F-doped and H2-impregnated synthetic SiO2 glasses for 157 nm optics

Optical transmission change and point defect formation by irradiation with F2 excimer laser light (∼10 mJ/cm2/pulse×3.6×105 pulses, λ=157 nm) were examined for four types of synthetic SiO2 glasses: wet (OH content: 1.7×1019 cm−3), dry (OH content: <1×1016 cm−3), F-doped (F content: 2.2×1020–4.2×1020 cm−3, OH content: <1×1016 cm−3), and H2-impregnated (OH content; 1.9×1018 cm−3, H2 content; 1×1018 cm−3) SiO2 glasses. Intense optical absorption bands peaking at 4.8 and 5.8 eV, which are attributed to nonbridging oxygen hole center and E′ center, respectively, and a shoulder at ∼7 eV were induced in the wet and dry specimens after the irradiation. On the other hand, the intensities of absorption bands induced in the F-doped and H2-impregnated specimens were smaller by an order of magnitude than those in other specimens. The internal (reflection-corrected) transmittance at the wavelength of 157 nm for 5 mm thick samples after the irradiation was 87% for the F-doped, 82% for the H2-impregnated, 14% for the wet, and 2.4% for the dry silica glasses. The present results show that F doping or H2 impregnation is an effective way to improve resistance of SiO2 glasses to F2 laser damage.