequent curing and shrinkage, and strains under static and dynamic loading. Bragg grating sensors are now being applied in real field situations. An array of 32 sensors has been installed to monitor an interstate highway bridge in New Mexico that has developed significant fatigue cracks, and there are plans to install 128 sensors on the heavily traveled Woodrow Wilson Bridge outside Washington, D.C.
Bragg grating strain sensors illustrate the value of materials science in optical engineering. Because germanium-doped glass is sensitive to certain wavelengths of light, it is possible to produce the Bragg gratings in the fiber by photoengraving. Furthermore, because the Bragg gratings can be manufactured in a continuous-draw tower process, sensors can in principle be put on an arbitrarily long fiber. As a result, the unit cost of Bragg grating sensors is competitive with that of conventional strain gauges.
It is now realistic to consider installations of 1,000 or more optical fiber sensors. That possibility will create opportunities for advanced mathematical analysis of structural response and challenges for data management and visualization. It may lead to a radical rethinking of how and where strain gauges are placed in civil engineering structures.
Optoelectronic sensors using laser, LED, or microwave radar have the potential to be a major growth area for use in collision avoidance, laser ranging, and blind-spot warning of nearby vehicles or obstacles. New optics-based chemical sensors are being used to monitor catalyst efficiency by measuring the concentrations of such exhaust gas species as unburned hydrocarbons, carbon monoxide, and oxides of nitrogen using miniature spectrometric real-time sensors. An important concern for these optoelectronic systems is that they must operate over a wide temperature range, from -40 to +85°C; they must be vibration tolerant; and they must last the life of the vehicle (typically 10 years or 10,000 hours of operation).
Advances in the efficient generation of electricity can have a significant impact on the energy consumption of our society. It should be noted that the energy (including electricity, gas, oil, and coal) used in the United States each year amounts to about $600 billion, of which $200 billion is used in business and residential buildings.
This section covers several optics technologies that may have significant impact in this area, including the use of lasers to produce inertial confinement fusion as a future source of energy and for new basic science; the use of lasers to enrich uranium for reactor power plants; and recent developments in solar cell technology.
Inertial Confinement Fusion Using Lasers
Laser-induced inertial confinement fusion (ICF) is an approach to producing controlled nuclear fusion on earth (Lindl et al., 1992). As an integral part of the pursuit of a zero-yield nuclear test ban treaty, the United States has committed to the design, development, and construction of the glass-laser-based National Ignition Facility (NIF). The NIF is intended to use inertial confinement fusion for weapons studies, but it will also provide insight for future energy applications.
Figure 3.15 shows a drawing of the NIF facility, which is based on flashlamp-pumped neodymium-doped glass technology and frequency conversion. It is scheduled to be completed in 2002 and to produce 1.8 MJ at 350 nm, with a total project cost of approximately $1.1 billion. From 1995 to 1998, the United States will also invest about $170 million in this project for the development of laser technology, large-scale precision optical components, and low-cost advanced optics manufacturing methods. NIF will be the largest optical system in the world and will develop and employ state-of-the-art adaptive optics systems on each of its 192 laser beam lines. To further control the beams'
temporal and spatial coherence, NIF will use diffractive optics and phase modulation technology to produce optical bandwidths up to 0.5 THz.
Recent scientific and technological advances in efficient, powerful semiconductor laser diode arrays (as laser pump sources), in specialized crystalline laser gain crystals, and in sophisticated gas flow cooling techniques now permit the conceptualization of an efficient, multimegawatt, all solid-state laser suitable for driving a central electric power plant based on inertial fusion energy (IFE). The development and demonstration of a highly modularized 1-kJ unit beam line for such a laser system over 5 to 10 years represents a grand challenge that would drive the envelope of diode-pumped solid-state laser technology and lay the foundation for the timely pursuit of IFE after laboratory ignition is achieved at NIF early in the next century. A major advance required for IFE is to reduce the cost of laser diode arrays to less than 10 cents per watt.
Overall, ICF now amounts to about a $400 million per year project worldwide ($240 million in the United States in 1996). All funding for ICF currently comes from governments.
Although ICF has not yet been demonstrated, NIF is the next critical step. The spin-off value in its optics and laser advances is great, and the potential payoff as a new energy source is enormous, although still uncertain and many years in the future. The consequences are also wide-ranging for astrophysics and other sciences.
