Research On Light Field Modulationof Inclusion In Fused Silica

Large-scale laser driven systems have been developing rapidly in many countries after the idea of laser inertial confinement fusion was presented and confirmed theoretically and technically. However, the anti-damage ability of the optical components has restricted the development of high-power laser systems, because the surface and internal defects can induce damage of the components. Fused silica optical material is one of the most commonly material for the optical elements, and the impurities in the element are usually inevitable during the process of material smelting and element machining. There are two ways that the impurities reduce threshold of optical components, one is the thermal effects, and the other is the modulation effect of the impurities on the incident field. Thermal effects of the impurities have been researched deeply, but reports about the modulation effects of impurities can hardly be found and it is lacking in a quantitative research. The modulation field of a spherical impurity is theoretically modeled and computational analyzed in the paper. The main contents and results are as follows:Based on Mie scattering theory, a model of modulation on incident beam by spherical inclusions in fused silica illuminated by a laser beam was developed. The effects of impurity parameters(size, refractive index) and laser parameters(wavelength, plane wave, Gaussian beam) on the modulated light field were simulated and analyzed. For the case of a plane wave incident with wavelength 355 nm, the results show that modulation effect of inclusions can be ignored when the radius of the particle is smaller than ?/ 10; When the radius of the particle is larger than ?/ 10, for a non-dissipative particle, LIEF(light intensity enhancement factor) increases with increasing radius and decreases with increasing refractive index, and LIEF can reach to the order of 102 in some situations. The backward scattering intensity is much stronger than the forward scattering intensity when the refractive index is less than that of fused silica. For a dissipative particle, the larger the imaginary part of the refractive index, the less LIEF is affected by the real part of the refrac tive index. When the radius increases, forward scattering intensity increases at first and then decline. When the radius is larger than ?/ 2, backward scattering intensity is greater than forward scattering intensity. The position of the highest intensity has a complex relationship with both the size and the reflective index of the impurity. The case of a Gaussian beam incidence is very similar to that of the plane wave incidence except that the width of the Gaussian is smaller than 10 times of the wavelength.In short, impurities behave as micro lens embedded in fused silica, it has a great influence on the damage of optical components caused by local field enhancement. The results have certain significance to dealing with fused silica in the practical application. It can improve the anti-damage ability and service time of optical components to reduce content of particles, especially large-size particles, during the production process of the elements.