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We report large polarization state rotations of a weak pulsed beam in CdTe/CdMnTe quantum wells photoinduced by intense circularly polarized pulsed pump beam. Time-resolved analysis of the effect shows that, at moderate pump fluences, the polarization state rotation is due to the combined effect of many-body interactions and spectral hole burning at early times and to photoinduced magnetization at longer ones. At higher pump fluences, space filling and degenerate four-wave mixing become important. At low pump fluences (few μJ/cm2) already the polarization rotation photoinduced at early times can be as large as a few degrees making these multiple quantum wells potential candidates for applications.

Time‐resolved Faraday rotation measurements on a nanosecond time scale are performed for Cd1−xMnxTe samples grown by two different techniques. The dependence of the observed photoinduced dynamics on the purity, Mn++ concentration (x=0.03, 0.10, 0.15, 0.3), excitation density, and temperature (100–290 K) reveals several novel features. The relaxation for pure samples is monoexponential at 100 K and is slowing down with increasing temperature, in strong contrast to impure samples, where the opposite behavior is observed. All experimental observations can be well explained in a simple model based on rate equations for the free‐carrier populations, provided that recombination centers and impurity traps are included in the model.

Large photoinduced Faraday rotations of the polarization direction of a probe beam traveling through a semimagnetic semiconductor are obtained at temperatures higher than that of liquid nitrogen when a pump pulse is sent through the material. These rotations are quasiproportional to the photoinduced free‐carrier density and the applied magnetic field and are strongly resonant with the band‐gap‐probe frequency detuning. A model based on the free‐carrier induced saturation of the refractive indices explains well the experimental observations. The high values obtained for the photoinduced polarization rotations (more than 1° pJ−1 μm2) make such a process attractive for the design of optical signal processing devices.

International audience; Kerr and four-wave mixing spectroscopy is shown to be a powerful technique to quantify the strong enhancement of the third-order optical nonlinear susceptibilities at the band edge of photonic crystals. Local field factors of about 5 are demonstrated for crossed Kerr effect and a narrow resonance peak observed for the conjugate reflectivity. Moreover, a reduction of the effective nonlinear susceptibility of the four-wave mixing process with increasing pump intensities is measured, which is due to different Kerr-induced blueshifts of the band edge for forward and backward pump beams and signal and conjugate beams. This observation definitely demonstrates the need for considering all the nonlinear processes for the optimization of nonlinear photonic crystals for a given application in optical signal processing

Through intracavity degenerate four‐wave interaction the reflectivity of the phase‐conjugated signal is shown to exhibit bistability and hysteresis when the driving pump field is varied in a continuous matter. The nonlinear medium inside the Fabry‐Perot cavity may be in one‐ or two‐photon resonance with the pump. We suggest suitable materials and discuss possible applications of the bistable response of the reflectivity.

Using time‐resolved techniques, absorption recovery, and degenerate four‐wave mixing, we directly observe the nonexponential intensity‐dependent recombination of free carriers photoexcited in semiconductor‐doped glasses. We assign this behavior to Auger recombination.

Intracavity nearly degenerate four‐wave mixing has been demonstrated by injecting a low intensity probe beam of frequency ω−δω inside a (GaAl)As semiconductor laser operating above threshold at the pump frequency ω. Conjugated reflectivities as high as 5000 together with a 25% energy conversion efficiency are reported with only a few milliwatt pump power. Additional peaks related to the ac stark effect have been observed at a detuning which depended on the pump power. This process could be useful for the study of instabilities occurring in lasers as well as for optical amplification in laser diodes.