Laser Isotope Separation of Uranium for Nuclear Energy
Atomic vapor laser isotope separation (AVLIS) is an economical, environmentally improved method to enrich natural uranium for light-water reactor fuel. AVLIS is based on technology demonstrated over the past 20 years and uses a precisely tuned laser to selectively excite and photoionize uranium-235 (235U). The selectively ionized 235U is then collected to generate a product enriched in this isotope. It should be noted that the United States controls about 40% of the world's uranium enrichment market (currently several billion dollars annually) using technology developed 50 years ago. AVLIS will be able to produce enriched uranium at a much lower cost and will enable the United States to capture a significantly larger fraction of the world market.
The U.S. Enrichment Corporation, a government corporation formed in 1992 with plans to privatize, is refining the technology and designing a large AVLIS system for this purpose. Key plant systems consist of separators to vaporize the uranium and collect the selectively photoionized 235U. There will be several identical separator lines. Dye lasers generating 50 kW of process light are optically energized by 160-kW copper vapor lasers (or possibly solid-state lasers) distributed via a fiber-optic network.
The overall goal is to construct an AVLIS enrichment facility and bring it to full production early in the next century. The AVLIS project may become the largest technology transfer effort from DOE to the commercial sector.
Space Solar Cells
Solar cells, which convert light to electricity, have been used as the primary power in communication, defense, and weather satellites for the past 35 years and can be considered part of the satellite and spacecraft manufacturing industry. The worldwide space solar cell business is approximately $150 million per year, with about two-thirds of the total dominated by two American companies. The United States thus has a strong international position in this field, with a total annual market of about $100 million.
In the past 5 years, however, there has been a technological and materials revolution in this field. For 30 years before 1994, the technology was stable, using standard crystalline silicon solar cell technology. Then in 1994, gallium arsenide (GaAs) cells grown on germanium substrates became mature for space use and the market switched largely to GaAs cells. The inherent leverage in reduced area and weight associated with the higher-efficiency GaAs cells influenced the launch booster design and the overall system. Therefore, the added cost of the new technology was more than warranted, to the degree that it is now difficult to sell any but GaAs-based solar cells for space use. In fact, by
early 1996 the space market had moved to begin production of dual-junction and triple-junction InGaP-GaAs cells.
Because of the great demand for new space-based communications technologies, this market is booming. Telephone systems requiring 800-satellite constellations have been proposed, and several communications systems using up to 66 satellites have already been started. A major concern for the industry is the capital investment required to meet a demand surge that may not last long enough to amortize the equipment.
This industry is playing a leadership role in optoelectronics and optical materials, being the first to apply many technologies that will become more widespread later. For example, there is an opportunity to apply new high-speed MOCVD equipment, which is likely to allow low-cost, high-speed epitaxial growth. This equipment will eventually become standard in many other areas of the semiconductor manufacturing industry, eventually making high-quality epitaxial films much cheaper and creating new opportunities for their use in many fields.
Terrestrial Solar Cells
The terrestrial uses of solar cells can be classified into two general categories: on the power grid and off the power grid. Off-grid applications include supplying power for hand calculators, remote instruments, stand-alone communication gear, remote mechanical pumps, and refrigerators. Other important off-grid uses are for industrial and residential general-purpose power, particularly in remote locations. On-grid solar cell systems make up only a tiny fraction of the available electric power capacity of the United States. The fraction is expected to become much larger as the cost of solar cells declines, the conversion efficiency of sunlight to electrical energy increases, nonrenewable fuel becomes scarcer and more expensive, and greenhouse gases begin to severely impact the environment. To quote the senior managing director of the Royal Dutch/Shell Group concerning renewable energy usage in general (Herkströter, 1997):
. . . our various scenarios suggest that renewables could provide some 5% of the world's energy by 2020. They also suggest this could rise to over 50% by mid-century—a shift as fundamental as that from coal to oil in this century.
The United States currently spends approximately $600 billion per year on energy—about 8% of the $7 trillion annual gross domestic product (GDP). By the middle of the next century, renewable energy is expected to meet a significant fraction, perhaps 50%, of U.S. energy needs. Solar energy, particularly photovoltaic solar cells, could play a central role in renewable energy, especially for electric power generation. It is reasonable to expect that the U.S. solar cell industry could reach $100 billion per year by the middle of the next century.
