Techniques Of Spatial Intensity And Wavefront Control In The High Power Solid-state Laser System

High-power laser plays an important role in national defence, astronomical research and the discovery of new e nergy resources. Large-aperture high-power solid- state laser systems have been set up across the world, such as N ational Ignit ion Facility(N IF) in the USA, O MEGA EP Laser Facility in University of Rochester, and SG- III Laser Facility in C hina. In order to study the scientific problems during the construction of the large- scale laser systems, middle-scale solid-state laser systems have been founded gradually, mainly aimed at completing the verification of physical experiments. A middle- scale solid- state laser system has a similar fluence with the large systems, and they can work with higher efficiency and flexibility. Thus, the construction of a high-performance middle-scale solid- state high- power laser system with high beam quality can really boost the deve lopment of high-power laser systems.In this dissertation, the solid-state laser system is designed with 100 J output energy, which is exactly the middle-scale laser system that can be used to verify the physical phenomemon for large-scale laser systems and conduct experiments of laser induced damage tests for ultraviolet optical elements. The laser system is sophisticatedly built with a master oscillator power amplifier(MOPA) structure. The laser pulse is generated in the front-end with all- fiber optic scheme with 10 n J and nanosecond duration at 1053 nm wavelength. Then the pulse enters into the preamplifier and the main amplifier system which consists of four Nd:glass rod amplifiers pumped by flash lamps with the output energy of about 100 J and the beam size of Φ60 mm. After the frequency converter with 2 KDP crystals, the 351 nm laser generates with energy of about 50 J. The output laser has high beam quality with the capability of spatial beam shaping, wavefront shaping and time- domain pulse shaping with high energy stability and beam point ing stability. The laser operates at a rate of 2 shots per hour, and the near field, energy and waveform of both 1ω and 3ω of each pulse can be measured. The laser system can operate at 1ω/80 J and 3ω/40 J with a long-term stability, which can afford a name as steely weapons- grade “user device”. In this dissertation, the laser system is introduced. The near- field spatial distribution and wavefront distribution of the laser output beam quality are controlled by a SLM and a small-aperture DM, and the output beam quality is effectively improved.First and foremost, the configuration of the solid-state laser system is designed. It uses 4-stage Nd:glass rob two-pass amplification structure and the designed final output is 1053 nm/Φ60 mm/100 J/3 ns. The article introduces five subsystems of the laser setup: all- fiber front- end system, the laser amplification, transportation and energy system, frequency conversion system, parameter diagnostic and controller unit, measurement and synchronization system and computer control system. We design the optical path arrangement of the two-sided vertical truss of the main optical path, and complete the overall optical adjustment. The laser structure design and the installation of the entire laser is introduced as well.Secondly, in order to improve near- field beam quality of the laser output, a programmable liquid crystal SLM is adopted. For 1ω laser, considering the gain in the main amplifiers and the spatial nonuniformity through the trans mit, we take advantage of the liner amplification model to study near- fie ld compensation algorithm. In addition, taking the nonlinear effect generated during the crystal frequency conversion, we make use o f nonlinear transmission model to study the near- fie ld compensation algorithm for 3ω laser. Experiments results show the improvement of the near- fie ld beam quality of both the 1ω and 3ω laser. Meanwhile iteration compensation method is used to overcome the limitation of the single compensation process. It can be demonstrated that high-quality near- fie ld laser output can be obtained through the optimization algorithm on the basis of near- field compensation by using an SLM. After compensation, the near- field modulation of the output 1ω laser is 1.26:1, and the near- field modulation of the output 3ω laser is 1.42:1.Furthermore, a preliminary exploration is made to optimize the wavefront distributions of the laser output. With the analys is of the wavefront measurement method, we determine to use small- aperture DM in the front stage to improve laser wavefront of the system. After the research as well as the experimental verification on the wavefront shaping method of the laser system, we can get quasi- flattop wavefront distribution on the hundred-Joule- level solid-state laser system. Results show that taking advantage of the front-stage small-aperture DM can compensate wavefront aberrations caused within the complex high- power solid- state laser system and improve the final output wavefront. Finally, the PV value of the 1ω laser output wavefront is 0.29 λ and the RMS value is 0.06 λ.Finally, the relationship is studied between the spatial beam shaping using SLM and wavefront shaping using DM in the high power laser system. The scheme of simultaneous compensation of the near- field and wavefront is designed and realized. Results show that the 1ω laser output wavefront PV value is less than 0.4 λ and the near-field modulation is less than 1.4:1.