Optics in the exciton absorption region

Bohdan M. Nitsovich, C. Y. Zenkova

An exciton-phonon mechanism for producing cavityless optical bistability is suggested. We consider the influence of the oscillating subsystem of a crystal on the absorption process of a laser wave in the region of exciton frequencies. It is shown that exciton-phonon interaction leads to nonlinear dependence of the absorption coefficient on the density of the exciton gas. The increase of absorption with increasing exciton density, however, is possible only in the frequency region on the long-wavelength tail of the exiton band. As a result, the exciton density of the crystal becomes a hysteresis function of external parameters (intensity of the incident wave, temperature, etc.). We calculate the absorption coefficient of excitons and define the frequency and temperature regions where optical bistability may exist. We analyze different relaxation mechanisms of excitons and explain the experimental results of observing optical bistability in different semiconductor crystals.

B. S. Razbirin, V. P. Mushinskiǐ, Mustafa Karaman +2 more

J.P. Heritage, A. Von Lehmen, Jane E. Zucker +1 more

We have investigated the optical properties of GaAs quantum wells in the spectral region below the band edge using a two-wavelength picosecond optical pulse technique. Optical pumping in the transparent region produces modulation of the excitonic absorption which is probed with an optical pulse tuned to the excitonic absorption. We identify two distinct physical mechanisms that lead to the absorption modulation. First, a real population of carriers is produced by phonon-assisted absorption. These carriers bleach the excitonic transition by the action of the exclusion principle. The second mechanism involves virtual populations induced by the off-resonant optical excitation.

Eiichi Hanamura

Oleksandr V. Derevyanchuk, Claudia Yu. Zenkova, Valeriy M. Kramar +1 more

The influence of the exciton and phonon spectra of layer semiconductors on the conditions of optical bistability (OB) realization in the exciton absorption region is investigated by means of the Green function method. Using the 2H-polytype PbI2 as an example, it has been found that an effective exciton scattering by an oscillation of the bending wave (BW) type leads to the short wave shift of the OB realization region, the decrease of its size, the widening of the OB observing temperature region and to the shift of the hysteresis loop in the direction of greater intensities, the decrease of its height and width. The possibility of observing the polarizable OB, connected with the direction of spreading and the insident light polarization dependence ofthe layer crystal exciton spectra is substantiated in this paper.

J. J. Hopfield