Research On Multi-pass Amplification Of Weak Energy Laser Pulse

Pump laser is a key issue in optical parametric chirped pulse amplification technology. In order to develop a pump laser, the high gain amplified technology of weak signal is investigated. A weak pulse of 5ns, 0.2nJ is amplified by multi-pass technology. In the mean time, system gain and pulse distortion in the process of amplification is discussed. The adjustment technology of the optical path is also discussed.At first, the thesis introduced the design of the front-end of a pump laser, analyzed the physical and optical feature of the gain material Nd:YAG, simulated the process of multi-pass amplification based on the model of laser amplification, analyzed the pulse distortion in the process of pulse amplification, advanced the pulse shape of the front-end pump source for realizing flat-top pump laser.Secondly, in order to realized efficient coupling from laser fiber pulse source to solid state amplifier, the optical design of multiple pass amplification is analyzed and the adjustment on optical system, practical principles on adjustment is advanced. Following the provided method, the accurate adjustment of multi-pass amplifier should be realized.In the end, the multi-pass amplification of weak signal is investigated in the way of double-pass, four-pass and six-pass amplification, and realized the laser amplification of signals which pulse width varied from 5ns, 10ns,20ns, 50ns and 100ns, the influence of cooling system and pump energy is analyzed, and relaxation oscillation and parasitic modes was observed in the process of amplification. It is found that in order to realized the pulse amplification without pulse distortion, the amplification system should work in the region of linearity amplification.Signals with different pulse width have different pulse distortion, for example, pulse distortion of 50ns pulse is small. Therefore, in order to realize the amplification on ns-level signal, parasitic mode should be decreased. By adding a pinhole in the light path, pulse distortion is restrained. And better result should be expected by spatial filter and further more methods.Through analyzing the confronted problems and puzzles, we assume that enhancing the power of injecting signal will obtain better experimental result; with limited condition of signal power, regenerative amplification technology should be adopted to realize high gain amplification. However, the principle of regenerative amplification requires input signal to go backward and forward many times inside the cavity, better quality of optical devices, controlling ASE and preventing parasitic modes should be considered.