Research Of Pulse Green Laser Operating At Variable Repetition Rate

High stable Q-switched solid-state green lasers still play an important role in high-precision micro-processing systems and widely apply in laser materials processing such as solar film etching, glass engraving, wafer scribing, etc. Each of these applications demands high levels of stability, such as pulse energy, pulse width and peak power. At present, commercially available Intracavity frequency doubling Q-switched Nd:YAG lasers have realized stable long-term operation at a fixed repetition rate. Less work concerning the stability of pulse operating at variable repetition rate has been performed. This point is an important content of this dissertation.In this thesis, the reasons which causing fluctuation of green laser pulse are analyzed and discussed in deeply. Some optimal design projects are put forward to achieve optimum harmonic pulse characteristics and stable long-term operation at variable repetition rate. The main research works can be summarized as follows.(1) According to solve the rate equations that describing side-pumped actively Q-switched intracavity frequency doubling Nd:YAG laser, we investigated the influence of pumping rate, resonator loss, repetition rate, phase matching condition, the length of nonlinear crystal on the stability of green pulse. So higher pumping power density, lower resonator loss, accurate phase matching condition and optium length of nonlinear crystal are necessary to realize stable operation of green laser.(2) The novel technique about polarization control and compensation of fundamental wave with wave plate is mentioned and analyzed to decrease the influence of laser crystal's thermal effect such as thermal focal length, thermal stress birefringence and improve the polarization of fundamental wave. Based on the technique, a novel resonator for compensating thermally induced birefringence and self-selecting mode is designed to improve the stability of green laser. At the same time, the conversaion efficency of harmonic wave increases nearly 20%.(3) The influence of the KTP's temperature distribution on the frequency doubling efficiency, resonator stability and intensity distribution of harmonic pulse and stability of harmonic pulse was analyzed. The optimal nonlinear crystal length was obtained to decrease fluctuation of laser pulse caused by variable temperature of KTP crystal. On the other hand, a high precision temperature controller unit with phase change material which has±0.01 degree control accuracy was manufacture to keep the KTP crystal operating at phase matching temperature.(4) Based on the theoretical analysis, optimal design and experiments research, a high stable Q-switched-solid-state green laser is developed. The pulse instability is less than 1% at variable repetition rate (change range: 0~3kHz). The parameters have reached the current level of international commercial green laser. Up to now the green laser has been used in large-scale glass engraving system.