Lasers are sources of coherent electromagnetic radiation projected in nearly collimated beams and produced by the process of quantum stimulated amplification. This electromagnetic radiation travels through vacuum at the speed of light c, about 30 billion cm/s, and consists of waves of oscillating electric and magnetic fields with wavelengths that range from fractions of a millimeter for far infrared sources, to fractions of one micron for visible lasers, to angstroms for X-ray lasers. In transparent media such as air or glass, the radiation travels more slowly than the speed of light in vacuum. The electric field of the light oscillates, but is usually characterized by its peak value. In the standard “SI” system of units used in physics, the units of field amplitude are volts per meter. The field also has a direction in space called the “polarization” of the light that is usually perpendicular to the direction of the light propagation. Polarization can be linear, but it can also be circular or elliptical, in which case the electric field oscillates in direction as well as amplitude.
Laser beams may be bright or dim, may exist at visible or invisible wavelengths, may contain a narrow or a broad range of wavelengths, and may be more or less divergent. This study concerns some of the brightest lasers, those with the highest peak power, which can deliver the highest intensity radiation. Power is the rate of energy flow in the laser beam, measured in watts. Average power is power averaged over some relevant time interval.
Peak power is the instantaneous power, usually at the peak of a laser pulse, also measured in watts. A typical laser discussed in this study may have an average power of only a few watts but could have a peak power as high as 10,000 trillion watts (10 petawatts, 1016 watts). The pulse energy is the integral of the power over the pulse duration, measured in joules. The cost of a laser tends to scale with the pulse energy rather than the peak power.
Pulse Repetition Rate
Pulse repetition rate is another important criterion. Petawatt lasers do not generally pulse at high rate, but rather they store energy and then release it in a “single shot.” Many other types of lasers have less per-shot energy but achieve high average power through high pulse repetition rates.
Intensity is power per unit area, usually at the waist, or narrowest part, of a focused laser beam, usually measured using the mixed unit Watts/cm2. As with power, intensity may also be expressed as peak or average intensity. This study defines high intensity as intensities that will field ionize matter (i.e., ~1014 W cm–2) and ranges up through ultrahigh intensity. The highest currently-accessible peak laser field intensities are approximately 10-billion-trillion Watts/cm2, 1022 Watts/cm2. To put this in some context, the temperature that corresponds to this radiation intensity is 200 million degrees. This is about ten times the central temperature of the sun and 40,000 times the surface temperature. Thus it represents a unique laboratory for fundamental scientific studies.
Peak Field Strength and Vector Potential
The intensity I is related to the amplitude of the oscillating electric field strength E of the electromagnetic radiation that makes up light. The connection is , where c is the speed of light, ε0 is the vacuum permittivity, and n is the index of refraction of the medium.
As shown, the peak field strength of the laser beam scales as the square root of the intensity. When the intensity is 1022 Watts/cm2, the peak electric field is about 3 trillion volts per centimeter, which is 600 times greater than the field strength that binds the hydrogen atom (5×1011 V/m) and nearly an order of magnitude higher than the binding field of any atomic electron in nature.
The relationship between the field amplitude E and the electromagnetic vector potential amplitude A is given in SI units by and in Gaussian units by . Physically, the vector potential is proportional to the momentum that a charged particle acquires due to the force exerted by the field. In high-intensity laser physics one often encounters the normalized vector potential a, which is the vector potential in units of mc, where m is the electron mass and c is the speed of light.
Pulse Length and Duration
A third important quantity for high-powered lasers is pulse length and duration, which may be as short as a few cycles—a few microns for visible laser light, corresponding to a pulse duration of a few femtoseconds—or as long as a meter, corresponding to three nanoseconds duration. Shortening the pulse duration has always been an important goal for high-intensity laser science because for fixed pulse energy, the peak power increases when the duration of the pulse decreases. The most intense pulses referred to in the previous paragraphs have pulse durations on the order of 30 femtoseconds, or about 10 cycles for a wavelength of 1 µm. The science chapters of this study will also describe efforts to produce pulses shorter than 1 femtosecond, in the attosecond range, which requires wavelengths in the ultraviolet or vacuum ultraviolet range. This is relevant since the generation of attosecond pulses is possible only through the application of high-intensity (femtosecond) pulse lasers.
