Effect of mirror distortion on mode variation of annular-combination CO₂ laser

In the annular-combination CO2 laser with a phase-locking structure, the principle of external-injection phase-locking is analyzed briefly. By using the theory of equivalent strip resonator, the mathematical model to analyze the output mode is established. The effect of different mirror distortions on the output mode of annular cavity is studied. The results show that, in order to obtain light field distributions which is the same as the mode of injection beam, the mirror distortions of M1 and M2 should be controlled at less than 0.07 times of the wavelength. Simultaneously, the effect of mirror distortions on the output mode under the different mirror parameters is studied. The results could help us to optimize the parameters design of this annular-combination resonator.