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[en] The output pulse energy from a single-aperture high-energy laser amplifier (e.g. fusion lasers such as NIF and LMJ) are critically limited by a number of factors including optical damage, which places an upper bound on the operating fluence; parasitic gain, which limits together with manufacturing costs the maximum aperture size to ∼ 40-cm; and non-linear phase effects which limits the peak intensity. For 20-ns narrow band pulses down to transform-limited sub-picosecond pulses, these limiters combine to yield 10-kJ to 1-kJ maximum pulse energies with up to petawatt peak power. For example, the Advanced Radiographic Capability (ARC) project at NIF is designed to provide kilo-Joule pulses from 0.75-ps to 50-ps, with peak focused intensity above 1019 W/cm2. Using such a high-energy petawatt (HEPW) beamline as a modular unit, they discuss large-scale architectures for coherently combining multiple HEPW pulses from independent apertures, called CAPE (Coherent Addition of Pulses for Energy), to significantly increase the peak achievable focused intensity. Importantly, the maximum intensity achievable with CAPE increases non-linearly. Clearly, the total integrated energy grows linearly with the number of apertures N used. However, as CAPE combines beams in the focal plane by increasing the angular convergence to focus (i.e. the f-number decreases), the foal spot diameter scales inversely with N. Hence the peak intensity scales as N2. Using design estimates for the focal spot size and output pulse energy (limited by damage fluence on the final compressor gratings) versus compressed pulse duration in the ARC system, Figure 2 shows the scaled focal spot intensity and total energy for various CAPE configurations from 1,2,4, ..., up to 192 total beams. They see from the fixture that the peak intensity for event modest 8 to 16 beam combinations reaches the 1021 to 1022 W/cm2 regime. With greater number of apertures, or with improvements to the focusability of the individual beams, the maximum peak intensity can be increased further to ∼ 1024 W/cm2. Lastly, an important feature of the CAPE architecture is the ability to coherently combine beams to produce complex spatio-temporal intensity distributions for laser-based accelerators (e.g. all-optical electron injection and acceleration) and high energy density science applications such as fast ignition
[en] Inertially confined, ignited thermonuclear D-T plasmas will produce intense blackbody radiation at temperatures T > or approx. 20 keV; it is shown that the injection of GeV electrons into the burning core can efficiently generate high-energy Compton scattering photons. Moreover, the spectrum scattered in a small solid angle can be remarkably monochromatic, due to kinematic pileup; a peak brightness in excess of 1030 photons/(mm2 mrad2 s 0.1% bandwidth) is predicted. These results are discussed within the context of the Schwinger field and the Sunyaev-Zel'dovich effect
[en] The development of microsatellites requires the development of engines to modify their orbit. It is natural to use solar energy to drive such engines. For an unlimited energy source the optimal thruster must use a minimal amount of expendable material to minimize launch costs. This requires the ejected material to have the maximal velocity and, hence, the ejected atoms must be as light as possible and be ejected by as high an energy density source as possible. Such a propulsion can be induced by pulses from an ultra-short laser. The ultra-short laser provides the high-energy concentration and high-ejected velocity. We suggest a microthruster system comprised of an inflatable solar concentrator, a solar panel, and a diode-pumped fiber laser. We will describe the system design and give weight estimates.
