Patent ID: 8498056

Claim:
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, wherein, 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 BR cos2θ xy defined from a birefringence BR and a fast axis direction θ xy as measured from a parallel direction to the principal optical axis direction is defined as an average birefringence AveBR cos2θ 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 Δn in the principal optical axis direction is 2×10 −6 nm/cm or less, and a refractive index distribution Δn in the off-axis direction is 5×10 −6 nm/cm or less, provided that each of the numerical values of BR, θ xy , BR max and Δn is a measured value at a wavelength of 633 nm, and a unit of the birefringence is nm/cm: −1.0≦AveBR cos2θ xy <0.0 (1-1) 0.0≦BR max ≦1.0 (2-1).