Advanced an online low 1ω drive irradiance tuning technique of frequency conversion crystals of high power solid-state laser facility, which can acquire the best match angle of frequency conversion crystals through online low 1ω drive irradiance tuning curve test, and achieve fast and high precision angle correction to assure the frequency conversion crystals to achieve the highest energy conversion efficiency in shot experiments. Analyzed the possibility of online low 1ω drive irradiance tuning technique of frequency conversion crystals, researched the technical scheme of online low 1ω drive irradiance tuning of frequency conversion crystals, and applied this technique on SG facility, which achieved 60%~70% frequency conversion efficiency in high energy shots.
The high power solid laser system is becoming larger and higher energy that requires the beam automatic alignment faster and higher precision to ensure safety running of laser system and increase the shooting success rate. This paper take SGIII laser facility for instance, introduce the basic principle of automatic alignment of large laser system. The automatic alignment based on digital image processing technology which use the imaging of seven-classes spatial filter pinholes for feedback to working. Practical application indicates that automatic alignment system of cavity mirror in SGIII facility can finish the work in 210 seconds of four bundles and will not exceed 270 seconds of all six bundles. The alignment precision promoted to 2.5% aperture from 8% aperture. The automatic alignment makes it possible for fast and safety running of lager laser system.
To assure that the frequency conversion crystals of SG facility are always being in the
best shot position, and have the highest energy conversion efficiency with various beam conducting
directions, we researched the precise tuning technique of frequency conversion crystals with the SG
facility. The on-line quick tuning method of target point detecting with preshot was used in precise
tuning of crystal match angle, and helped to correct the off-line match angle satisfactorily. With
crystal alignment technique and crystal accompany technique, the precise tuning of crystal match
angle can assure the crystals to maintain a stable high efficiency in a long experiment period.
Beam alignment of multi-pass amplification is based on cavity mirror alignment. To optimize multi-segmental parallel cavity mirror alignment arithmetic of high power solid-state lasers, propose a new type of arithmetic of multi-pass beam path cavity mirror based on diffraction symmetry, and the accuracy of multi-pass amplification beam path alignment is improved by 10μrad up to 3.96μrad. The arithmetic avoids low accuracy of CM alignment caused by poor image quality, It makes SG-Ⅲ facility operate long term and properly.
Precise physical experiments place strict requirements on target illumination uniformity in Inertial Confinement Fusion. To obtain a smoother focal spot and suppress transverse SBS in large aperture optics, Multi-FM smoothing by spectral dispersion (SSD) was studied combined with continuous phase plate (CPP) and polarization smoothing (PS). New ways of PS are being developed to improve the laser irradiation uniformity and solve LPI problems in indirect-drive laser fusion. The near field and far field properties of beams using polarization smoothing were studied and compared, including birefringent wedge and polarization control array. As more parameters can be manipulated in a combined beam smoothing scheme, quad beam smoothing was also studies. Simulation results indicate through adjusting dispersion directions of one-dimensional (1-D) SSD beams in a quad, two-dimensional SSD can be obtained. Experiments have been done on SG-III laser facility using CPP and Multi-FM SSD. The research provides some theoretical and experimental basis for the application of CPP, SSD and PS on high-power laser facilities.
Experiment of entire beam wavefront compensation was carried out in a beamline of a high power laser facility, and two adaptive optics systems with different intentions were applied in the chosen beamline. After correction, the far-filed irradiance distribution is concentrated evidently and the entrance rate of 3ω focal spot to a 500-μm hole is improved to be about 95% under number kilojoules energy.
Multi-FM SSD and CPP was experimentally studied in high fluence and will be equipped on all the beams of SG-III laser facility. The output spectrum of the cascade phase modulators are stable and the residual amplitude modulation is small. FM-to-AM effect caused by free-space propagation after using smoothing by spectral dispersion is theoretically analyzed. Results indicate inserting a dispersion grating in places with larger beam aperture could alleviate the FM-to- AM effect, suggesting minimizing free-space propagation and adopting image relay. Experiments taken on SG-III laser facility indicate when the number of color cycles (Nc) adopts 1, imposing of SSD with 3.3 times diffraction limit (TDL) did not lead to pinhole closure in the spatial filters of the preamplifier and main amplifier with 30-TDL pinhole size. The nonuniformity of the focal spot using Multi-FM SSD and CPP drops to 0.26, comparing to 0.84 only using CPP. The experiments solve some key technical problems using SSD and CPP on SG-III laser facility, and provide a flexible platform for laser-plasma interaction experiments. Combined beam smoothing and polarization smoothing are also analyzed. Simulation results indicate through adjusting dispersion directions of one-dimensional SSD beams in a quad, two-dimensional SSD could be obtained. The near field and far field properties of beams using polarization smoothing were also studied, including birefringent wedge and polarization control plate (PCP). By using PCP, cylindrical vector beams could be obtained. New solutions will be provided to solve the LPI problem encountered in indirect drive laser fusion.