Two additional properties of a laser are its spatial and spectral coherence, equivalently called transverse and temporal coherence. These have mathematical definitions as correlations between the light field at different points in space and time, respectively. For pulsed lasers, where the light field is a compact nearly monochromatic pulsed beam of light with an approximately Gaussian spatial and spectral profile, the best possible spatial coherence will lead to a focus with the smallest waist and therefore the highest intensity. This optimal focus is called the “diffraction limit,” where the focal waist radius w of a focused beam with focal convergence angle Δθ and wavelength λ has its minimum value w~2λ/π Δθ. There is a similar limit in the time domain. Short laser pulses cannot be purely monochromatic because of the well-known spectral uncertainty principle: The shortest and therefore most intense possible pulse Δτ for a spectral spread Δf is called the “Fourier transform limit,” given by the spectral time-bandwidth product of ΔfΔτ~1/2.
Finally, another relevant parameter is the wavelength of the light λ, which is directly related to the light frequency ν = c/λ, the angular frequency ω = 2πν, and the photon energy hν. Here c is the vacuum speed of light and h is Planck’s constant. The light matter interaction often differs substantially depending on the wavelength of the light. Currently, high intensities as defined above can be generated at wavelength ranging from the deep-UV (~250 nm) to the mid-infrared (~4 µm) and beyond, with the vast majority of work starting in the near-infrared at either 800 nm (Ti:sapphire) or 1 µm wavelength (neodymium-based solid-state lasers). In recent years, as the physics at these wavelengths has become more-thoroughly explored, physics near the wavelength boundaries (far-IR and deep-UV) has seen an uptick in interest. Further, X-ray free-electron lasers, by virtue of the superior focusability and sub-femtosecond pulse duration that comes from their sub-nanometer wavelength, can reach comparable high intensities with only hundreds of gigawatts to terawatts of peak power rather than petawatts. These have a different science impact, though, because of photon energies in the kilo-electron-volt range instead of the electron-volt range of visible lasers.
Laser pulses cannot turn on and off instantaneously because the uncertainty principle limits the minimum time-bandwidth product to 0.5. In addition, amplified laser pulses nearly always contain a temporal pedestal much longer than the central peak due to the gain dynamics. This becomes important in high-intensity laser matter interactions, where damage to the target may be induced by the pedestal long before the central peak arrives. The figure of merit for this is the “contrast ratio,” defined as the ratio of peak intensity to pedestal intensity in a laser pulse.
The first demonstration of a laser in 1960 by Maiman in the United States attracted considerable attention as the first spectrally narrow (i.e., temporally coherent) optical frequency source. Perhaps more intriguing about the laser was its much higher spatial coherence than other sources of light, meaning that it could travel long distances as a narrow beam and could be focused by a lens or a mirror to a much smaller diameter than prior light sources, approaching the diameter equivalent to the wavelength of the light. Even modest powers from the laser could produce focused intensities well beyond what had been produced by any other light source or from powerful microwave sources developed for radar applications. Early laser demonstrations used focused power to drill through steel and gave way to more important uses in precision eye surgery and micro-machining of materials.
Subsequent developments of laser technology of interest for this study involved concentrating the energy into a shorter pulse. An early breakthrough in this direction was Q-switching, a means developed in the 1960s to store energy in the gain medium over a long time and then extract it as laser energy over a short time. This led pulse durations on the order of the time for light to make a round trip in the laser cavity, generally 5 to 10 nanoseconds. With this, even modest pulse energies, on the order of 1 Joule, yielded instantaneous (peak) powers of 100 MW, and the intensity of light at the focus could approach 1015 W/cm2. This is equivalent to a temperature of over 3 million degrees and therefore suggested to some that lasers could be used to investigate nuclear fusion.
The Department of Energy funded programs over several decades to study fusion with large amplified Q-switched laser pulses, culminating in 2009 with the multi-billion-dollar National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, presently the world’s most energetic laser, with 4 MJ total pulse energy. The NIF combines the pulses from 192 separate beam lines, each employing Nd-doped glass amplifiers of 3 ns Q-switched laser pulses. The combined peak power exceeds 1 × 1015 W (1 Petawatt), achieved through combining many lasers. The NIF amplifiers are large-scale modern implementations of a basic architecture that was developed in the 1960s: relatively inefficient Xe gas discharge lamps excite a rare-earth doped glass gain medium. The thermal characteristics of glass lead to a low repetition rate of ~ one pulse per hour.
