| Fiber Master-Oscillator Power-Amplifier (MOPA) system can further improve the output features of fiber lasers. So it has great academic value and potential for application in industry, space range finding, military and so on.This thesis gives a theoretical and experimental research on Yb-doped double-clad fiber (YDDCF) MOPA system. The main points include:1. The characteristics, application prospect and recent development of fiber MOPA system are introduced.2. The basic principles of YDDCF MOPA system have been summarized, which include the characteristics and key technologies of YDDCF and the basic structure of fiber MOPA system. The principles and theoretical model of active Q-switched fiber laser have also been introduced.3. The signal amplification process of YDDCF MOPA system has been numerically analyzed. The energy conversion of CW (continuous wave) signal amplification is simulated, followed by a discussion of the optimum fiber length. The simulation of pulse signal amplification using finite difference method has also been introduced, and the changes of signal pulse shape caused by amplification have been presented. At last the impacts of amplified spontaneous emission (ASE) on the fiber system are demonstrated.4. The experimental research on pulse pumped YDDCF MOPA system is illustrated.(1) An active Q-switched YDDCF laser is built as the signal source of fiber MOPA system. The signal source can generate 1064nm pulses of 500ns pulse duration at repetition from 100Hz to 50 kHz.(2) A delay circuit is designed to make sure the synchronization of pump pulse and signal.(3) The fiber MOPA system experiment is finished and the effects of repetition and pump pulse duration on output spectrum and pulse duration are studied. Experiment result shows the system has a significant effect on suppressing ASE. When repetition is 400Hz, pump pulse duration 600μs,the MOPA system generates 1064nm pulse laser with average power of 170mW, pulse duration of 538ns and a gain of 10.5dB. |
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