D. K. Okorokov

Strong optical nonlinearities and laser emission of semiconductor microcrystals

Changes in the transmission of quasi-zero-dimensional CdSe microcrystals (quantum dots) induced by ultrashort laser pulses were investigated with picosecond time resolution. The transitions between the energy levels of electrons and holes spatially confined within microcrystals were observed as bleaching bands in nonlinear transmission spectra. Gain registered at the transitions between the lowest levels of size quantization in microcrystals allowed to achieve the regime of laser generation in Fabry-Perot resonator made of glass containing semiconductor microcrystals.

Time-resolved nonlinear spectroscopy of semiconductor microcrystals (quantum dots)

Transmission spectra recovery and time-resolved luminescence of CdSe microcrystals optically excited by ultrashort laser pulses have been studied with picosecond time resolution. The transitions between levels of electrons and holes spatially confined within microcrystals were observed as bleaching bands in nonlinear transmission spectra. The significant shortening of the carrier lifetime in microcrystals of smaller size was detected. The regime of laser emission at the transition between the lowest levels of size quantization was achieved.

Resonant Nonlinearities and Optical Bistability in Semiconductors

Changes in the absorptive and refractive index caused by absorption of laser light in CdS and GaSe semiconductors (“dynamic” nonlinearities which may lead to optical bistability) were investigated. Nonlinear effects may be very large (strong nonlinearities) due to the resonant enhancement near the sharp band edge. In this case optical properties can be varied significantly by creating small numbers of interacting free carriers, free and bound excitons, biexcitons, etc. The interplay of optical nonlinearity and feedback leads to optical bistability (OB) - the existence of two stable output states of an optical system for the same input parameters. OB allows one to reproduce the operational modes of electronic devices (amplification, switching, memory, logical operations) by purely optical means.

Nonlinear optical phenomena and lasing in semiconductor quantum dots and wires

Transmission spectra recovery of CdSe, CdSxSe1-x nanocrystals and porous silicon wires optically excited by ultrashort laser pulses have been studied with picosecond time resolution using pump and probe technique. The transitions between levels of electrons and holes spatially confined within nanocrystals and thin wires were observed as bleaching bands in nonlinear transmission spectra (saturation effect). Spectra and values of third order resonant susceptibility were determined for nanocrystals of different size and porous silicon using the experimentally measured differential transmission spectra.