| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to mold optical elements, such as Fresnel lenses, having fine patterns without fusing and cracking, by press-forming a glass blank in a heat softened state with a pair of upper and lower molds and parting the one surface of the glass blank formed by the forming surfaces of mold members from the molds at a temp. corresponding to a specific glass viscosity or above. SOLUTION: This process for production consists of producing the optical elements, such as concave lenses and more particularly diffraction gratings and Fresnel lenses, having the fine patterns without the occurrence of craze and crack. More particularly in the press forming of the optical elements having the fine patterns on one surface, the coefft. of thermal expansion of the glass at the time of parting is larger than that of the mold members and the parting of the surface of the fine patterns is execute by opening the molds at the temp. corresponding to 10<12> dPaS in glass viscosity or above in order to prevent the glass from being held by the ruggedness of the mold surfaces. The forming surfaces of the upper mold member having the fine patterns is preferably coated with a hard carbon film, etc., and the forming surface of the lower mold member is preferably composed of TiN, SiC or noble metals. The fine patterns are rugged shapes of 0.1 to 50μm.
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