The Big Incentive Area Mode Field Control Of The Laser Resonator And Beam Quality Improvement Study

COILs have been developed to be an attractive chemical laser characterized with high efficiency, high power and short wavelength during the last two decades. But because the flowing of the laser gain media at an supersonic creates the non-uniformity of the gain along the gas flowing direction, it is very difficult to obtain the beams with the quality near to the diffraction limit by using the traditional positive confocal unstable resonator. The main reason is that this resonator is sensitive to the media uniformity and mirrors misaligned. Therefore, an important problem to be resolved is how to reform the resonator structure to produce the light beams with high power and high quality.In this thesis, by considering the above characteristics of the supersonic COIL and the practical demands of output power levels, several novel resonators, including annular output 90° beam rotation ring unstable resonator (AOUR90), unifying phase coupler unstable resonator (UPCUR) and phase step unstable resonator (PSUR) are proposed, while a novel couple approach is also proposed to combine the coherent output beams of multi lasers stably. The main contents and results are listed as follows.1. The annular output 90° beam rotation ring unstable resonator is proposed for the first time, which is suitable for the COIL with the high-power of over 10KW-level. The diffraction integral equation and the formula of equivalent Fresnel number N_eq of this resonator are derived by using matrix method. And it is found by using the fast Fourier Transform (FFT) method that the effects of the tilt mirror, astigmatism and non-uniform gains of the media on the near field and intensity, phase and far field intensity distribution of the AOUR90 and traditional ring unstable resonator. Compared to the traditional ring unstable resonator, the AOUR90 is of several advantages such as the lower misaligned sensitivity, weak requirement for the fabrication accuracy of optical elements, and the strong ability to unify the gains of the media.