Investigation On A 100-J Laser System And High-Energy And High-Power Stimulated Brillouin Scattering Phase Conjugation

As an important tool for improving the performance of high-energy and high-power laser systems, Stimulated Brillouin scattering (SBS) technique has a broad prospect as practical application. In double-pass and multi-pass laser amplifiers, SBS phase conjugator is used to compensate for both dynamic and static phase errors, and improve the performance of the laser system. In previous study, however, low power intensity was inputted into SBS phase conjugation mirror, that did not conform to the requirement for the high-energy and high-power laser system. In the dissertation, characteristics of the phase conjugation mirror based on SBS with high-energy and high-power are systematically studied, with its application in the high-energy and high-power laser system designed.The thesis is divided into three parts. The first one is the design and performance of hundreds joule level high-energy and high-power laser system. The second part is theoretical and experimental investigations on the characteristics of the high-energy and high-power phase conjugation mirror, while the third part is the design of the SBS phase conjugation mirror.A high-energy and high-power Nd-doped phosphate glass laser system with 100J energy output was designed for the SBS phase conjugation experiment, and the numerical method to simulate the gain of this solid-state laser system was discussed, with the performances of this system at a short-pulse regime and a long-pulse regime investigated. At a short-pulse regime, energies of over 10J were obtained, while a long-pulse regime, the effect of saturation fluence was found and the energies stored in the laser amplifiers were efficiently extracted. The stability at output energies of over 100J was 6%, and the design was optimized by image relaying to produce uniform illumination of near-field distributions.The study on the characteristic of high power intensity SBS phase conjugation is divided into two parts, the theory and the experiment. In the first part, based on the coupled wave equations concerning interaction among the pump field, the Stokes field and the acoustic field in the SBS process, theoretical model of SBS is constructed. Using a scheme with an implicit finite differencing in time and a down-wind differencing in space, the differencing form of the coupled wave equations is established. Under high-energy and high-power laser pumping, the characteristics of both the single-cell and the double-cell SBS phase conjugation mirror are investigated, they are energy reflectivity, phase conjugation fidelity, and the pulse profile. After find the relationship between the characteristics and the parameters including structure parameters and medium parameters, it can be used help design the SBS phase conjugation mirror. In the second part, the characteristics of single-cell and double-cell were studied experimentally.The structure of SBS phase conjugation mirror with high-energy and high-power input is much more complex than that with low power intensity input. According to the theoretical and experimental investigations, the precept for the design of SBS phase conjugation mirror is proposed, including the geometrical structure design, SBS cell design and the rule for medium choice. To meet the requirement of high power intensity SBS phase conjugation mirror, a phase conjugation mirror for double-pass laser amplifier is designed, which is more efficient comparing to traditional absolute two cells amplifier, and it compresses the width of the pulse at the same time. Furthermore, the rules for the SBS phase conjugation mirror with high-energy and high-power are defined, which are applicable for the ordinary SBS phase conjugation mirror too.