Abstract:The results of the femtosecond four-wave mixing measurements performed on the CdS crystal at room temperature are reported. The dephasing time T d = 180 fs was obtained. The anti-Stokes shift of the primary photon echo spectrum with respect to the excitation spectrum was observed. The some peculiarities of the coherent responses decay curves indicate that this optical dephasing is due to the exciton-exciton interaction. The stimulated photon echo decay curves appear to have a fast decay component (the time constant of approximately 4.5 ps) in case the energy of exciting pulses exceeds the threshold value of 0.4 μJ. Stimulated photon echo decay curves obtained using various excitation pulses energy
A number of time-resolved optical experiments probing and controlling the spin and charge dynamics of the high-mobility two-dimensional electron gas in a GaAs/AlGaAs heterojunction are discussed. These include time-resolved reflectivity, luminescence, transient grating, magneto-optical Kerr effect, and electro-optical Kerr effect experiments. The optical experiments provide information on the carrier lifetimes and spin dephasing times, as well as on the carrier diffusion coefficient which directly gives the charge mobility. A combination of the two types of Kerr experiment proves to be useful in extracting both the carrier lifetimes and spin dephasing times in a single experiment.
We report femtosecond photon echo and fourwave mixing measurements performed on GaAs/AlGaAs heterostructure at room temperature. In femtosecond photon echo experiment the dephasing time was obtained, found to vary between 40 and 55 fs depending on carrier density. The dependence showed a power-law behavior T2 ∝ N −0.22 , which indicates that major phase coherence loss is due to screened Coulomb electron-electron interaction. Transient grating experiments yielded the electron diffusion coefficient value of 200 cm 2 /s and electron relaxation time equal to 3 ns.Intensity, a.u.
Abstract. We report an experimental study of the intra-and interband transitions in bulk CdS crystal induced by a strong below-band-edge femtosecond laser pulse. An additional peak was observed in spectrally resolved four-wave mixing signal shifted to lower energy and positive time delay.
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