Two-photon absorption in SiO2- and (SiO2 + GeO2)-based fibres at a wavelength of 349 nm

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass (SiO₂) core and in a fibre with a germanosilicate glass (SiO₂ + GeO₂) core. The two-photon absorption coefficient β measured at a wavelength of 349 nm in the (SiO₂ + GeO₂)-based fibre (13.7 cm TW^-1) multiply exceeds that for the pure quartz glass optical fibre (0.54 cm TW^-1).