Study On The Propagation Properties Of Chirped Pulse With High Power And Energy

The propagation properties and beam quality of the chirped pulse in the ultrashort pulse system are always the interested problems. During the process of the chirped pulse amplification, the spatial distribution, temporal profile and spectrum distribution of the output pulse are affected by the effects, such as the amplified spontaneous emission (ASE), gain narrowing, gain saturation, self-phase modulation, self-focusing and the dispersion in the gain medium, resulting in the influence on the amplification, compression and beam quality of the pulse. How to decrease or avoid the above effects, as well as increasing the output power and improving the beam quality are the important and difficult research work on the high power ultrashort pulse system. The goal of this thesis is to study the influence of the amplified spontaneous emission on the store energy of the Ti:sapphire and the properties of linear and nonlinear propagation and amplification. The main results obtained in this thesis can be summarized as follows:1. The temporal properties of the amplified spontaneous emission in the gain medium and the influence of ASE on the distribution of store energy were calculated and analyzed by using population equation and 2D ray-tracing, in which the influence of different emission profile on the store energy of the medium was considered. The influence of ASE on the store energy distribution of the gain medium with different thickness was discussed and the methods used to suppress the ASE of the Ti:sapphire amplifier were proposed. Furthermore, thestore energy distribution of the main amplifier of the SILEX-I system was calculated and simulated.2. During the process of the propagation and amplification of the chirped pulse in the gain medium, the effects of the gain narrowing, gain saturation, dispersion, self-phase modulation were simulated and analyzed by using the nonlinear Schrodinger equation. The results have shown that the influence of the dispersion and self-phase modulation on the chirped pulse was slight but distinct to the femtosecond pulse. The distortion of the temporal and spatial profiles was induced by the gain narrowing, gain saturation and ASE, leading to the beam quality worsening.3. Based on the nonlinear Schrodinger equation and population equation, the multi-pass amplification of chirped pulse was studied and the simulation code was built up. The 3TW font end system and 100TW main amplifier of the SILEX-I system were simulated and the results were compared with the experimental results, showing that our code can be used to estimate the amplified capability of the high power ultrashort pulse system.4. The inverse arithmetic of the single pass and multi-pass amplification were proposed and the inverse problem of the chirped pulse with single pass and multi-pass amplification was studied. The inverse simulation and the corresponding experiment were performed for the 3TW system. Furthermore, the profile of the output pulse was calculated by simulating the spectrum of the input pulse shaped by acousto-optic programmable dispersive filter (AOPDF) and compared with the experimental results, showing that the inverse calculation results can provide the valued reference for the AOPDF shaping.5. The spatiotemporal instability theory was introduced and analyzed. The arithmetic of the quasi-discrete Hankel transform (QDHF) was used to split method for solving the nonlinear Schrodinger equation. The error analysis of the QDHF arithmetic was done, showing the feasibility and validity of the arithmetic.6. The self-focusing and small scale self-focusing of chirped pulse were simulated and analyzed by using the nonlinear Schrodinger equation andcalculated results were compared with those of femtosecond pulse. The results have shown that the self-focusing and the small-scale filamentation did not tend to occur for the femtosecond pulse but occurred for the chirped pulse for the same condition. The theory of the long pulse can be used to solve the problem of the chirped pulse self-focusing.The theoretical methods and results in this thesis would be useful for the optimal design of high power ultrashort pulse systems and improving the beam quality of the chirped pulse.