Opportunities in Intense Ultrafast Lasers Reaching for the Brightest Light (2018) / Chapter Skim
Currently Skimming:
5 Science Motivation
5 Science Motivation
Pages 85-125
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 85... ...
The high-intensity laser research opportunities described in this chapter cannot all be realized with only one type of large laser facility. Petawatt lasers configured to study particle acceleration are not optimized to excite or probe high density matter, for example.
|
From page 86... ...
Figure 1.3 in the introductory chapter of this report, reproduced here for convenience, describes the regimes of extreme field physics associated with the historical development of technology for high peak power lasers. The threshold laser intensity for entrée to each regime is set by parameters that characterize the laser and physical system that describe the interaction.
|
From page 87... ...
UP is proportional to I λ2, where I is the laser intensity and λ is the laser wavelength. This is also shown in Figure 1.3, for laser wavelengths on the order of 0.8-1.0 microns, the most common wavelengths used for petawatt lasers.
|
From page 88... ...
. This intensity regime opens up the field of relativistic nonlinear optics, which includes applications in laser-driven particle acceleration3 and short wavelength radiation sources.4 Extreme fields can also arise as secondary sources from intense laser-matter interactions -- in particular, as a consequence of bright relativistic electron and ion beams generated through laser-gas and laser-foil in teractions.
|
From page 89... ...
Norreys, 2006, Using high-power lasers for detection of elastic photon-photon scattering, Phys.
|
From page 90... ...
Current sources of laser-driven attosecond pulses and pulse trains made from these interactions have been demonstrated over 10-150 eV XUV photon energy range with 108 to 1010 photons per pulse10 and 1-2 keV range with 104 to 105 photons per pulse.11 The repetition rate of these sources is tied to the laser repetition rate and varies from ~10 Hz to 10 kHz, corresponding to ~µW average power. Current sources can drive linear absorption processes, but current pump-probe arrange ments rely on a reference strong field, usually the fundamental femtosecond laser field, to initiate and drive nonlinear dynamics in matter.
|
From page 91... ...
Figure 5.2 summarizes the history and future of ultrafast pulse generation driven by high-intensity lasers. 5.2.2.1 Attosecond Response of Matter Driven by High-Average Power Lasers All stable matter is held together by electrons, whose mass (m=9 × 10–31kg)
|
From page 92... ...
Bingham, and P.A. Norreys, 2015, Compres sion of x-ray free electron laser pulses to attosecond duration, Scientific Reports 5: 16755.
|
From page 93... ...
interaction.16 5.3 HIGH-INTENSITY PETAWATT LASER STUDIES OF HIGH ENERGY DENSITY SCIENCE, PLANETARY PHYSICS, AND ASTROPHYSICS Laboratory-based experiments that create and explore extreme states of mat ter characterized by high density, temperature, and pressure -- high energy density science -- are the only terrestrial means for addressing issues relevant to the phys ics of planetary interiors, for example. High energy density science (HEDS)
|
From page 94... ...
17 R.W. Lee, 2007, High Energy Density Science at the Linac Coherent Light Source, Lawrence L ivermore National Laboratory, UCRL-TR-236300.
|
From page 95... ...
5.3.1 Planetary Physics and Astrophysics For planetary physics, understanding the equation-of-state of extreme matter stands as a central challenge.18 The interiors of giant planets exist in a pressure/ temperature regime where accurate equation-of-state calculations are extremely difficult. Understanding chemistry under these extreme conditions is particularly challenging because molecules, atoms, and ions coexist in a fluid that is coupled by Coulomb interactions and is highly degenerate (free electrons governed by quan tum and thermal effects)
|
From page 96... ...
Hence the internal structure and the magnetic fields of giant planets are determined by knowledge of the equation-of-state at high pressures, 1011 - 1013 pascal. Calculations based on first-principles theories are extremely difficult and inaccurate.
|
From page 97... ...
An open question is whether there is a sharp plasma phase transition. Experiments performed on the Nova laser at LLNL initially suggested that the transition was continuous,28 and subsequent experiments unambiguously demonstrated that the transition from non-conducting molecular hydrogen to atomic metallic hydrogen at high pressure is a continuous transition.
|
From page 98... ...
: 1178-1181. explain why the magnetic field of Jupiter is so much stronger than that of the other planets of our solar system.29 A supernova (SN)
|
From page 99... ...
