Lineare und nichtlineare optische Eigenschaften von ZnSe-basierten Halbleiter-Nanostrukturen im Bereich polaritonischer Zustände

In this work the linear and nonlinear optical properties of ZnSe based heterostructures in the spectral range of polaritonic resonances are experimentally and theoretically investigated. The experimental findings are explained in terms of the phenomenological models and the microscopic theory. The microscopic simulations were performed by Stefan Schumacher, University of Bremen. The experimental transmission spectra of the series of high quality ZnSe/ZnSSe heterostructures with different thicknesses of the ZnSe layers are analysed in the linear optical regime with respect to the polariton modes occurring due to the k-quantization. The outside surfaces of the ZnSSe cladding layers form a Fabry-Perot resonator for the optical field. The resulting Fabry-Perot modes are superimposed to the polariton resonances and must be included in the theoretical description. The phenomenological oscillator model with spatial dispersion and Pekar’s additional boundary condition reproduces the spectra of the samples. The microscopic simulations are based on a direct solution of the coupled evolution equations of the excitonic transition amplitude and of the electromagnetic fields. These calculations in terms of microscopic boundary conditions for the exciton motions within a finite-high confinement potential can explain the measured transmission spectra. The influence of coherent optical nonlinearities on polariton effects is studied by detailed comparison of experiment and theory. Spectral changes that depend on the light polarization are analysed for single pulse transmission and pump-and-probe excitation. The experimental results are in excellent agreement with microscopic description of propagation effects in the nonlinear optical regime based on the dynamics-controlled truncation formalism. The coherent control technique offers the posibility to optically manipulate a quantum mechanical system with regard to both the amplitudes and the relative phases of excitations. In this work the coherent control is achieved by the pair of the phase-locked laser pulses. The coherent manipulation of the polaritonic system in ZnSe/ZnSSe heterostructures is performed in pulse-transmission and four-wave-mixing (FWM) experiments. It is shown in time-resolved pulse transmission that the polariton modes, their quantum beat structure, and the radiative decay can be coherently manipulated. Calculations based on a microscopic polariton theory can explain the experimental findings without the use of fit parameters. The effective decay times of the coherent polarization, which depend on the polariton modes involved and their radiative decay, are extracted on the basis of a phenomenological model. The coherent control of nonlinear polaritonic FWM polarization is different for both directions of first-order diffraction. For the 2k1 − k2 direction the phase-locked pulse pair contributes quadratically to the FWM signal and the separate control of polariton modes is observed. Contrary, in the 2k2 − k1 direction the pulse pair contrubutes linearly to the signal and all polariton modes are only simultaneously controlled. The coherent control of polaritonic FWM polarization in both diffraction directions is explained in terms of the two-polariton coherences and of Pauli blocking.