Waterproof coating on nonlinear optical crystal surfaces by photo-oxidation of silicone oil

摘要

In general, nonlinear-optical crystals are used as a wavelength conversion element for laser. The crystals are, however, deliquescent and absorb moisture in air, which causes clouding. They need to be heated in the oven for humidity control. The development of a protective film, which is moistureproof and transmits UV rays, is expected. We have, therefore, developed a waterproof and hard protective coating on a KH_2PO_4 (KDP) surface at room temperature by photo-oxidation of silicone oil using a Xe_2 excimer lamp. A test of waterproofing was conducted for the treated and untreated KDP crystals. The results showed that the untreated crystal completely dissolved in water thirty minutes after immersing, whereas the coated KDP crystal has neither dissolved nor clouded for three months since immersing in water.