METHOD FOR ANNEALING FLUORITE SINGLE CRYSTAL

摘要

PROBLEM TO BE SOLVED: To obtain a signal having the good homogeneity of a refractive index by annealing a fluorite single crystal worked in such a manner as to have a plane contour shape approximate or analogous or approximately approximate or approximately analogous to or with the plane contour shape of the final product. SOLUTION: The ingot of the fluorite single crystal produced by a Bridgman method is used. The blank cut out of the single crystal ingot is first rounded to have the plane contour shape approximate or analogous or approximately approximate or approximately analogous to or with the plane contour shape of the final product. The blank is so worked that the refractive index distribution of the fluorite single crystal after the working has rotational symmetry to an optical axis. The single crystal is then annealed to obtain the fluorite single crystal of <=5×10<-6> in the refractive index differenceΔn <=0.015λin the RMS value after the power component correction of a wave front aberration and <=0.04λin the RMS value in the non-rotationally symmetrical component in the optical axis direction is obtd. The working method is particularly effective for the large-diameter fluorite single crystal of the diameter, max. diameter or max. size exceeding 200mm.