.35 Magnetic fields in astrophysics. Strong magnetic fields play an important role in a number of astrophysical processes such as solar flare generation and conver 31 W.D.
|
From page 100... ...
kinetic energy.36 PW-class studies of ultra-high magnetic field generation and interactions can address important questions such as whether magnetic fields affect cosmological structure formation and how strong magnetic fields originated in the universe. 5.3.2 Isochoric Heating and High Energy Density Plasmas The study of the material properties of matter uniformly heated to extreme pressures is of interest for basic studies of strongly coupled plasmas, degenerate and non-degenerate warm dense matter, and the understanding of high density plasmas characteristic of inertial confinement fusion experiments and defense applications.
|
From page 101... ...
Aside from its relevance to theo retical models of condensed matter physics in extreme conditions, the study of dense hydrogen is directly relevant to an understanding of planetary interiors and stars (as discussed in Sec 5.3.3) and fusion plasmas.47 Intense heating using a combination of laser pulses can generate hydrogenic plasmas at variable density and temperature, allowing exploration of various phases and their electronic and structural properties, potentially including the long sought after metallic hydrogen state.48 Such targets can be probed, for example, using short LCLS X-ray pulses to measure density, temperature, conductivity, ion-ion correlations, structure factors, and transport coefficients using both collective scattering (coherent Thomson scattering)
|
From page 102... ...
For this reason, the co-location of ultrashort high-intensity lasers and X-ray FELs is particularly advantageous for such experiments. 5.3.3 Science That Combines X-ray Free-Electron Lasers, High Energy Electron Accelerators, and Petawatt-Class Lasers X-ray FELs are high-intensity light sources of a special nature that can be used for unique science tasks related to their short wavelength (see Chapters 1 and 2, Section 5.2, and Section 5.7)
|
From page 103... ...
5.4 PETAWATT LASER-DRIVEN PARTICLE ACCELERATORS 5.4.1 Particle Acceleration and Particle Physics Particle accelerators driven by intense, short pulse lasers are in development for the purpose of a new technology of ultra-high gradient devices that occupy a much smaller footprint than conventional machines. A primary limitation of conventional charged particle accelerators for particle physics and higher intensity sources is their size and the associated costs of large conventional machines.
|
From page 104... ...
Conventional charged particle accelerators have already enabled the development of coherent and incoherent high energy photon sources having application to basic science, engineering, and medicine. Laser-driven high-energy accelerators make possible a new generation of such light sources on a much more compact scale (meter scale)
|
From page 105... ...
SOURCE: M Tigner, 2001, Does accelerator based particle physics have a future?
|
From page 106... ...
The plasma wave is created as the laser pulse propagates in subcritical density plasma generated in a gas jet or in a plasma discharge, using high-intensity optical guiding using pre-formed plasmas64 or self-guiding.65 The enormous axial electrostatic field of the plasma wave, which propagates with the group velocity of the laser pulse, can accelerate electrons ex ternally injected or self-injected from the plasma background by wave-breaking or ionization injection.66 Relativistic electrons injected with the proper phase can be accelerated and focused by the wakefield. Figure 5.6 illustrates a LWFA.
|
From page 107... ...
Both of these limita i tions point to the need for high energy/intensity lasers: high energy pulses counter balance depletion and drive large amplitude plasma waves over long propagation distances especially at low plasma densities where dephasing is minimized. Using a PW-class laser, the Berkeley Lab Laser Accelerator facility at Lawrence Berkeley National Laboratory has reported a record 4.2 GeV electron beam in single 10 cm plasma channel, with 10 GeV in 1-meter appearing feasible.67 Achieving even higher beam energies requires a "staging" of many laser-plasma acceleration modules in order to mitigate depletion and dephasing.
|
From page 108... ...
69 W.P. Leemans, 2010, White Paper of the ICFA-ICUIL Joint Task Force -- High Power Laser Tech nology for Accelerators, http://icfa-bd.kek.jp/WhitePaper_final.pdf.
|
From page 109... ...
5.5 INTENSE LASER-DRIVEN PARTICLE SOURCES OF ENERGETIC PHOTONS, NEUTRONS, AND POSITRONS The generation of short, high flux pulses of energetic photons, neutrons, and positrons by intense laser interaction with matter offers new and unique oppor tunities in scientific, engineering, and medical imaging. Applications in materials processing and in radiography both call for intense and bright sources of X-rays, positrons, protons, and neutrons that can be supplied by intense lasers.
|
From page 110... ...