Although a number of competing sources of renewable energy exist, there are obvious advantages to photovoltaics if costs can be reduced. Solar cells can produce electrical energy at a rate of about 200 kWh/m2 per year (Zweibel, 1990). The current electric energy usage of the United States is 3 billion kWh per year, requiring solar cells covering a land area 120 km x 120 km. With a cost of $150 per square meter of installed solar energy panels and associated infrastructure, including power conditioning and storage, the capital investment in solar energy required to meet current needs is $4.5 trillion. By spreading conversion over 30 years, which is also the approximate lifetime of a panel, the cost would be $150 billion per year. The United States currently spends approximately $200 billion a year on electrical energy; this is about 3% of the $7 trillion GDP per year. For comparison, shipments of photovoltaic modules in 1996 were at the worldwide level of $500 million per year (Strategies Unlimited, 1996). The industry grew 10% in 1996 and was expected to grow 20% in 1997.
There have been steady, incremental reductions in the cost of photovoltaic power over the past 15 years. In quantity, terrestrial solar panels can now be purchased for $4.50 per watt (this figure is for conventional crystalline silicon-based panels.). This represents a decline by a factor of 33 from the 1970 cost of $150 per watt. There have been suggestions that certain manufacturers have an internal cost of production of $2.75 per watt, which is a credit to their streamlining of the manufacturing process. The $4.50 per watt figure translates into a price of about $500 per square meter for solar panels. To provide solar electric power at a cost comparable to the present cost of electricity, silicon solar panels must drop in price by a factor of 5 to 10, if the remaining systems cost is equal to the panel cost (Zweibel, 1990). This is a reasonable expectation in the next 10 to 15 years, given the steep decline noted above and the even more remarkable decline in the cost of silicon electronic devices.
The power output of photovoltaic modules shipped in 1996 was 82.5 MW, divided according to technology as indicated in Table 3.2.
About 4 MW of the thin film figure went to consumer products such as calculators. There have been a number of attempts over the years to replace single-crystal silicon with lower-cost forms such as polycrystalline or amorphous silicon, but the cost advantages are somewhat offset by the reduced efficiency. Through the 1980s, the single-crystal market share dropped from 70 to 40%; it has since recovered to the level shown in Table 3.2.
Silicon photovoltaics are still in a fairly early stage of development as a practical power technology. A number of complex issues surround the various technologies (Partian, 1995; Zweibel, 1990). These include the cost of materials, growth and fabrication of wafers or films,
TABLE 3.2 Market Share of Photovoltaic Technologies for Terrestrial Use, 1996 Shipments
Polycrystalline including ribbon
Source: Strategies Unlimited.
manufacturing technology, and process control. The industry is quite contentious and competitive, which are both healthy signs. The use of silicon by the solar cell industry is approaching 10% of its use by the electronics industry. There have recently been shortages of silicon for solar cells. The sale of electronic-grade silicon is much more profitable for silicon manufacturers than sale of the lower-grade silicon needed for solar cells. There is concern that the portions of boules discarded by chip makers may no longer provide an adequate supply for solar cell manufacturers.
The cost of single-crystal compound semiconductor films, such as GaAs epilayers, is expected to come down in the future. Advanced MOCVD reactors for growing high-quality epitaxial material are now available with growth platters 40 cm in diameter and cycle times of 2 minutes. Several techniques are available for reusing the compound semiconductor growth substrates from these reactors. There are great opportunities for research on solar cells that combine the best of both worlds, high-efficiency and low cost.
Research is being carried out on other solar cell materials such as Culn Se2, CdTe, GaAs, and GaSb. Depending on the material, questions remain concerning issues such as stability and the feasibility of low-cost, large-scale manufacturing. The development of new materials has been and will continue to be a major driving force in solar cell advancements.
Solar Thermal Energy
Of the other forms of solar energy (e.g., wind, hydropower, and so forth) only solar thermal energy uses optics. Solar thermal energy is widely used to provide hot water for domestic and commercial use, process heat for industry and agriculture, and space heating and cooling. With sun-tracking parabolic concentrator mirrors, sufficiently high temperatures can be reached to drive a turbine generator. Using this technology, more than 350 MW generating capacity was installed in the Mojave Desert in the 1980s.
