Studies On High Power Mechanical Q-switching CO₂Laser

In recent years, CO₂laser and its Q-switching technology have achieved significantprogress. It provides a possibility for high power, high repetition rate and short-pulsed CO₂laser. This laser is recognized as the best drive laser for Laser Produced Plasma ExtremeUltra Violet Light （LPP EUVL） source，which is one of the key technologies fornext-generation lithography. In this thesis, the resonator stability, laser dynamics, and laserperformance of mechanical Q-switching CO₂laser are studied.The stability of optical resonator cavity in mechanical Q-switching CO₂laser wasstudied based on the optical transfer matrix theory at first. The mechanical Q-switching CO₂laser was achieved by locating a rotating chopper at the confocal point of an intracavitytelescope. The calculated results showed that the separation between two focusing lens andthe distance between lens and coupling mirror had great effect on the stability of the opticalresonator cavity. These parameters were optimized to obtain a stable cavity.Then the four-level model was adopted to simulate the output characteristics of amechanical Q-switching CO₂laser and the kinetic parameters was determined by theoreticaland experimental results, and the output characteristics of laser were studied with differentparameters. Simulation results showed that the laser pulse with higher peak power andbetter waveform was obtained by improving the initial inversion particle number as well asreducing the rise time of the Q-switch.At last, the influence of output coupling ratio, discharge current, repetition rate andtransparent duration of Q-switch on the laser performance, including average power, peakpower and pulse trailing, was experimentally studied. The optimum output coupling ratiowas obtained based on the experimental results. The results also showed that the effect ofthe discharge current and the transparent duration of Q-switch were in agreement with thetheoretical results. These studies will be helpful for the following theoretical and experimental researcheson Q-switched CO₂lasers in the future.