Numerical Study Of Aerosol-induced Thermal Blooming

With the development of laser technology, high-energy laser are playing an increasingly important role in military and civilian fields. When the high-energy laser are propagated in the atmosphere, these can lead to a series of effects which severely limit the effective propagation. Thus, study propagation rules of laser beams through the atmosphere for the effective application of the high-energy laser, is of great significance.Thermal blooming is a very important nonlinear effect. When the high-energy laser propagation in the atmosphere, the molecular and atmospheric aerosol particles will absorb laser energy with heating expansion and density decreased, resulting in decreased local refractive index, which is equivalent to a normally formed in the atmosphere from the negative thermal lens, beam caused by expansion of bending distortion is refracted beam change in a very complex shape. It is the existence of such phenomena, to a certain extent, that hampered the high-energy laser propagation.This paper studies the thermal blooming due to aerosol particles: aerosol particles absorb energy from a high-energy laser beam , heat the air through thermal conduction, form the uneven distribution of air in the beam, and affect the laser wave, finally affect the propagation of high-energy laser.There are three main parts in this thesis:1. The spectral distribution of atmospheric aerosol particles and refractive index are discussed. The effective absorption coefficient of aerosol particles is numerically computed. Through numerical analysis, the impact of factors include laser wavelength, refractive index of aerosol particles, particle aerosol particle size distribution and its heat capacity.2. The paraxial wave equation and density perturbation equation are detailed analyzed from Maxwell's equations and hydrodynamic equations. The laser power threshold of the thermal blooming is computed.3. Numerical algorithm of paraxial wave equation and density of the perturbation equation are detailed discussed. Thermal blooming equations are solved by Discrete Fourier Transformation. On this basis, four factors which impact the thermal blooming due to aerosol particles are also discussed. These factors include laser power, aerosol particles effective absorption coefficient, the horizontal velocity, high-energy laser propagation distance.