[en] Inertially confined, ignited thermonuclear deuterium-tritium plasmas will produce intense blackbody radiation at temperatures of T(greater-or-similar sign)20 keV; it is shown that the injection of GeV electrons into the burning core can efficiently generate high-energy Compton scattering photons, as the high blackbody photon density alleviates the small interaction cross section. Moreover, it is shown that the spectrum scattered in a small solid angle can be remarkably monochromatic, due to kinematic pileup; peak brightness in excess of 1030 photons/(mm2 mrad2 s 0.1% bandwidth) are predicted. These results are also discussed within the context of the Schwinger field and the Sunyaev-Zel'dovich effect
[en] Nonlinear effects are known to occur in light sources when the wiggler parameter, or normalized 4-potential, A=e√(-AμAμ)/m0c, approaches unity. In this paper, it is shown that nonlinear spectral features can appear at arbitrarily low values of A if the fractional bandwidth of the undulator, Δφ-1, is sufficiently small and satisfies the condition A2Δφ∼1. Consequences for the spectral brightness of Compton scattering light sources are outlined. Compton and Thomson scattering theories are compared with the Klein-Nishina cross-section formula to highlight differences in the case of narrow band gamma-ray operation. A weakly nonlinear Compton scattering theory is developed in one (plane wave) and three (local plane wave approximation) dimensions. Analytical models are presented and benchmarked against numerical calculations solving the Lorentz force equation with a fourth-order Runge-Kutta algorithm. Finally, narrow band gamma-ray spectra are calculated for realistic laser and electron beams.
[en] We present the design for a high-speed adaptive optics system that will be used to achieve the necessary laser pointing and beam-quality performance for initial fast-ignition coupling experiments. This design makes use of a 32x32 pixellated MEMS device as the adaptive optic and a two-channel interferometer as the wave-front sensor. We present results from a system testbed that demonstrates improvement of the Strehl ratio from 0.09 to 0.61 and stabilization of beam pointing from ∼75μrad to <2μrad.
[en] Compton scattering of intense laser pulses with ultrarelativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described
[en] Thomson-Scattering based systems offer a path to high-brightness high-energy (> 1 MeV) x-ray and γ-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to optimize such a device, dubbed the ''Thomson-Radiated Extreme X-Ray'' (T-REX) source, targeting up to 680 keV photon energy. Such a system requires precise design of the interaction between a high-intensity laser pulse and a high-brightness electron beam. Presented here are the optimal design parameters for such an interaction, including factors such as the collision angle, focal spot size, optimal bunch charge, and laser energy. These parameters were chosen based on extensive modeling using PARMELA and in-house, well-benchmarked scattering simulation codes
[en] A new class of tunable, monochromatic γ-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photoscience and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. A prototype, capable of producing > 108 0.7 MeV photons in a single shot, with a fractional bandwidth of 1%, and a repetition rate of 10 Hz, is currently under construction at LLNL; this system will be used to perform nuclear resonance fluorescence experiments. A new symmetrized S-band rf gun, using a Mg photocathode, will produce up to 1 nC of charge in an 8 ps bunch, with a normalized emittance modeled at 0.8 mm.mrad; electrons are subsequently accelerated up to 120 MeV to interact with a 500 mJ, 10 ps, 355 nm laser pulse and generate γ-rays. The laser front end is a fiber-based system, using corrugated-fiber Bragg gratings for stretching, and drives both the frequency-quadrupled photocathode illumination laser and the Nd:YAG interaction laser. Two new technologies are used in the laser: a hyper-Michelson temporal pulse stacker capable of producing 8 ps square UV pulses, and a hyper-dispersion compressor for the interaction laser. Other key technologies, basic scaling laws, and recent experimental results will also be presented, along with an overview of future research and development directions
[en] The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has been specifically designed for advanced rf gun applications, with a special emphasis on the production of high-brightness electron beams for free-electron lasers and Compton scattering light sources. The laser pulse can be shaped to a flat-top in both space and time with a duration of 10 ps at full width of half-maximum (FWHM) and rise and fall times under 1 ps. The expected pulse energy is 50 (micro)J at 261.75 nm and the spot size diameter of the beam at the photocathode is 2 mm. A fiber oscillator and amplifier system generates a chirped pump pulse at 1047 nm; stretching is achieved in a chirped fiber Bragg grating. A single multi-layer dielectric grating based compressor recompresses the input pulse to 250 fs FWHM and a two stage harmonic converter frequency quadruples the beam. Temporal shaping is achieved with a Michelson-based ultrafast pulse stacking device with nearly 100% throughput. Spatial shaping is achieved by truncating the beam at the 20% energy level with an iris and relay-imaging the resulting beam profile onto the photocathode. The integration of the system, as well as preliminary laser measurements will be presented