Rltraprecision Machinig of Optical Materials for Deep Ultra Violet Lasers of High Brightness and Improvement of Optical Performancs

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Deep Ultra Violet (DUV) lasers of high brightness are expected as a light source for the next generation micro lithography, laser micro processing due to photo-chemical reaction and laser fusion. However, there are serious problems such as the limitation of optical materials to be transmitted, lack of experience of machining on the optical materials in high precision and laser induced damages of the materials. This research work is intended to propose the flat optical components for DUV lasers of high brightness in high precision, high transmittance, high Laser Induced Damage Threshold (LIDT) and high reliability.The (111) surfaces of high purity calcium fluoride (CaF_2) single crystals for DUV were polished and 0.16nm rms in surface roughness was obtained on the float polished surface, measured with an atomic force microscope (AFM). From the observation with a high voltage transmission electron microscope (HVTEM), it was clarified that the float polished surface shows perfect (111) lattice and small atomic steps and there are no damage on the subsurface. We obtained a fourth harmonic laser of 266nm in wavelength by using nonlinear crystals of KDP and CLBO from Nd:YAG lasers. From the irradiation of the laser on the GaF_2 crystals, LIDT was measured. The LIIDT numbers are different among the CaF_2 crystals in various benders, surface finish and laser irradiation number.