Study of effects of steady-state thermal blooming on high energy laser propagation in the atmosphere

Based on the integral method, the effects of the steady-state thermal blooming of laser beam propagation in the atmosphere in existence of wind and its influence on light intensity in the far field are studied. The integral equation of the steady-state thermal blooming is deduced for high energy laser propagation in the atmosphere. The Gauss-Legendre numerical integral algorithm is introduced and modified in order to speed up convergence. The results show that the convergence time is decreased almost two time; moreover, the more the thermal distortion, the greater the improvement becomes. Then, the numerical calculation of thermal blooming at 10.6 and 3.8 μm are performed based on the modified method. The results at 10.6 μm are good as we expected. If we consider further the 3.8 μm case, it is indicated that thermal distortion and spread of the laser beam are enlarged when the transmitted laser power or distance is increased for other fixed parameters. However, the spot distortion is in inverse proportional to the aperture size at a certain power and distance. However, the numerical result shows that the aperture should be neither too large nor too small. Both of these cases can reduce the power density and the area of the effective spot on the target. Furthermore, cost is proportional to the aperture size. Hence, the reasonable selection of the aperture is one of the important parameters for a high energy laser system.