Another important breakthough for high-power lasers is mode locking. This is a method of gain modulation just as is Q-switching, but in mode locking the modulator changes the gain in sync with the round-trip light travel time in the cavity. The laser energy takes the form of a very short pulse, which passes through the mode locker during its point of maximum transmission on every round-trip through the cavity. The shortest pulse possible is set by the frequency range over which a given laser material provides amplification (the laser gain bandwidth). This can be as short as 10 femtoseconds for some gain media such as Ti:Sapphire. For the case of Nd:glass, the shortest pulse is a fraction of a picosecond. There are many physical methods for mode locking, but a particularly useful method is Kerr-lens mode locking, which uses the nonlinear interaction of the light with the gain medium host (glass or sapphire, typically) to stabilize mode-locked short pulses in the cavity.
Mode-locked amplified pulses should in principle be scalable to enormous peak power but a critical limitation is the damage resistance of the lasing medium itself. Picosecond or femtosecond pulses with sufficient intensity to efficiently extract energy from Nd:Glass or Ti:Sapphire will also destroy the glass or the sapphire through the process of dielectric breakdown—literally forming a spark that destroys the material. The breakthrough that resolved this limitation is chirped-pulse amplification (CPA), which is based on an idea from high-powered radar systems. The CPA concept for laser amplification was first implemented by Mourou and Strickland at the University of Rochester in the 1980s.
With CPA, the short mode-locked pulses pass through special-dispersive optics where the optical path length depends on optical frequency. This stretches the pulse length by as much as 1,000-30,000 times, thereby reducing the peak power by the same factor. Further amplification then uses a laser system similar to Q-switched amplifiers. At the output of the final amplifier, the energetic pulse is compressed in time by another set of optics to reverse the stretching. Typically the compression optics include a set of large-aperture gratings, up to 1 meter in size.
In 1996, the CPA technique was applied to a Nd:glass laser system to build the first single-beam, PW-peak power laser, with about a 0.5-ps pulsewidth, notable in that the peak power was of the same order as the entire NIF laser. Subsequent development of Nd:glass CPA systems, involving optimization of the laser gain bandwidth, has allowed operation with pulses as short as about 0.15 ps.
Broadly tunable lasers based on other solid-state media, most notably titanium-doped sapphire (Ti:sapphire), have properties well suited for energy and hence peak-power scaling. In mode-locked operation, the extremely large linewidth of
the Ti:sapphire laser, centered around 800 nm, allows generation of pulses as short as 5 fs. The most common pumping source is another laser, and the relatively long storage time enables energetic pulse amplification when the pump source is a pulsed laser with sub-microsecond pulsewidth, most often a Q-switched solid-state laser.
Typical CPA Ti:sapphire lasers operate with 20 to 30 fs pulses, allowing for increasingly compact tabletop TW-scale lasers with diffraction limited focusability to generate even relativistic intensities on a tabletop, and PW-class lasers with about 5 to 7X lower pulse energies than Nd:glass CPA systems. Another important difference from Nd:glass systems is that the thermo-mechanical properties of the sapphire (Al2O3) crystal are much better compared to the oxide glasses used in high-energy systems, allowing Ti:sapphire to operate at pulse rates limited by the pump laser, and PW-class Ti:sapphire systems to operate at pulse rates of 1 to 10 pulses/sec, compared to the pulse/hour rate for energetic glass lasers.
Commercial Chirped-Pulse Amplification Lasers
Many aspects of the high-intensity physics phenomena of interest in this report have been developed using commercialized, tabletop-scale weaker (i.e., terawatt) CPA lasers for research, rather than the large petawatt-class lasers that are the focal point of this study. Terawatt lasers can be scaled to repetition-rates in the kHz range. These typically cost under $1 million and are therefore affordable for university programs. Small specialty laser companies, such as KMLabs, and larger research laser companies, such as the European Thales Group and the American-based Coherent Radiation or Newport-Spectra, serve this market. Thales also markets custom PW laser systems, as does a small start-up, Austin-based Laser Energetics, but these are only affordable on a regional or national scale.
