We calculate the dielectric function of three-level systems like CuCl under high pulsed excitation in the nanosecond time scale. We find a memory effect of the crystal absorption and dispersion which is mainly due to the radiative lifetimes of the biexcitons created during the pulse.
The theoretical study of the nonlinear dielectric function of three-level systems has shown a memory effect which depends on the inversion of the exciton and biexciton populations created during the excitation and on the relaxation times of these quasiparticles. This effect is studied at low temperatures (2 K) by measuring the time evolution of the transmission of a beam through a CuCl sample. In addition, it has important consequences on the switching properties of bistable devices using CuCl as the active medium.
We study the time variation of the nonlinear absorption due to the creation of biexcitons by a high-intensity nanosecond pulsed laser in CuCl. We show that this variation is different at the beginning and at the end of the laser pulse. This memory effect depends on the photon energy and on the intensity of the laser beam. An explanation based on the time dependence of the population is suggested. We also make a time analysis of a bistable device composed of a sample of CuCl placed in a Fabry-Pérot cavity. The switching times measured are of some hundredths of picoseconds. We stress the importance of the absorption present in the cavity and show that it may destroy the dispersive bistability. Finally, we give some trends of the spatial variation of hysteresis in the transverse section of the laser beam.
We study the temporal and spatial evolution of a pump, test, and signal field generated in a four-wave-mixing process for resonant excitation of a nonlinear medium by nanosecond pulses. The propagation effects for the pulses are taken into account beyond the usual mean-field approximation. The model is then applied to a three-level system, describing CuCl at low temperatures. A great deal of new information concerning the temporal and spatial structures of the different fields propagating through the sample is obtained. We show, for instance, that the temporal shapes of the interacting fields are well established after propagation through the first few micrometers of the sample. Beyond this, they propagate with a diminishing amplitude. We also show that these structures are due to the dephasing of the fields throughout their propagation as well as to the temporal evolution of the absorption and generation function of the sample.