| 摘要 |
<p>The present invention provides a synthetic silica glass for optical member in which not only a fast axis direction in an optical axis direction is controlled, and a birefringence in an off-axis direction is reduced, but a magnitude of a birefringence in the optical axis direction is controlled to an arbitrary value. The present invention relates to a synthetic silica glass for optical member to be used within an optical apparatus using light having a wavelength of 250 nm or less as a light source, in which, in an optically effective area within a vertical plane to a principal optical axis direction of the optical member, an average value of a value BRcos2¸ xy defined from a birefringence BR and a fast axis direction ¸ xy as measured from a parallel direction to the principal optical axis direction is defined as an average birefringence AveBRcos2¸ xy , and when a maximum value of a birefringence measured from a vertical direction to the principal optical axis direction of the optical member is defined as a maximum birefringence BR max in an off-axis direction, the following expression (1-1) and expression (2-1) are established, and a refractive index distribution ”n in the principal optical axis direction is 2 × 10 -6 nm/cm or less, and a refractive index distribution ”n in the off-axis direction is 5 × 10 -6 nm/cm or less, provided that each of the numerical values of BR, ¸ xy , BR max and ”n is a measured value at a wavelength of 633 nm, and a unit of the birefringence is nm/cm: - 1.0 ‰¤ AveBRcos �¢ 2 �¢ ¸ xy < 0.0 0.0 ‰¤ BR max ‰¤ 1.0</p> |