Optical Parametric Chirped-Pulse Amplification
At present, CPA PW-class lasers are primarily either Ti:sapphire- or Nd:glass-based, but a new technology has emerged that allows nanosecond pump lasers to convert their energy efficiently to chirped pulses comparable to CPA Ti:sapphire lasers. The approach, optical parametric chirped-pulse amplification (OPCPA), utilizes nonlinear parametric frequency amplification. An OPCPA is a parametric amplifier, not a laser. The difference is that a laser amplifies light in a two-step process: First, the gain medium is excited by some energy source; later, the energy is extracted from the gain medium by stimulated emission. A parametric amplifier converts energy from the excitation source directly into the output laser in a single step. The host medium is just a converter; it does not need to store the energy. In the case of an OPCPA, the host medium converts an energetic narrow bandwidth nanosecond laser into a broad bandwidth chirped laser pulse that can be compressed later to create a high peak power. To date, work in Russia has demonstrated a 0.56 PW system (25 J in 45 fs) and a longer pulse 1 PW device (100 J in 100 fs). These high-energy results employ Nd:glass lasers as pump lasers and thus have the same low pulse rates as Nd:glass-based CPA systems, but as the technology of energetic nanosecond lasers advances, OPCPA systems can be expected to advance in performance as well.
Intense X-ray Free-Electron Lasers
Free-electron lasers (FELs) can produce comparable high intensities to petawatt lasers but with much lower (sub-terawatt) peak power and much shorter (sub-nanometer) wavelength. They utilize ultrarelativistic intense electron beams as a gain medium, produced in long traveling-wave radio frequency accelerator structures located at large national accelerator laboratories in the United States, Europe, and Japan. These facilities are quite expensive, on the order of $1 billion.
X-ray FELs do not employ optical CPA, but they do employ chirped pulse methods for the electrons in the accelerator. The electron bunch is chirped in an accelerating structure quite analogous to the fiber disperser that was used in the original implementation of CPA. The long chirped electron bunch is then accelerated and compressed to a short pulse with high peak charge density in a magnetic chicane that has the identical function of the grating compressors in CPA. The X-ray laser produced by these electrons has been focused to peak intensities of 1020W/cm2, and higher intensities are only limited by the quality of the focusing optics. Since the wavelength is so much shorter than conventional lasers, the science
case and applications are quite different: The applications of these sources are in producing and imaging high energy density matter, ultrafast X-ray diffractive imaging and molecular movies, and ultrafast high-intensity X-ray-matter interactions.
Ultrarelativistic Particle Beams Boost Laser Intensities
With present PW-level lasers, focused intensities have reached the 1022 W/cm2 region, but far higher intensities are available in the rarefied and limited environment of relativistic particle beams. When a laser pulse from a high-intensity laser collides head-on with a relativistic particle, the laser intensity as viewed in the particle rest frame is higher by a factor of 4γ2, where γ is the Lorentz frame relativistic boost. For example, at SLAC the electron energies are in the range of 15 GeV (based on using one-third of the accelerating sections), so the 4γ2 intensity increase factor is more than one billion. This was demonstrated for focused terawatt lasers and 45GeV electron beams in the 1990s, where center of mass intensities greater than 1028 W/cm2 were inferred. With a petawatt laser focused to only 1020 W/cm2, the boosted intensity would exceed the “Schwinger limit,” the intensity required to break down the vacuum, and this novel environment has been suggested as a laboratory for exotic phenomena in particle physics.
In subsequent sections of this report the committee provides more detailed discussions of the technology basis for present PW-class lasers, prospects for future technologies that will lead to higher peak powers as well as higher pulse rates, and status of PW-class laser capabilities specific to the United States.
The highest power lasers, capable of the highest focused intensities, are certainly large and expensive; but the technical limits to power are not simply the cost. Because of CPA, the laser construction expense is only a few percent of the NIF laser, but still measured in the range of $10 million, not counting conventional construction of the facility that houses them or performs experiments with the light.
