Optical member, process for producing the same, and projection aligner

摘要

The optical member of the present invention is an optical member comprising a fluoride crystal; and having an optical axis forming an angle of 10° to 36° with a <111> axis of the fluoride crystal, and a birefringence of 2.0 nm/cm or less in the optical axis direction. The optical member of the present invention can improve the yield and processing accuracy in the process of making the optical member, and can achieve sufficiently high optical characteristics.