REFRACTIVE-INDEX VARIATION IN PHOTODARKEN ING PROCESS OF SEMICONDUCTOR-DOPED GLASSES

The refractive index variation occurring in semiconductor doped glasse s during the photodarkening process is demonstrated through the measur ement of the Bragg diffraction of a probe beam on gratings photo-induc ed by two interfering pump beams. The refractive index change is attri buted to the Kerr effect created by a static electric field generated inside semiconductor dots by the trapping of one electron in the glass matrix surrounding the nanocrystallite and that of the corresponding hole inside the dot itself. it is also shown that this refractive inde x modification can be anihilated by the creation of an additional elec tron-hole pair, the electron recombining with the previously trapped h ole, the hole being trapped very near the previously trapped electron, thus annihilating the static electric field in the nanocrystallite. T hese permanent gratings might be of interest for volume optical storag e.