The current highest-powered lasers that are under construction in Europe and Asia (though not in the United States at present) have peak power of 10 petawatts and have individual costs including conventional construction on the order of $100 million. Their power is limited by several key elements in the optical path: The gain medium, a transparent solid with a rare-earth dopant, must amplify the light used in CPA without distorting it, and the passive optical elements, which consist of lenses, mirrors, dispersive elements and other more specialized devices, must withstand the peak power inside the laser. Figure 1.1 shows a world map with the locations of most of the 0.1 petawatt or higher power lasers. Total expenditures on these facilities are reported to be in the range of $4 billion.1
The laser gain material of choice for most of the lasers under construction now is titanium-doped sapphire, which utilizes CPA and can efficiently convert the excitation by long energetic pulses of lower-powered laser light from more conventional lasers into extremely short and powerful laser pulses at a central wavelength of about 800 nm. Other choices for petawatt-class lasers under current construction or in advanced design include CPA with mixed glass lasers, a nonlinear conversion method called optical parametric CPA, or OPCPA.
X-ray free-electron lasers have different scaling limitations, since they use wholly different technology based on ultrarelativistic electron beams. Current design maxima are in the range of 10 millijoule pulse energies, up to terawatt peak power, below 100 nm focal waists, and below 10 femtosecond pulse durations. When combined, this is a 10 TW laser with a focused intensity of 1022 W/cm2. Engineering advances in superconducting RF accelerator designs, tapered undulators, low emittance photocathodes, seeded laser operation, or focusing mirrors could improve these numbers.
Limits to Scaling and the Path Toward Still More Intense Lasers, Exawatt
The current limits to scaling to higher powers for optical wavelength lasers is damage to optical elements, and elements with the lowest damage thresholds, which
are the real limits to the maximum achievable power, are the special dispersion compensation optics required for CPA or OPCPA. These are typically diffraction gratings. Some future technological advances will be required to continue to scale laser powers to the 1,000 petawatt, or 1exawatt, level, and the current activity in this area is summarized in this report. It is likely that such lasers will approach or exceed the billion-dollar price tags of the high energy fusion lasers such as NIF or the particle accelerators used for X-ray FELs.
Laser-Electron Colliders Scaling Limits
The benefits to combining high-intensity lasers with relativistic particle beams have several paths to scaling since the intensity in the rest frame of the electron scales as γ2. In an earlier configuration designed to create weak vector boson particles, the SLAC accelerator generated 45GeV electrons, or γ = 90,000. If this could be combined with the current best reported intensity from a petawatt laser of I = 1022W/cm2, combined together these two sources could produce an almost unimaginable intensity of 1033W/cm2, one thousand times the Schwinger intensity to spark the vacuum. This provides an opportunity to reach intensities far higher than any current or contemplated future technology.
|AFOSR||Air Force Office of Scientific Research|
|ALLS||Advanced Laser Light Source (Can.)|
|ALPS||Attosecond Light Pulse Source (Eur.)|
|AMO||Atomic, Molecular and Optical|
|APRI||The Advanced Photonics Research Institute (S. Korea)|
|ARC||Advanced Radiographic Capability|
|ARRA||American Recovery and Reinvestment Act|
|ASAP||Academic Strategic Alliance Program|
|ASE||Amplified spontaneous emission|
|AWE||Atomic Weapons Establishment (U.K.)|
|BELLA||Berkeley Lab Laser Accelerator|
|BES||Basic Energy Sciences (DOE)|
|BOC||Balanced optical cross correlator|
|BSM||Beyond the Standard Model|
|CAEP||Chinese Academy of Engineering Physics|
|CALA||Centre for Advanced Laser Applications (Ger.)|
|CALGO||CaAlGdO4, a laser crystal host for Yb|
|CAMOS||Committee on AMO Science (NAS)|
|CDI||Coherent diffractive imaging|
|CEA||Alternative Energies and Atomic Energy Commission (Fr)|
|CERN||Center for European Nuclear Research (Sw)|
|CESTA||Centre d’études scientifiques et techniques d’Aquitaine (Fr.)|
|CETAL||Centrul de Tehnologii Avansate cu Laser (Romania)|
|CILEX||Centre Interdisciplinaire Lumiere Extreme|
|CIRP||The International Academy for Production Engineering|
|CISE||Computer and Information Science and Engineering|
|CLF||Central Laser Facility (U.K.)|
|CLPU||Spanish Pulsed Lasers Centre|
|CLUPS||Laser Center of the University of Paris-South (Fr.)|
|CME||Center of mass energy|
2 M. D. Perry et al., “Petawatt Laser Pulses,” Optics Letters 24, no. 3 (February 1, 1999): 160, doi:10.1364/OL.24.000160.
