Experimental Studies On Femtosecond Fiber Amplifiers

Ultra-short pulse fiber lasers and amplification systems are widely used in various frontier areas, such as the generation of THz, the research of micro-world and ultrafast process detections. Self-similar parabolic pulses which are generated in a fiber amplifier with normal group-velocity dispersion have become more and more popular because of their attractive characteristics, such as resistance to optical pulses breaking, the typical parabolic shape and the constant linear chirp. All the characteristics of self-similar pulses are only depended on the initial pulse energy and the fiber parameters. In particular, the output optical pulses can be compressed into shorter ones than the input pulses owing to their strict linear chirp.The self-similar pulse theoretical model is introduced in this paper, the impacts on the evolution of self-similar pulses by initial pulse parameters are analyzed and the design standards of a self-similar amplification system are obtained. A femtosecond pulse fiber amplification system is set up to verify that the theory of the amplification system is consistent with the theoretical model through test and analysis.The main work is summarized as follows:1. We introduce the theory and development of ultra-short pulse systems and amplifier systems, after comparing the characteristics of different systems, we focus on the features of self-similar amplification system and point out the advantages of the system.2. Two self-similar pulse theoretical models based on NLSE and G-L equation are described in this paper, The asymptotic solutions of the model are also obtained from the two equations.3. We discuss the application conditions of the asymptotic solutions which are obtained from NLSE and G-L equation, and analyze the influences on the evolution of self-similar pulse by dipole relaxation time, third-order dispersion, initial pulse parameters and gain narrowing effect. At last we obtain the design standards of the amplification system. These design standards are proved to be right by numerical simulations and the analysis of experimental systems in the reference papers.4. A femtosecond fiber amplification system based on the self-similar pulse theoretical model is set up. We analyze the impacts on the output pulse that may generate from many different factors by comparing the results of experiment and theory, the feasibility of self-similar pulse theoretical model and the correctness of design standards are proved through the results of the experiment. Also the group velocity dispersion is compensated by a DCF, and finally we get an output pulse which has 113 fs pulse width and 500 mW power.