Thermal blooming effect of Hermite-Gaussian beams propagating through the atmosphere.

The thermal blooming effect of Hermite-Gaussian (H-G) beams propagating through the atmosphere is studied analytically and numerically. The analytical expression for the distortion parameter of steady-state thermal blooming of H-G beams propagating through the atmosphere is derived. It is shown that, under the same beam power, the higher the mode order of H-G beams, the weaker the thermal blooming effect. In particular, the thermal blooming effect for a H-G beam is weaker than that for a Gaussian beam. It is found that as the mode order increases, the beam width at the target may decrease due to the thermal blooming effect, although the initial beam width increases. When the cross-wind velocity is large enough, the symmetry of an asymmetric H-G beam may be improved by thermal blooming if the astigmatism parameter is adopted to characterize the symmetry of H-G beams. As the mode order of H-G beams increases, the shift of the beam centroid position decreases, but it takes more time to reach steady-state thermal blooming. On the other hand, the thermal blooming effect on the multimode beam quality is also examined in this paper. It is shown that a minimum beam spot on the target can be obtained if the optimal weighting factor of multimode beams is adopted.