Opportunities in Intense Ultrafast Lasers Reaching for the Brightest Light (2018) / Chapter Skim
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6 Applications
6 Applications
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From page 126... ...
In manufacturing, for example, robotic lasers have been programmable in a way that mechanical cutting tools had not been, with the same factory floor laser station capable of cutting, drilling, measuring, and in some cases welding and peening. High-intensity short pulse lasers, in particular, have unique capabilities for precision, mainly due to minimal thermal energy deposition in materials, resulting in negligible collateral damage beyond the desired interaction volume.
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Figure 6.1 depicts laser processing activities as a function of the laser pulsewidth.3 Femtosecond laser processing for materials manufacturing is expanding as robust commercial lasers become available. Typical operating parameters for com mercial lasers used for manufacturing include pulsewidths of 100-200 fs, peak 1 Photonics21, "2020 Photonics Roadmap," accessed January 8, 2017, http://www.photonics21.org/ download/Brochures/Photonics_Roadmap_final_lowres.pdf.
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energies of 50-150 µJ, average powers of 100-150 W, and pulse repetition rates up to 1 MHz.4 Table 6.1 shows a list of 20 global industrial laser companies whose short-pulse lasers range in pulsewidth from <6 fs to ~1 ns. High-intensity femtosecond laser processing is considered a "cold" process since the substrate does not heat during the interaction.5 The physical mechanism used in material removal is plasma formation leading to ablation rather than melt ing.
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: 195422, doi:10.1103/ PhysRevB.72.195422. 8 Max Groenendijk, "Fabrication of Super Hydrophobic Surfaces by Fs Laser Pulses," Laser Technik Journal 5, no.
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Femtosecond laser ablation depths from a single laser pulse can be more precise than material removal with conventional laser melting, as shown in Figure 6.2.12 Cracks due to thermal damage are present at picosecond to femtosecond pulses but nearly disappear when the pulse duration is reduced to 5 fs.13 Since thermal damage and stress-induced cracking depends on the average power of the femto second laser source, absorbed laser power leads to melting or thermal shock even with picosecond or femtosecond pulse duration. Other ultrashort pulse laser applications that have been studied and reported for industrial processes include higher peak power femtosecond pulses to help to improve the resolution of the laser-induced breakdown spectroscopy (LIBS)
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Fekete, and T Mocek, Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown, Scientific Reports 6:39133, 2016.
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. For example, temporally resolved radiography could be used to diagnose the evolution of the fuel compression of an inertial fusion implosion, strong shock propagation in materials, evolution of hydrodynamic i nstabilities in accelerated targets, and other high energy density physics experi 16 Dongkyun Lee and Elijah Kannatey-Asibu, "Experimental Investigation of Laser Shock Peening Using Femtosecond Laser Pulses," Journal of Laser Applications 23, no.
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ARC's short, wide bandwidth, 1-µm light laser pulses propagate down the existing National Ignition Facility (NIF) beamlines.
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In addition, high-intensity short-pulse lasers can be used to create radiation (both photon and particle) that can be used to interrogate systems and identify the presence of nuclear or chemical materials of concern for proliferation or homeland security.20 Such lasers could have some advantages over alternative technologies, but must be capable of both high intensity and average power.21–2321-2 3 Programs 20 Sudeep Banerjee et al., "Compact Source of Narrowband and Tunable X-Rays for Radiography," Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 350 (May 1, 2015)
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, which uses ultrafast laser scalpels to make incisions in the eyeball as part of a laser sculpting protocol to improve eyesight.24 These laser methods use some of the materials-processing benefits of high-intensity laser matter interactions, such as reduction of collateral damage due to heating; but the lasers themselves are small-scale instruments because peak power is limited by the microscopic nature of this kind of surgery. This section will have a primary focus on medical applications that require the use of high peak power lasers that are capable of ultrahigh intensities.
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6.4.2 Electron Beams for Cancer Therapy Radiotherapy seeks to selectively kill cancer cells by breaking off the caps at the end of their deoxyribonucleic acid (DNA) chains without doing too much damage to healthy cells.
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. Early laser-proton radiotherapy research began in 1998 in a collaboration between Stanford and LLNL;32 it was 10 years before beams containing high-current, ultra-short pulses of protons accelerated by ultra-short, ultra-intense lasers, produced biological effects.33 Experiments showed that ultra short bunches of high-energy protons produced by lasers were equally efficient in killing cancer cells as synchrotron-produced proton beams.34 6.4.4 Laser-Produced Isotopes for Positron Emission Tomography The well-known medical procedure of PET currently requires the nearby pres ence of a synchrotron/cyclotron to create the short-lived radioactive sources that provide the positrons.
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systems, as key to achieving a compact laser-ion beam radiotherapy facility: "Enroute it is critical now to demonstrate the comprehensive need for laser-driven energetic ions; including applications that might require only the emergent ion ‘spray' (or have minimal ion optics requirements)
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, and relaxed symmetry requirements because ignition does not depend on uniform compression to very high densities. The fast ignition concept for inertial confinement fusion was proposed with the emergence of ultrahigh-intensity, ultrashort pulse lasers using CPA.42 The target compression can be done by a traditional ICF driver (direct-drive by lasers or ion beams, or indirect drive from X-rays using a hohlraum driven by nanosecond lasers, ion beams, or a Z-pinch)
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Johnson, et al., 2001, Fast ignition by intense laser-accelerated proton beams, Phys.
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6.6 DOD SECURITY APPLICATIONS 6.6.1 Ultrashort Pulse Applications The following applications of ultra-short-pulse lasers have been considered by the Navy:49 • Long range directed energy, exploiting nonlinear focusing to overcome dif fraction. This could include both direct target damage or target "softening" for a high-energy laser attack.
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In another development, it was shown that rather than carrying significant beam energy itself, a multi-filamenting ultrashort pulse laser could imprint long-lasting waveguides in the atmosphere that can guide auxiliary high energy and high average power laser beams.55 6.7 EXTREME NONLINEAR OPTICS: HIGH-ORDER HARMONIC GENERATION An area of high-intensity laser science with high potential impact is the gen eration of coherent short-wavelength (extreme ultraviolet [XUV] to soft X-ray)
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Christov, 1996, Enhanced high harmonic generation using 25 femtosecond laser pulses, Physical Review Letters 76(5)
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Zhao, and Z Chang, 2009, Generation of isolated attosecond pulses with 20 to 28 femtosecond lasers, Physical Review Letters 103(18)
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Holtsnider, R.I. Tobey, et al., 2007, Lensless diffractive imaging using tabletop coherent high-harmonic soft-x-ray beams, Physical Review Letters 99(9)
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74 European Semiconductor Industry Association, Japan Electronics and Information Technol ogy Industries Association, Korean Semiconductor Industry Association, Taiwan Semiconductor Industry Association, and United States Semiconductor Industry Association, 2013, International Technology Roadmap for Semiconductors, http://www.itrs.net/Links/2013ITRS/Home2013.htm, ac cessed March 14, 1017.
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Andriukaitis, T Balčiunas, et al., 2012, Bright coherent ultrahigh harmonics in the keV x-ray regime from mid infrared femtosecond lasers, Science 336(6086)
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