Patent ID: 6761951
Filing Date: 2004-07-13
Classification: C03B,C03C,Y02P,Y10T

Abstract:
A synthetic quartz glass blank which is obtained by homogenizing a synthetic quartz glass ingot having periodic striae in a direction of growth, has a generally cylindrical shape with a diameter of 150 to 380 mm and a thickness of 50 to 150 mm, and contains substantially no chlorine; wherein the blank has:(a) striae grades in a working direction and an off-axis direction which meet grade A of U.S. military specification MIL-G-174B, (b) a working direction hydroxyl group concentration averaged in the off-axis direction and an off-axis direction hydroxyl group concentration averaged in the working direction of 700 to 1,000 ppm each, (c) a working direction fictive temperature averaged in the off-axis direction and an off-axis direction fictive temperature averaged in the working direction of 850 to 950Â° C. each, and (d) a refractive index distribution &Dgr;n for 633 nm wavelength light in the working direction of the synthetic quartz glass of at most 1Ã—10âˆ’6.