The Study Of Pumping Uniformity In Thin Disk Lasers

Pumping uniformity is a key technology for thin disk lasers to reduce the thermal distortion of laser crystal, achieve high beam quality, high laser power and high optical effiency, as well as the design difficulty of thin diak lasers. This thesis contrapose the multi-pass pumping scheme based on conjugated double parabolic mirrors, by researching the uniformity of pumping source, single focused spot and multi spot overlap, the design of multi-pass pumping scheme is completed with the system misadjustment into account, the optimal scheme is presented and relevant experiment research is carried out. The detail contents are:Firstly, for the uniformity of pumping source, four homogenization methods of microlens array, cylindrical lens, polygon homogenization rod and square fiber are analyzed combining the optical structure, and the square fiber is choosed as the optimal one.Secondly, contraposing the uniformity of single focused spot, the dispersion size of edge image point should be lower than 150?m by researching the imaging property of parabolic mirror.Thirdly, as for the center superposition of multi focused spots, the excellent multi-pass pumping stability of conjugated double parabolic mirrors is verified by analyzing the affects of the optical properties and mismatch of parabolic mirrors and defocus of disk crystal, which ensure the overlap of each focused spot.Fourthly, for the edge overlap of multi focused spots, the affects on the distortion of focused spots caused by the inclination of disk crystal and imaging property of parabolic mirrors have been analysed. The basic reason of distortion is the different magnification on the off-axis direction and its orthogonal directions led by the off-axis collimated beam. Two methods to correct the distortion are raised and achieve good correction results, which are confocal piecewise parabolic mirrors and one-dimensional beam expander system.Fifthly, a new multi-pass pumping scheme of conjugated double parabolic mirrors is presented with right-angle prisms. The key indicators in the system obtain the global optimum, and two multi-pass pumping systems achieve good performances, which are 93.8% and 96.31% in pumping uniformity,4.3kW/cm2 and 5.48kW/cm2 in pumping density, 20 and 48 passes in pumping number respectively.Sixthly, every research link of pump uniformity is verified by experiments, and the overlay pumping spot on the disk crystal appears very homogeneous finally. The operation experiments of CW disk laser based on the two sets of multi-pass pumping systems are carried out. One system has achieved high beam quality laser of M2?1.3, with the output power of 125W and the optical efficiency of 34.2%; the other one has achieved 654W in output power,47.2% in optical efficiency and M2?7.2 in beam quality.