Photo-oxidized Coating on the Optical Materials for High Power Laser Resistance and Waterproof
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Photo-oxidized Coating on the Optical Materials for High Power Laser Resistance and Waterproof Yuji Sato1, Eiichi Matsunaga1, Yoshiaki Okamoto2 and Masataka Murahara1. 1
Innovative Research Initiative, Tokyo Institute of Technology P.O.Box I3-26 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan 2
Okamoto optics co. 8-34 Haramachi, Isogo-ku, Yokohama, Kanagawa, 235-0008 Japan
ABSTRACT A photo-oxidized thin film, which transformed the organic silicone oil into inorganic glass, was coated on optical materials surface by using Xe2 excimer lamp at room temperature. This technique has enabled an optical thin coating capable of transmitting ultraviolet rays [UV] of wavelengths under 200 nm and possessing the characteristics of hardness, strain-free, resistance to high power laser, and resistance to water. UV and IR spectroscopic analysis was carried out for investigation of the oxidized silicone oil. The results revealed that the absorption peak of the CH3 group at 2900 cm-1 decreased as the irradiation time of the excimer lamp increased, and the transmittance of the light in the 172 nm wavelengths conversely became high. The UV transmittance of the silicone oil was 29.2 % before the lamp irradiation; and it improved to 90.6 % after the irradiation for 120 minutes. Moreover, in order to evaluate for resistance to laser damage [J/cm2/10 ns], the films were further irradiated with the Nd: YAG laser of ω [1.06 µm] or 2ω [0.503 µm]. The silica glass substrate had almost same laser tolerance in ω and 2ω, 112 J/cm2 and 113 J/cm2, respectively. The laser damage threshold of the photo-oxidized 100 nm thick film formed on the fused silica substrate was 72 J/cm2 in ω and 107 J/cm2 in 2ω.
INTRODUCTION The fused silica has a low refractive index, a high dielectric constant, and optical transparency in the region of vacuum ultra violet rays [VUV] to near infrared rays [IR]. Therefore, it is used as a protective film for a mirror, lens, and optical crystals. In general, a plasma vapor deposition [PVD] and a chemical vapor deposition [CVD] are widely used to deposit SiO2 thin film onto a substrate heated to around 400℃ by means of vapor deposition, high-frequency ion plating, or sputtering. Mahajan et al. deposited a SiO2 film on the silicon wafer by plasma-enhanced chemical
vapor deposition [PECVD] method using tetra-ethoxy-silane [TEOS] in oxygen atmosphere when maintaining the substrate temperature at 300 degrees centigrade [1]. Dennler et al. also deposited a SiO2 film on the polyimide substrate by PECVD method in the presence of the gases, which consists of 1to 9 mixture of hexamethyl-disiloxane [HMDSO] and O2 gas [2]. On the other hand, Orlowski et al. produced a SiO2 film on the silicon wafer by irradiating a XeCl excimer laser (308 nm) in the oxygen atmospheric pressure when maintaining the substrate temperature at 400 degrees centigrade [3]. Koichi et al. formed the 200 nm and 1000 nm thick SiO2 films on the silicon wafer by laser ablation in the presence of O2 and H2 mixture with the chamber temperatures at 1000 degrees
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