Thermal blooming is an atmospheric effect, seen in high energy laser beams. It is the result of the nonlinear interaction of laser radiation with the propagation medium, usually air, which is heated by the absorption of a fraction of the radiation. The amount of energy absorbed is a function of the laser wavelength. The term "thermal blooming" is often used to describe any type of self-induced "thermal distortion" of laser radiation.
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Thermal blooming Wikipedia(Text) CC BY-SA