Spectral dependence of photorefractive effect in nitrogen-doped silica

Photoinduced variations in the refractive index of nitrogen-doped silica ar e directly measured in the wavelength range from 350 to 2500 nm. It is foun d that the change in the refractive index under the action of 193 nm laser radiation significantly increases in the long-wavelength region and amounts to similar to 10(-3) at lambda = 2.5 mu m (for the energy fluence similar to 10(4) J cm(-2)). This means that the nature of the photorefractive effec t in nitrogen-doped silica is related to photostructural transformations af fecting the phonon part of the optical absorption spectrum.