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COROVAI, Alexandru; MANGIR, A.; KHADZHI, Peter. Nonlinear transmission of supershort laser pulses by thin semiconductor films. In: Materials Science and Condensed Matter Physics. Ediția a 9-a, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, p. 87.
|Materials Science and Condensed Matter Physics
Ediția a 9-a, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
Chișinău, Moldova, 25-28 septembrie 2018
Peculiarities of nonlinear nonstationary transmission (reflection) of supershort laser pulse by a thin semiconductor film, depending on the intensities, envelope shapes and widths were investigated taking into account the processes of exciton–photon interaction, optical exciton–biexciton conversion and two–photon biexciton excitation from the ground state of the crystal. We developed the theory for the case when one pulse with the same frequency excites the excitons, biexcitons from the ground state of the crystal and mixes the exciton and biexciton levels. This case is possible for the crystals like CdS or CdSe, where biexciton bindig energy is vanishingly small. The system of nonlinear differential equations is derived, which describes the time evolution of the real and imaginary components of excitons and biexciton polarization of medium and of the amplitudes of transmitted fields through film. The equations for the field amplitudes are the differential ones for the films with the thickness of the order of the wave length, which are converted into the system of algebraic equations for the films with the thickness much less than the wave length. For the short pulses of the rectangular shape we have predicted the nonstationary regimes of the total reflection of the incident pulse, of the total bleaching, of the transformation of a short pulse into the train of supershort pulses, of the generation of solitary supershort pulse, the width of which is of some orders less, than the width of the incident pulse. In the case of the Gaussian incident pulses we obtain the shortening of the transmitted pulses, the generation of several subpulses and occurrence of the selfpulsing regime.