Kinetics modeling in photosensitive glass

Kinetics of photoinduced process is studied in a new photosensitive material for volume hologram recording which is a photo-thermo-refractive glass (PTRG). A system of balance equations is derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+). The main approach for the system solution is a calculation of low quasistationary concentration of free electrons in a conduction band, while concentrations of generated electron and hole centers are expected to be variable. A general solution of a system is found as a combination of exponential and hyperbolic functions. It is shown that an exponential solution is the result of the absence of a re-trapping of electrons, while a pure hyperbolic solution occurs in the case of equal probability of trapping and re-trapping. The approach developed for the first stage of photo-thermo-refractive process which is photoionization and trapping, is applied for the modeling of the final result of the whole process of photo-thermo-induced refractive index transformation in glass. It is found that the refractive index increment in PTRG is better described by hyperbolic function compare to the exponential one. Kinetic parameters of induced refraction in PTRG are determined. (C) 2003 Published by Elsevier B.V.