|CNRS||National Center for Scientific Research (Fr.)|
|CRADA||Cooperative Research and Development Agreement|
|CUOS||Center for Ultrafast Optical Science|
|DARPA||Defense Advanced Research Agency|
|DKDP||Deuterated potassium di-hydrogen phosphate, also called KD*P|
|DLA||Direct Laser Acceleration|
|DOD||Department of Defense|
|DOE||Department of Energy|
|DOT||Department of Transportation|
|DPA||Divided pulse amplification|
|DPSSL||Diode-pumped solid state laser|
|DRACO||Dresden Laser Acceleration Source (Germany)|
|DRC||Dynamic ramp compression|
|EDP||Extraction during pumping|
|EEHG||Echo effect harmonic generation|
|ELBE||Electronic Linac for beams with high Brilliance and low Emmitance|
|ELI||European Laser Infrastructure|
|ERDF||European Regional Development Funds|
|ERIC||European Research Infrastructure Consortium|
|ESFRI||European Strategy Forum for Research Infrastructure|
|FAIR||Facility for Antiproton and Ion Research|
|FAP||Sr5(PO4)3F, a laser crystal host for Yb|
|FEL||Free electron laser|
|FES||Fusion Energy Science|
|FFRDC||Federally Funded Research and Development Center|
|FIREX||Fast ignition realization experiment|
|FOCUS||Frontiers in Optical Coherent and Ultrafast Science|
|FWHM||Full width at half maximum|
|GIST||Gwangju Institute of Science and Technology (S. Korea)|
|GSI||Gesellschaft für Schwerionenforschung|
|HAPLS||High-Repetition-Rate Advanced Petawatt Laser System|
|HED||High energy density|
|HEDP||High energy density physics|
|HEDS||High energy density science|
|HEL||High energy, continuous-wave lasers|
|HEP||High energy physics|
|HGHG||High-gain harmonic generation|
|HHG||High harmonic generation|
|HIL||High intensity laser|
|HPLS||High power laser system|
|HSG||Human salivary gland|
|HZDR||Helmholtz-Zentrum Dresden-Rossendorf Laboratory|
|IAP||Institute of Applied Physics|
|ICAN||International Coherent Amplification Network|
|ICF||Inertial confinement fusion|
|ICFA||International Committee for Future Accelerators|
|ICUIL||International Committee for Ultra-Intense Lasers|
|IEEE||Institute of Electrical and Electronic Engineers|
|ILE||Institute of Laser Engineering (Jap.)|
|INFLPR||National Institute for Laser, Plasma, and Radiation Physics|
|INRS||Institut national de la reserche scientifique (Can.)|
|IZEST||International Zetta-Exawatt Science and Technology|
|JAEA||Japan Atomic Energy Agency|
|JHPSSL||Joint High Power Solid-State Laser|
|JTO||Joint Technology Office|
|KAREN||Kansai Advanced Relativistic Engineering|
|KDP||Potassium di-hydrogen phosphate|
|KD*P||Deuterated potassium di-hydrogen phosphate, also called DKDP|
|KGW||Potassium gadolinium tungstate (KGd(WO4)2)|
|KYW||Potassium yttrium tungstate (KY(WO4)2)|
|LANL||Los Alamos National Lab|
|LASIK||Laser-Assisted In-situ Keratomileusis|
|LBNL||Lawrence Berkeley National Laboratory|
|LCLS||Linac Coherent Light Source|
|LFEX||Laser for Fast Ignition Experiment|
|LHC||Large Hadron Collider|
|LIBRA||Laser Induced Beams of Radiation and Applications|
|LIBS||Laser-induced breakdown spectroscopy|
|LLE||Laboratory for Laser Energetics|
|LLNL||Lawrence Livermore National Laboratory|
|LMJ||Laser Mégajoule (Fr.)|
|LOCSET||Locking of optical coherence by single-detector frequency tagging|
|LSW||Light scattering through a wall|
|LWFA||laser wakefield accelerator|
