This invention relates to an optical member made of highly transparent, high-purity synthetic silica glass, to a method for manufacturing a blank or an optical member of such glass, and to the optical members themselves. The optical members have an absolute refractive index, n.sub.d, of 1.460 or more and a hydrogen molecule concentration of at least 5.times.10.sup.16 molecules/cm.sup.3 uniformly distributed throughout the glass and are particularly well suited for use in apparatus in which they are exposed to a high-power laser beam such as that produced by an excimer laser.