Numerical simulation of aero-optical thermal blooming effects on laser propagation through an inner channel

One of the primary challenges in developing higher-power laser systems is the aero-optical thermal blooming effect that occurs during laser beam propagation through the inner channel. This effect refers to the phase distortion and degradation of far-field beam quality due to the uneven changes in temperature and density of the flow field within the channel as the gas medium absorbs the laser's energy. Currently, there is still a lack of high-accuracy and systematic coupling numerical simulation method for the study of the thermal effect. In this study, thermal blooming effect was calculated and analyzed based on the research framework of the coupling of light field and flow field. Differences between the geometric ray tracing method and the linear integration method in calculating the wavefront distortion were compared, which proved that the approximate treatment of beam’s rectilinear propagation can be used to deal with the case discussed. The wavefront distortion was fitted by Zernike polynomial, and the distortion level and its influence on far-field intensity characteristics were analyzed in combination with adaptive optical correction. The results indicated that without adaptive optical correction, significant wavefont distortion developed within 0.5 seconds and increased approximately linearly with time. Matintaining the ratio of pipe radius to beam radius greater than 1.5 can effectively reduce the thermal blooming effect. Adaptive optical correction reduced wavefront distortion by about 70%. The affects of phase modulation from inner-channel wavefront distortion and far-field transmission led to substantial light intensity reduction and spot diffusion over long propagation distances without improvement measures. Adaptive optical correction can signifingntly improve far field beam quality. Therefore, optimization of laser transmission channel geometry and adaptive optics correction are effective approoches to reduce the thermal effect.