Kj Energy Petawatt Laser Facility Pulse Compression Characteristics Analysis

Laser inertial confinement fusion(ICF) plays a significant role in all fields from scientific research,manufacture application to clean energy sources.Compared with conventional ICF,fast ignition ICF based on ultra-short ultra-intense lasers may obviously reduce the requirement energy of drive laser,scale of facility and cost of project,which has become an intemational research hotspot since the 1990s.The laser driver of the fundamental fast ignition experiment needs to output an ultra-short large-energy laser pulse with duration 1ps～10ps,energy＞1kJ,power＞1PW,temporal S/N＞10⁸,focused intensity 10²⁰W/cm²～10²¹W/cm².Chirped pulse amplification(CPA) is a key technology to reduce nonlinear effects and to improve output energy,which makes it possible to obtain kilo-joule high-energy petawatt lasers.The major idea of this technology is to stretch pulse width before amplification,and then compress pulse width after amplification.Grating compressor is an important component in the kilo-joule high-energy petawatt laser facility,which compress amplified positive chirped pulses to its original durations.Due to the short duration,the large energy,the high temporal S/N and the high focused intensity of the ignition laser pulse,large size high damage threshold gratings should be used,and the grating pair must be placed accurately parallel.Limited by damage threshold,the size of MLD gratings used in the kilo-joule high-energy petawatt laser facility should be meter-size. However,the technology and manufacture level of producing large MLD gratings cannot meet the need of laser drivers used in fast ignitions sufficiently.Although the grating tiling technology,which uses several small size gratings to tile a large size mosaic grating,can reduce the pressure of producing large size gratings,the misalignment detecting,the feedback controlling and the stability keeping of the mosaic grating are rather difficult to be obtained under the recent technology level.And up to the present,no acceptable performances of mosaic gratings used in ultra-short ultra-intense laser systems are reported yet.Besides, compared with traditional CPA laser systems,the large aperture beam,the large size grating, the short pulse duration,the high temporal S/N and the high focused intensity of the kilo-joule high-energy petawatt laser facility lead to much higher adjustment accuracy and stability of the compression gratings.Facing the recent situations,this thesis analyzed the large aperture spectral clipping effects in the kilo-joule high-energy petawatt laser facility which affects temporal and spatial properties of the output pulse,optimized the design of the grating-size-limited compressor, and studied the influences of compression grating adjustment accuracy and stability on the properties of the output pulse when a large aperture laser beam passing a grating-size-limited compressor.The main content can be summarized as follow:1.From the Fourier transform,the theory of chirped pulse stretch and compression is analyzed by deriving the dispersive expressions of a chirped pulse passing a dispersive media. Parallel grating pair can be treated as a strongly dispersive media.Using ray tracing,the wavelength-dependent optical paths between a parallel grating pair is derived.Accordingly, the first-,the second-,and the third-order angle dispersive expressions are obtained.And then, the compression theory of chirped pulses passing a parallel grating pair compressor is studied carefully,which gives a theoretical basis to the design of the compressor in the kilo-joule high-energy petawatt laser facility.2.A spectral clipping model of a large aperture laser beam passing a grating-size-limited compressor is developed.And the influences of the spectral clipping effects of the stretcher,the amplifier,and the compressor in a CPA laser system on the temporal and spatial properties of focal pulses are analyzed theoretically and simulated numerically.When the designed focal pulse is achieved,the minimal bandwidths of the stretcher and the compressor are optimized to reduce the needed size of gratings.3.The influences of compressor parameters on the output pulse energy are analyzed while short duration pulses are outputting.And three basic parameters affecting the design of the grating compressor in the kilo-joule large-energy petawatt laser facility are obtained. Consequently,an optimization of the grating-size-limited compressor to avoid using mosaic gratings and output a maximum-pulse-energy is developed.4.When a grating-size-limited compressor is used to compress a large aperture laser beam,the effects of the compression grating adjustment accuracy on the temporal and spatial properties of the recompressed pulse are investigated.And the influences of 'tilt','tip',and 'rot' of the compression grating on the angle drift,the duration,and the inclination of the output pulse are discussed.Then,to meet the need of fast ignition experiments,a helpful theoretical basis of compression grating adjustment accuracy and stability in the kilo-joule high-energy petawatt laser facility is developed.5.To build the kilo-joule large-energy petawatt laser facility with a 10⁸ focal temporal contrast,the minimal bandwidths of the stretcher and the compressor are simulated;the maximal output pulse energy of the 500mm-grating compressor is explored;and the meter-size compression grating adjustment accuracy and stability are analyzed to reach 10²⁰W/cm² focused intensity.This thesis is part of the research of the kilo-joule high-energy petawatt laser facility, which provides an inchoate design of the pulse compression system and an important reference value to designs and installations of other ultra-short ultra-intense laser systems.