| High power ytterbium-doped fiber amplifier was found widespread application in scientific research, industry and military areas, due to its high compactness, high efficiency, high signal to noise ratio, good beam quality. In particular, the optical pulse generating system of high energy solid-state laser facility should provide the high-power seed pulse at 1053nm with good beam quality, high signal to noise ratio, and which must satisfy the certain temporal shape, spectral characteristic and polarization characteristic. The output energy, beam quality and signal to noise ratio of the optical pulse generating system were determined by high power ytterbium doped fiber amplifier to a certain degree, and the gain design of amplifier is the key component in the energy distribution of the whole system. However, the ASE noise, nonlinear effect and saturation distortion in the fiber amplifier had badly effect on output ability of the amplifier. Therefore, on the one hand, in order to ensure the output index of the optical pulse generation system, such as energy, spectral width, pulse duration etc, on the other hand, in order to ensure the whole optical pulse generating system to work safely and stabilitily in the longer period, it is very important to design the work point of the amplifier, and figure out the factor which had badly effect on the amplifier such as ASE noise, nonlinear effect and saturation distortion.In this paper, the amplification and transmission characteristics of the high power all fiber ytterbium-doped fiber amplifiers were investigated theoretically and experimentally. The mainly research results include: the theory of the high power ytterbium doped fiber amplifier was built; The ASE noise power characteristic and the saturation amplification characteristic of high power ytterbium fiber amplifier were numerical simulated,the results show that could reduce the ASE noise and avoid the saturation distortion by selecting the gain fiber and designing the gain of the fiber amplifier respectively; The linear transmission characteristics of the fiber amplifier were theoretically studied. The main loss in the amplifier, the damage threshold were analyzed, and the way that could be used to solve the fiber end face damage utilizing the end-cap device was introduced; The nonlinear transmission characteristics of the fiber amplifier were theoretically investigated. The threshold characteristics of SBS and SRS were numerical analyzed, the result show that the threshold of SBS and SRS were improved by selecting the shorter length and larger core diameter gain fiber; In order to avoid the utrashort pulse shape and spectral distortion in the high power ytterbium doped fiber amplifier, self-similar propagation and amplification of the high power ultra-short pulse in the ytterbium-doped large mode fiber were investigated, the results show that when the pulse duration ,energy and gain satisfied the certain relation,the utrashort pulse shape and spectral evolved into the parabolic shape, and the chirp was linear ,so the pulse can be compressed easily, which provided the theoretical basis and the promising way for realizing the all fiber high peak power ultra-short pulse generation system.High power LMA ytterbium-doped fiber amplifier was designed in the experiment based on the theoretical analysis. In the fiber amplifier, many difficult problems such as the coupling of the pump and signal light, the isolation between two stage amplifier, the noise manipulation and saturation amplification suppression were solved, at the same time, the occur of the nonlinear effect and the damage in the gain fiber were controlled by selecting the proper gain fiber in the amplifier. When the input pulse is narrow band and its duration is 5ns, the gain of the amplifier is 17dB, the amplified pulse power is 700W.when the input pulse duration and spectrum width are 2.0ns and 1.2nm respectively, the fiber amplifier reached the saturation state, at the same time the gain of the amplifier is 33dB, the peak power of the amplified pulse reached 19.34kW.Through the theoretical and experimental study of the amplification and transmission characteristics in the high power ytterbium doped fiber amplifier, the coupling problem of the high power pump and signal was resolved, and it is successful to realize the all fiber pulse generation system; the ASE noise problem was solved in the theory and experiment, the system noise was reduced dramatically; the threshold of the gain fiber damage and nonlinear effect were analyzed, which introduced the basis for the designing fiber amplifier to avoid the fiber damage and nonlinear effect; the sample fiber amplifier in the experiment was successfully applied in the power fiber amplifier module of the high power solid-state laser pulse generation system, which realized the high power all fiber optical pulse generation system. |
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