Directing laser-plasma accelerated electron bunches into a high-Z dense mate rial to produce short pulses of bright, forward directed γ-rays via bremsstrahlung radiation.73 Photon energies are typically > 1MeV, depending on the energy of the laser accelerated electrons.
|
From page 111... ...
reaction in low-Z foil targets, such as Be.75 Such neutron beams can be used as passive or active material probes, including hidden contra band materials. A second method under study is generation of bremsstrahlung γ-rays from stopping of laser-accelerated electron beams in high-Z targets followed by neutron emitting (γ n)
|
From page 112... ...
: 105001. 81 Hui Chen et al., "Relativistic Positron Creation Using Ultraintense Short Pulse Lasers," Physical Review Letters 102, no.
|
From page 113... ...
γ-ray beams are made by scattering a laser beam off an electron beam; through the incoherent Compton scattering process, energy from the scattered electron is transferred to the scattered photon. The energy of the scattered photon depends upon the energy of the electron beam, the scattering angle, and the wavelength of the laser beam.
|
From page 114... ...
These laser beams can distort the properties of the vacuum, probing its properties such as vacuum birefringence. Laser fields can also be controlled to minimize (or eliminate)
|
From page 115... ...
: 1159–64, doi:10.1007/ s12043-007-0247-6. 86 Bamber et al., "Studies of Nonlinear QED in Collisions of 46.6 GeV Electrons with Intense Laser Pulses." 87 G
|
From page 116... ...
A listing of these is given below. 5.7.3.1 Schwinger Critical Field Exceeded in Laser Collisions with Relativistic Electrons In its current configuration, the SLAC linear accelerator in Menlo Park, C alifornia, operates as three 1-km linear accelerators, two of which are capable of producing ~ 15GeV electrons (γ = 30,000)
|
From page 117... ...
Bell and J.G. Kirk, 2008, Possibility of prolific pair production with high-power lasers, Phys Rev Letters 101(20)
|
From page 118... ...
Roughly 100 positrons were detected and attributed to the cooperative interaction of laser photons with a backscattered Compton gamma ray. 5.7.3.5 Spin Polarization Pair production by a high-energy photon and a strong laser field show differ ences between boson and fermion pair production in an oscillating electric field and also show that the existence of a fermionic (bosonic)
|
From page 119... ...
"Complete QED Theory of Multiphoton Trident Pair Production in Strong Laser Fields." Physical Review Letters 105, no.
|
From page 120... ...
Thomson and Compton scattering have been theoretically considered many times in the literature. One recent description of multiphoton Compton scattering accounted for the electron and photon polarizations,101 while others have evaluated the effects of finite, even ultrashort, pulse duration on multiphoton Thomson and Compton scattering.102 For this latter consideration, the main differences with re spect to the monochromatic case are a broadening of the lines, corresponding to the emitted frequencies, and the appearance of sub-peaks, due to interference between emission from the front and back ends of the laser pulse.
|
From page 121... ...
Since high-energy photons can be emitted via Thomson and Compton scat tering, these processes have been of interest for producing short wavelength radia tion. The main advantages of these sources compared, for instance, to synchrotron sources, are their compactness, wide tunability, short pulse durations (femtosecond or shorter)
|
From page 122... ...
Nees, and G.A. Mourou, 2010, Pair creation in QED-strong pulsed laser fields interacting with electron beams, Phys.
|
From page 123... ...
5.7.6.1 Vacuum Birefringence One way to observe vacuum polarization effects is to detect their influence on the polarization properties of a probe electromagnetic beam. Within the frame work of QED, the vacuum can be a birefringent medium due to the presence of a "background" electromagnetic field.
|
From page 124... ...
These particles could either be very heavy and therefore appropriate for large-scale accelerator experiments, or they could be light and weakly charged, so-called minicharged particles, well suited for laser-based searches.117 Vacuum nonlinearities associated with minicharged particles may be observ able in a strong external laser field, modifying the vacuum birefringence effects expected within the Standard Model (i.e., deviations from QED predictions would be observed) .118 Analysis indicates that strong field vacuum birefringence experi ments could significantly improve existing experimental constraints on minicharged particles in the mass range below 0.1 eV.
|
From page 125... ...
5.7.7.4 Unruh Radiation Intense lasers can rapidly accelerate electrons and it has been suggested that high-intensity lasers could achieve accelerations comparable to those experienced in the vicinity of a black hole.121 Such rapidly accelerated electrons are expected to emit Unruh radiation. This may be useful in exploring as yet unresolved issues associated with the Hawking radiation predicted to arise near a black hole event horizon.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.