World leadership in optical science and engineering is essential for the United States to maintain its dominance in energy-related technologies such as laser-enhanced fusion, laser uranium enrichment, and solar cells. The Department of Energy should continue its programs in this area.
Summary and Recommendations
Optical Sensors and Imaging Systems
Optical gas sensors are beginning to make a major impact in the field of air quality and pollution emission monitoring and offer real-time quantititative advantages (remote, in situ) over standard chemical analytical techniques. Open-path air monitoring is often used to measure environmental emission levels for compliance with environmental regulations. There are several lidar research programs for global mapping of greenhouse gases and environmental emissions. Lidar is starting to be practical as a commercial instrument, but commercial uses at present are mostly in traffic laser radars, wind shear sensors, and precision range finders and mappers.
Industrial optical chemical sensors are just starting to be used for process control and have shown significant potential in several cases. Optical methods are used in only a minority of chemical sensors, but the fraction is growing as sensors and lasers become smaller and cheaper. Optical biosensors are important trace detectors in the pharmaceutical and medical laboratory industries and are the basis for a wide range of sensitive medical diagnostic tests and DNA sequencing instruments. New photooptical materials, sensitive to specific trace chemicals or biological species, will enable the development of new families of optical sensors.
Satellite-based optical spectroscopic instruments have been used to detect the ozone hole and gases involved in global climate change. Optical and infrared camera sensors in Landsat and weather satellites are used to provide important agricultural and weather data on a daily basis. Future weather and Earth-viewing satellites will be cheaper, smaller, more numerous, and more often commercially financed. Ground-based telescopes using atmospheric compensation and optical interferometric techniques will revolutionize ground-based astronomy at visible and IR wavelengths. Planetary and space probes use optical and microwave sounders to detect and image heretofore unknown chemical species on different planets and have discovered water on the moon.
New high-resolution (high pixel count) optical imaging arrays and CCD video detectors are increasingly used in commercial digital cameras. The most advanced digital cameras have a resolution comparable
to photographic films and are expected to revolutionize and computerize the photographic film and printing industries. New infrared detector arrays are providing improved high-resolution detection of thermal images and will be increasingly used in industry for real-time monitoring of manufacturing lines.
Sophisticated optical and laser sensors are not used to a large degree in forensics and law enforcement because of their cost and lack of portability, but video surveillance and infrared motion security sensors are used extensively. Infrared LED and laser spotlights coupled to IR video cameras are being developed for night vision surveillance. Law enforcement will greatly benefit from advances in materials and systems for IR lasers and room-temperature IR cameras, while decreased size and cost of lasers will increase the use of optical and laser spectroscopic sensors.
Optical sensors are used in many everyday devices, including bar-code readers, proximity switches for water faucets, safety shutoff beams for elevator and garage doors, and new ear-type thermometers for children. Laser printers and fax machines use optical sensors and imaging systems.
Optical sensors are employed in a wide range of important industries and fields and will be an important factor in future industrial growth and competitiveness. However, at present, there is little coordination or information exchange of optical sensor technology between industrial sectors.
DOE, NIST, and industry, in cooperation with the technical and professional societies, should pursue a program to enhance the coordination and transfer of optical sensor technology among industry, academia, and government agencies.
New light sources and delivery systems will offer a large improvement in lighting efficiency. ''White-light LEDs" made by coating a blue LED with a phosphor are now as efficient as incandescent lamps and are expected to become competitive with fluorescent lamps within 5 years. High-efficiency, room-temperature red LEDs are being used in red traffic lights and are expected to save $175 million per year in electrical costs. New light delivery systems, such as plastic fiber cable light bundles and light pipes, are being used in advertisements and other neon-sign-type applications. New materials for light sources, light delivery, and controlled reflectivity have led to increases in lighting efficiency, lifetime, and utility. There is a need for light output measurement standards that account for the response of the human eye and the delivery efficiency of the lighting system.
Laser light shows and optical staging are used in many live performances, although they are often considered secondary in importance
to the performance itself. The annual market for lasers and optics for laser light shows and live performances is steady.
