| 摘要 |
PURPOSE:To prevent an increase of a loss of light on a reflecting surface due to a sticking of dust and a deterioration of characteristics of the titled element by coating the reflecting surface of a prism with a substance, having a refractive index lower than that of a birefringence substance, thereby totally reflecting the incident light on the reflecting surface. CONSTITUTION:The substance 5 having the lower refractive index than that of the birefringence substance is vapor-deposited on the reflecting surface 3 of the prism 1 composed of the birefringence substance. The total reflection is carried out due to the difference of the refractive index of the birefringence substance and that of the substance vapor-deposited on the reflecting surface 3. When silicon dioxide is vapor-deposited on the reflecting surface 3 of the prism 1 composed of a titanium dioxide single crystal, the total reflection may be sufficiently carried out by the difference of the refractive index of the titanium dioxide single crystal and that of silicon dioxide.
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