|MEC||Matter in extreme conditions|
|MFE||magnetic fusion energy|
|MOKE||Magneto-optic Kerr effect|
|MPQ||Max Planck Institute for Quantum Optics|
|MPS||Mathematical and Physical Sciences|
|MRI||Magnetic resonance imaging|
|MURI||Multidisciplinary University Research Initiative|
|NIF||National Ignition Facility|
|NIH||National Institutes of Health|
|NNSA||National Nuclear Security Administration|
|NOPA||Non-collinear optical parametric amplifier|
|NRF||Nuclear resonance fluorescence|
|NSF||National Science Foundation|
|OECD||Organization for Economic Cooperation and Development|
|ONCORAY||Center for Radiation Research in Oncology|
|ONR||Office of Naval Research|
|OPA||Optical Parametric Amplifier|
|OPAL||Optical Parametric Amplifier Line|
|OPCPA||Optical parametric chirped-pulse amplifier|
|OPG||Optical parametric generation|
|OPO||Optical parametric oscillator|
|OSA||The Optical Society|
|OSTP||Office of Science and Technology Policy|
|PAL||Pohang Accelerator Laboratory (S. Kor.)|
|PALS||Prague Asterix Laser System (Eur.)|
|PEARL||PEtawatt pARametric Laser|
|PENELOPE||Petawatt, Energy-Efficient Laser for Optical Plasma Experiments|
|PET||Positron emission tomography|
|PETAL||PETawatt Aquitane Laser|
|PFC||Physics Frontier Center|
|PHELIX||Petawatt High Energy Laser for heavy Ion eXperiments|
|POLARIS||Petawatt Optical Laser Amplifier for Radiation Intensive experimentS|
|PSAAP||Predictive Science Academic Alliance Program|
|PULSE||Photon Ultrafast Laser Science and Engineering|
|QST||Quantum and Radiological Science and Technology|
|RAL||Rutherford Appleton Laboratory|
|RAS||Russian Academy of Science|
|ROI||Return on investment|
|SACLA||Spring-8 Angstrom Compact free electron LAser|
|SASE||Self-Amplified Stimulated Emission|
|SAUUL||Science and Applications of Ultrafast Ultra-intense Lasers|
|SBE||Social, Behavioral, and Economics Sciences|
|SBIR||Small Business Innovation Research|
|SC||Office of Science (DOE)|
|SCAPA||Scottish Centre for the Application of Plasma-based Accelerators|
|SEL||Station of Extreme Light Science|
|SIOM||Institute for Optics and Fine Mechanics (China)|
|SLAC||Stanford Linear Accelerator Center|
|SNL||Sandia National Laboratory|
|SPIE||The International Society for Optics and Photonics|
|SPP||Strategic Partnership Project|
|SPPS||Sub-Picosecond Pulse Source|
|SSAA||Stockpile Stewardship Academic Alliance|
|SSP||Stockpile Stewardship Program|
|STC||Science and Technology Center|
|STFC||Science and Technology Facilities Council (U.K.)|
|STROBE||Science and Technology Center on Real-Time Functional Imaging|
|STTR||Small Business Technology Transfer|
|SULF||Superintense Ultrafast Laser Facility|
|TARANIS||Terawatt Apparatus for Relativistic and Nonlinear Interdisciplinary Science (U.K.)|
|TARPES||Time and angle-resolved photoemission|
|TBD||To be determined|
|TMI||Thermally induced mode instability|
|UFE||Ultra-broadband front end|
|UFL||Russian acronym for their megajoule-class laser|
|USN||United States Navy|
|VSF||Image relay (in vacuum)|
|WDM||Warm dense matter|
|WWII||World War II|
|XCAN||Extreme Coherent Amplification Network (see also ICAN)|
|XCELS||Exawatt Centre for Extreme Light Studies|
|XFEL||X-ray Free Electron Laser|
|YAG||Yttrium Aluminum Garnet|
|YLF||Yttrium lithium fluoride (YLiF4)|