Study For Effects Of Steady-State Thermal Blooming On High Energy Lasers Propagation In The Atmosphere

Various kinds of effects included linear or nonlinear can be caused as high-energy lasers propagation in the atmosphere. Among those effects, thermal blooming is the most important nonlinear phenomenon that must be considered. The research on thermal blooming can effectively facilitate the application of high-energy lasers in both military and civilian fields.At the beginning of the paper, current development situation of thermal blooming and its classification were introduced. Based on fundamental electro-magnetic equation, scalar wave equation for paraxial beams was deduced and the isobaric fluid equation was introduced, which is the foundation of numerical algorithms to solve thermal blooming problems. The lowest power threshold of thermal blooming and Bradley-Hermann thermal distortion parameter which is important to thermal blooming was given subsequently. Then, with our main point focused on steady-state thermal blooming, analytical theories of thermal blooming for both collimated and focused Gaussian laser beam in wind and no wind conditions were discussed and calculated. The result shows that thermal blooming would be stronger with the increment of thermal distortion parameter. However, the analytical solutions, whose application is only limited to small thermal distortion parameter, so numerical algorithms have to been adopted for large thermal distortion parameter. Thus, the commonly used numerical algorithms, especially integral algorithm to solve thermal blooming were introduced. Details contain derivation of integral equation for steady-state thermal blooming, Gauss-Legendre numerical integral algorithm and its modified form by iterative method in order to speed up convergence. With this algorithm, steady-state thermal blooming of 10.6, 1.315 and 3.8 um laser was calculated. The result shows that the greater that of the power or distance for a certain other parameters, the stronger that of thermal blooming. However, the increment of aperture or wind velocity can weaken thermal blooming oppositely. Besides, in case of near sea level haze, thermal blooming of 1.315 um is stronger than that of 3.8um cases. Then, the applicable condition of integral algorithm, the interaction of thermal blooming in existence of turbulence, and the ways to suppress thermal blooming were introduced respectively. The research trend of thermal blooming was discussed at the end of the paper. This research work can provide somewhat guidance for the engineering application of high energy lasers.