Nonlinear excitation of AgBr nanocrystals in the field of short light pulses

Abstract

Processes of the electron-hole pair generation and excited-state relaxation at earlier stages of the latent image formation in the AgBr nanocrystals are studied theoretically. The experimental dependence of the photographic blackening D in the field of the intense laser light on the light pulse energy I is analyzed in the range of pulse durations τi from 10−13 to 10−8 s. The values of I needed to obtain a fixed blackening D at τi∼10−10 s exceeded those at τi∼10−8 s by three orders of magnitude. However, as τi further decreased to hundreds of fs, these values decreased by two orders of magnitude. It is shown that experimental nonmonotonic dependences can be explained by saturation of the one-photon interband generation of electron-hole pairs accompanied by the development of the two-photon generation. For shortest pulses and, correspondingly, greatest light intensities, the pair generation rate varies more strongly than upon usual two-photon absorption, which is caused by the resonance optical Stark effect.