New high-efficiency lighting sources and light distribution systems will have a significant impact on the country's electricity use. There is only moderate coordination of research and standards setting on new, efficient, and effective lighting sources among government, academia, and industry.
DOE, EPA, EPRI, and NEMA should coordinate their efforts and create a single program to enhance the efficiency and efficacy of new lighting sources and delivery systems, with the goal of reducing U.S. consumption of electricity for lighting by a factor of two over the next decade, thus saving about $10 billion to $20 billion per year in energy costs.
Optical Sensors and Lighting in Transportation
With the exception of fiber-optic gyroscopes, optical sensors are not used extensively in aircraft, where they do not yet offer advantages over conventional mechanical or electrical sensors.
Optical sensors and lighting are used to a great extent in automobiles, where they play an integral and important role. New high-efficiency headlamps, LED taillights, and optical collision avoidance systems are being introduced into automobile lines.
The world's largest laser and optical systems are being developed for nuclear energy-related programs. The National Ignition Facility will be the largest sophisticated optical system in the world and a major new research tool for the United States. The AVLIS program will provide economical separation of uranium reactor fuel.
Solar cell efficiency has increased and cost may have decreased to $2.75 per watt. A decrease of a factor of 5 to 10 in solar cell cost would make the price of solar photovoltaic electrical energy comparable to that for nonrenewable sources. If the cost of solar photovoltaic cells continues to decline, solar cells could begin to impact the electric power industry by 2020 and could provide as much as half the world's electric power by 2050. As a source of renewable energy with low environmental impact, efficient, low-cost solar energy could have a great impact on world energy consumption. If successful, such programs could have a significant effect on future energy programs and the cost of energy in the United States.
World leadership in optical science and engineering is essential for the United States to maintain its dominance in energy-related technologies such as laser-enhanced fusion, laser uranium enrichment, and solar cells. The Department of Energy should continue its programs in this area.
American Chemical Society. 1996. Technology Vision 2020: The U.S. Chemical Industry. Washington, D.C.: American Chemical Society.
Bruton, T.M., et al. 1997. Multi-megawatt upscaling of silicon and thin film solar cell and module manufacturing. Paper presented at the European Community Photovoltaic Conference, Barcelona, June. (Author's address: BP Solar, P.O. Box 191, Sudbury-on-Thames, Middlesex TW16 7XA, United Kingdom.)
Herkströter, C.J.A. 1997. Speech at Erasmus University, Rotterdam, March 17. Available from Shell Oil Company, 712 Fifth Avenue, New York, NY 10019.
Janata, J., M. Josowicz, and D.M. DeVaney. 1994. Chemical sensors. Anal. Chem. 66:207.
Lindl, J., R. McCrory, and E.M. Campbell. 1992. Progress toward ignition and beam propagation in inertial confinement fusion. Phys. Today (September):32.
Menzel, R. 1989. Detection of latent fingerprints by laser excited luminescence. Anal. Chem. 61:557a.
National Research Council. 1993. Counterfeit Detection Features for the Next-Generation Currency Design. Washington, D.C.: National Academy Press.
Office of Technology Assessment. 1990. Technology for a Sustainable Future. Washington, D.C.: U.S. Government Printing Office.
Partian, L.D., ed. 1995. Solar Cells and Their Applications. New York: Wiley.
Rea, M., ed. 1993. The Illumination Engineering Society Lighting Handbook. New York: Illumination Engineering Society of North America.
Rogers, K.R., and C.L. Gerlach. 1996. Environmental biosensors: A status report. Environ. Sci. Technol. 30:486A.
SPIE. 1996a. Physics Based Technologies for the Detection of Contraband. Conference No. 2936. Boston: SPIE Conferences.
SPIE. 1996b. Chemistry and Biology Based Technologies for the Detection of Contraband. Conference No. 1937. Boston: SPIE Conferences.
Strategies Unlimited. 1996. Five-Year Photovoltaic Market Forecast: 1995-2000. Report PM-43. Strategies Unlimited, 201 San Antonio Circle, Suite 205, Mountain View, CA 94040.
Vo Dinh, T., K. Houck, and D.L. Stokes. 1994. Surface enhanced Raman gene probes. Anal. Chem. 33:3379.