Vacuum-ultraviolet laser-induced refractive index change of fused silica

Increases as large as 0.036–0.038 in the refractive index of fused silica induced by multi-wavelength irradiation of substrates by vacuum-ultraviolet VUV.light emitted from a VUV Raman laser are reported. The index change is ascribed to photoinduced decomposition of Si–O bonds in fused silica by the VUV beam irradiation. The modified areas are practically invisible in optical microscope and atomic force microscope observations. The modified depth is estimated to be about 0.53–0.62 mm. Efficient phase gratings are created by illuminating the substrates through periodically patterned contact masks. q1998 Elsevier Science B.V.