Wave-front Aberration Analysis Of Three-lens Configuration Slit Spatial Filters

Spatial filtering technology is the key technology to solve the power- limited problem in high power laser systems. The line- focusing slit spatial filtering technology can increase the area of focal spot and decrease the focal length of the lenses which is possible for a slit spatial filter to suppress the pinhole closure and reduce the dimension of the laser system. As the F number is reduced in slit spatial filters, the wave- front aberrations may cause a huge change of light distribution such as splitting, bending and tilting. The change of light distribution will affect the filtering characteristics of the slit spatial filter.The purpose of this thesis is to figure out the influences of wave aberrations in a three- lens configuration slit spatial filter. The relative changes of the peak intensity irradiated on the edge of the two slits and the near- field contrast as well as the near- field modulation were used to analyzed filtering effects as an aberrated laser beam passing through an ideal slit filter and an ideal la ser beam passing through an aberrated slit filter and an aberrated laser beam passing through an aberrated slit filter, respectively. The wave aberrations were expanded with the Zernike polynomials in square area. The simulation result shows that the influences of each primary aberration are connected with their orders: the spherical aberration and the coma have the biggest influences on the slit spatial filter. When the F number is 14 and the coefficient of spherical aberration is over 0.15μ m or the coefficient of coma is over 0.12μ m, the increase of near- field contrast will reach 10%. When the F number is 10 and the coefficient of spherical aberration is over 0.11μ m or the coefficient of coma is over 0.06μ m, the increase of near- field contrast will reach 10%. When the F number is 20 and the coefficient of spherical aberration is over 0.25μ m or the coefficient of coma is over 0.15μ m, the increase of near- field contrast will reach 10%. The results of this thesis may has potential applications in high power laser systems.