| 摘要 |
<p>In order to provide a silica glass optical material having a high initial transmittance, a small fluctuation in refractive index DELTA n, and an excellent durability to long term irradiation with radiations with a wavelength of 155 to 195 nm from excimer lasers and excimer lamps, a silica glass optical material is suugested which is characterized in that it is of ultrahigh purity, contains from 1 to 100 wtppm of OH groups, from 5 x 10<16> to 5 x 10<19> molecules/cm<3> of H2, and from 10 to 10,000 wtppm of F, but is substantially free from halogens other than F, and has a fluctuation in refractive index, DELTA n, in the range of from 3 x 10<-6> to 3 x 10<-7>.</p> |
