SYNTHETIC QUARTZ GLASS WITH FAST AXES OF BIREFRINGENCE DISTRIBUTED IN CONCENTRIC-CIRCLE TANGENT DIRECTIONS AND PROCESS FOR PRODUCING THE SAME

摘要

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): $\begin{array}{cc}\mathrm{sigma}=\sqrt{\frac{\sum _{i=1}^n{\left(X_i-\stackrel{\_}{X}\right)}^2}{n-1}}\mathrm{providing};X_i=\frac{\mathrm{Delta}{\stackrel{\_}{n}}_{\mathrm{OH}i}}{\mathrm{Delta}r_i^{*}}=\frac{{\stackrel{\_}{n}}_{\mathrm{OH}i}-{\stackrel{\_}{n}}_{\mathrm{OH}i+1}}{r_i^{*}-r_{i+1}^{*}}& \left(1\right)\end{array}$ : differential OH group concentration at measurement point i normalized with respect to the radius R of the synthetic quartz glass; ${\stackrel{\_}{n}}_{\mathrm{OH}i}=\frac{n_{\mathrm{OH}i-1}+n_{\mathrm{OH}i}+n_{\mathrm{OH}i+1}}{3}$ : 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; $r_i^{*}=\frac{r_i}{R}$ : 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).