Two-photon optical absorption in amorphous materials

One- and two-photon absorption spectra in some glasses have been studied comparatively. In As2S3, the two spectra show similar shapes, which is pointed out also for SiO2. Two-step absorption occurs upon sub-gap excitation. These glasses exhibit a universal non-linear refractivity. In PbO–SiO2, two-photon absorption appears at a photon energy of ∼2/3 of the bandgap energy, and the absorption increases with the PbO content. The linear and non-linear absorption characteristics in these glasses are discussed taking electronic structures and resonant absorption processes into account.