Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm2 and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm2 is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation.