Synthetic quartz glass with fast axes of birefringence distributed in concentric-circle tangent directions and process for producing the same

Abstract

The present invention provides a synthetic quartz glass having a diameter of 100 mm or more for using in an optical apparatus comprising a light source emitting a light having a wavelength of 250 nm or less, the synthetic quartz glass having, in a region located inward from the periphery thereof by 10 mm or more in a plane perpendicular to the optical axis of the synthetic quartz glass: a birefringence of 0.5 nm or less per thickness of 1 cm with respect to a light having a wavelength of 193 nm; an OH group concentration of 60 ppm or less; an averaged differential OH group concentration from the center of the synthetic quartz glass toward a peripheral direction thereof, normalized with respect to the radius of the synthetic quartz glass, of −8 to +60 ppm; and an unbiased standard deviation a of a differential OH group concentration from the center of the synthetic quartz glass toward a peripheral direction thereof, normalized with respect to the radius of the synthetic quartz glass, of 10 ppm or less, the unbiased standard deviation a being determined with the following formula (1): σ = ∑ i = 1 n  ( X i - X _ ) 2 n - 1   providing  ;   X i = Δ   n _ OH   i Δ   r i * = n _ OH   i - n _ OH   i + 1  r i * -  r i + 1 * ( 1 ) : differential OH group concentration at measurement point i normalized with respect to the radius R of the synthetic quartz glass; n _ OH   i = n OH   i - 1 + n OH   i + n OH   i + 1 3 : OH group concentration at measurement point i in terms of moving average for three points including the two points before and after the measurement point i;  r i * = r i R : radius at measurement point i normarized with respect to the radius R of the synthetic quartz glass; X : average of OH group concentrations Xi in the whole evaluation region; and n : number of measurement points in the evaluation region (integer of 2 or more).

Dependencies are inferred from the claim text.