连续相位板对靶面SBS激光后向传输特性影响研究

激光辐照靶面产生的后向受激布里渊散射(SBS)光经连续相位板(CPP)调制会产生衍射强值并对光学元件造成损伤。利用建立的SBS激光后向近场衍射传输模型及菲涅耳衍射理论,分析并数值模拟了衍射距离、CPP设计参数和应用位置等参量对近场衍射调制的影响。结果表明:在一定范围内,近场调制度随衍射距离的增大而迅速增强;CPP相位幅度、最小空间周期和频谱控制均会影响近场调制,其中相位幅度的影响较大;倍频CPP对近场调制的影响小于基频CPP对近场调制的影响。CPP后向近场衍射传输分析有助于理解相位型光学器件的近场光强分布,对高功率激光系统中光学元件的排布及CPP的优化具有指导意义。

Status and development of high-power laser facilities at the NLHPLP

In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade(SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion(ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.

Wavefront measurement techniques used in high power lasers

The properties of a series of phase measurement techniques,including interferometry,the Hartmann–Shack wavefront sensor,the knife-edge technique,and coherent diffraction imaging,are summarized and their performance in high power laser applications is compared.The advantages,disadvantages,and application ranges of each technique are discussed.

A novel cleanliness control method for disk amplifiers

As the key part for energy amplification of high-power laser systems,disk amplifiers must work in an extremely clean environment.Different from the traditional cleanliness control scheme of active intake and passive exhaust(AIPE),a new method of active exhaust and passive intake(AEPI)is proposed in this paper.Combined with computational fluid dynamics(CFD)technology,through the optimization design of the sizes,shapes,and locations of different outlets and inlets,the turbulence that is unfavorable to cleanliness control is effectively avoided in the disk amplifier cavity during the process of AEPI.Finally,the cleanliness control of the cavity of the disk amplifier can be realized just by once exhaust.Meanwhile,the micro negative pressure environment in the amplifier cavity produced during the exhaust process reduces the requirement for sealing.This method is simple,time saving,gas saving,efficient,and safe.It is also suitable for the cleanliness control of similar amplifiers.

Laboratory study of astrophysical collisionless shock at SG-Ⅱ laser facility

Astrophysical collisionless shocks are amazing phenomena in space and astrophysical plasmas, where supersonic flows generate electromagnetic fields through instabilities and particles can be accelerated to high energy cosmic rays. Until now, understanding these micro-processes is still a challenge despite rich astrophysical observation data have been obtained. Laboratory astrophysics, a new route to study the astrophysics, allows us to investigate them at similar extreme physical conditions in laboratory. Here we will review the recent progress of the collisionless shock experiments performed at SG-Ⅱ laser facility in China. The evolution of the electrostatic shocks and Weibel-type/filamentation instabilities are observed. Inspired by the configurations of the counter-streaming plasma flows, we also carry out a novel plasma collider to generate energetic neutrons relevant to the astrophysical nuclear reactions.

An important effect of filamentation instability on laser fusion physical processes

The process of high power laser interaction with the large scale length corona plasma produced by the leading edge of the laser pulse has been investigated. Early experimental results are re-analyzed and conclusions drawn. In particular,studies of the close connection of unstable filamentation instability with – mainly – two-plasmon decay and – partly –stimulated Raman scattering, stimulated Brillouin scattering, and resonance absorption are carried out in this paper. The positive and negative effects of filamentation instability are also discussed.

Multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array

Lens-less Fourier-transform holography has been actively studied because of its simple optical structure and its single-shot recording.However,a low-contrast interferogram between the reference and object waves limits its signal to noise ratio.Here,multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array is proposed in the experiment and demonstrated effectively to improve the signal to noise ratio.The key technique in our proposed method is a Greek-ladder sieve array,which acts as not only a wave-front modulator but also a beam splitter.With advantages of the common path,single shot,and no need for a lens,this system has enormous potential in imaging and especially in extreme ultraviolet and soft X-ray holography.

Theoretical analysis of frequency modulation-to-amplitude modulation on the final optics and target of the SG Ⅱ-Up laser facility

Frequency modulation(FM)-to-amplitude modulation(AM) conversion is an important factor that affects the time±power curve of inertial confinement fusion(ICF) high-power laser facilities. This conversion can impact uniform compression and increase the risk of damage to optics. However, the dispersive grating used in the smoothing by spectral dispersion technology will introduce a temporal delay and can spatially smooth the target. The combined effect of the dispersive grating and the focusing lens is equivalent to a Gaussian low-pass filter, which is equivalent to 8 GHz bandwidth and can reduce the intensity modulation on the target to below 5% with 0.3 nm @ 3 GHz + 20 GHz spectrum phase modulation. The results play an important role in the testing and evaluating of the FM-to-AM on the final optics and the target, which is beneficial for comprehensively evaluating the load capacity of the facility and isentropic compression experiment for ICF.