A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The past few years have seen remarkable progress in the development of laser-based particle accelerators. The ability to produce ultrabright beams of multi-megaelectronvolt protons routinely has many potential uses from engineering to medicine, but for this potential to be realized substantial improvements in the performances of these devices must be made. Here we show that in the laser-driven accelerator that has been demonstrated experimentally to produce the highest energy protons, scaling laws derived from fluid models and supported by numerical simulations can be used to accurately describe the acceleration of proton beams for a large range of laser and target parameters. This enables us to evaluate the laser parameters needed to produce high-energy and high-quality proton beams of interest for radiography of dense objects or proton therapy of deep-seated tumours.

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Laser-driven proton scaling laws and new paths towards energy increase

Diffraction gratings were discovered during the 18th century, and they are now widely used in spectrometry analysis, with outstanding achievements spanning from the probing of single molecules in biological samples to the analysis of solar systems in astronomy. The fabrication of high-quality diffraction gratings requires precise control of the period at a nanometer scale. The discovery of lasers in the 1960s gave birth to optical beam lithography in the 1970s. This technology revolutionized the fabrication of diffraction gratings by offering highly precise control of the grating period over very large scales. It is surprising to see that a few years after, the unique spectral properties of diffraction gratings revolutionized, in turn, the field of high-energy lasers. We review in this paper the physics of diffraction gratings and detail the interest in them for pulse compression of high-power laser systems.

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Diffraction gratings: from principles to applications in high-intensity lasers

Fast ignition is an alternate concept in inertial confinement fusion, which has the potential for easier ignition and greater energy multiplication. If realized, it could improve the prospects for inertial fusion energy. It poses stimulating challenges in science and technology, and the research is approaching a key stage in which the feasibility of fast ignition will be determined. This review covers the concepts, the state of the science and technology, the near-term prospects, and the challenges and risks involved in demonstrating high-gain fast ignition.

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Status of and prospects for the fast ignition inertial fusion concepta)

Demonstration of high efficiency third harmonic conversion of high power Nd-glass laser radiation

Petawatt solid-state lasers require meter-sized gratings to reach multiple-kilojoule energy levels without laser-induced damage. As an alternative to large single gratings, we demonstrate that smaller, coherently added (tiled) gratings can be used for subpicosecond-pulse compression. A Fourier-transform-limited, 650-fs chirped-pulse-amplified laser pulse is maintained by replacing a single compression grating with a tiled-grating assembly. Grating tiling provides a means to scale the energy and irradiance of short-pulse lasers.

Demonstration of coherent addition of multiple gratings for high-energy chirped-pulse-amplified lasers.

A one-beam prototype of a large twenty-four-beam phosphate-glass laser system has been built and tested. Basic design characteristics include Nd-doped phosphate glass, rod amplifiers up to 90-mm diam, the propagation of a circularly polarized beam, extensive spatial filtering and imaging, and the use of large-aperture Pockels cells. The prototype system has demonstrated focusable power in excess of 750 GW/beam at 50-psec full width at half-maximum (FWHM) pulse duration and has delivered 165 J of focusable energy in a 500-psec (FWHM) pulse. Maximum beam brightness has been measured to be 4 × 1019 W/cm2 · sr at a firing rate of 2 shots/hr. Peak-to-background energy contrast of 108 has been achieved with this system. A detailed description of the system design and performance is presented.

High-power phosphate-glass laser system: design and performance characteristics

Two large-aperture tiled-grating (1.5 m) compressors, each consisting of four sets of tiled-grating assemblies, have been built for the OMEGA EP high-energy petawatt-class laser system. The techniques used for tiling individual tiled-grating assemblies and for optimizing the overall performance of a tiled-grating compressor are described. Both compressors achieved subpicosecond pulse duration without tiling-induced temporal degradation. A ray-tracing model predicted that the static wavefront of the grating tiles dominated focal-spot degradations when submicroradian tiling accuracy is achieved. The tiled-grating compressors delivered a tighter focal spot compared with subaperture grating compressors with single central tiles.

Demonstration of large-aperture tiled-grating compressors for high-energy, petawatt-class, chirped-pulse amplification systems.

Multikilojoule petawatt lasers using chirped-pulse amplification are being constructed worldwide. Several systems have adopted a tiled-grating approach to meet the size requirements for the compression gratings. Grating tiles need to be precisely phased to ensure a transform-limited focal spot when focusing high-energy laser pulses in the target plane. A computer-control test system that uses a Mach-Zehnder interferometer capable of monitoring and correcting drift in the tiled-grating assemblies within the compressor is described. The differential errors due to eight gratings, within a compressor with four grating assemblies, were compensated by adjusting a single grating.

Phase-locked control of tiled-grating assemblies for chirped-pulse-amplified lasers using a Mach-Zehnder interferometer.

A grating-inspection system and a damage-analysis method have been developed to measure in situ laser-induced damage on a 15-m tiled-grating assembly of the OMEGA EP pulse compressor during a 15-ps, 22-kJ energy ramp The beam fluence at which significant damage growth occurred was determined This is the first report on beam fluence versus laser-induced-damage growth of meter-sized multilayer-dielectric-diffraction gratings This result was correlated to the damage-probability measurement conducted on a small grating sample and is consistent with the fluence, corresponding to 100% damage probability

In situ detection and analysis of laser-induced damage on a 1.5-m multilayer-dielectric grating compressor for high-energy, petawatt-class laser systems.

J. Bunkenburg

Papers

Demonstration of coherent addition of multiple gratings for high-energy chirped-pulse-amplified lasers.

High-power phosphate-glass laser system: design and performance characteristics

Demonstration of large-aperture tiled-grating compressors for high-energy, petawatt-class, chirped-pulse amplification systems.

Phase-locked control of tiled-grating assemblies for chirped-pulse-amplified lasers using a Mach-Zehnder interferometer.

In situ detection and analysis of laser-induced damage on a 1.5-m multilayer-dielectric grating compressor for high-energy, petawatt-class laser systems.