@article{23498, abstract = {{The ultrafast dynamics of photoexcitations at silicon surfaces is investigated using a surface-sensitive purely optical technique. In the experiments, the diffracted second harmonic generated by sequences of ultrashort laser pulses is detected as a function of the time delay between the pulses. It is demonstrated that this five-wave-mixing technique can be used to measure the temporal evolution of the optical polarization and the photoexcited populations at the surface. The experimental results can be reproduced by numerical solutions of optical Bloch equations. The theoretical analysis allows one to investigate which dephasing times and relaxation processes are compatible with experiment. Furthermore, it is outlined how one can describe optical nonlinearities at surfaces using a microscopic theory within the framework of semiconductor Bloch equations.}}, author = {{Meier, Torsten and Reichelt, Matthias and Koch, S W and Höfer, U}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, number = {{8}}, pages = {{S221--S244}}, title = {{{Femtosecond time-resolved five-wave mixing at silicon surfaces}}}, doi = {{10.1088/0953-8984/17/8/003}}, volume = {{17}}, year = {{2005}}, } @article{23499, abstract = {{The ultrafast dynamics of photoexcitations at silicon surfaces is investigated using a surface-sensitive purely optical technique. In the experiments, the diffracted second harmonic generated by sequences of ultrashort laser pulses is detected as a function of the time delay between the pulses. It is demonstrated that this five-wave-mixing technique can be used to measure the temporal evolution of the optical polarization and the photoexcited populations at the surface. The experimental results can be reproduced by numerical solutions of optical Bloch equations. The theoretical analysis allows one to investigate which dephasing times and relaxation processes are compatible with experiment. Furthermore, it is outlined how one can describe optical nonlinearities at surfaces using a microscopic theory within the framework of semiconductor Bloch equations.}}, author = {{Meier, Torsten and Reichelt, Matthias and Koch, S W and Höfer, U}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, number = {{8}}, pages = {{S221--S244}}, title = {{{Femtosecond time-resolved five-wave mixing at silicon surfaces}}}, doi = {{10.1088/0953-8984/17/8/003}}, volume = {{17}}, year = {{2005}}, } @inproceedings{44297, author = {{Meier, Torsten and Reichelt, Matthias and Pasenow, B. and Stroucken, T. and Koch, S.W.}}, booktitle = {{2005 annual conference of the German Physical Society (DPG) during the World year of physics}}, location = {{Berlin, Germany}}, title = {{{Optical properties of semiconductor photonic-crystal structures: spatially-inhomogeneous excitonic resonances and optical gain}}}, volume = {{40}}, year = {{2005}}, } @article{23503, author = {{Oszwałdowski, R. and Reichelt, Matthias and Meier, Torsten and Koch, S. W. and Rohlfing, Michael}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{23}}, title = {{{Nonlinear optical response of the Si ( 111 ) − ( 2 × 1 ) surface exciton: Influence of biexciton many-body correlations}}}, doi = {{10.1103/physrevb.71.235324}}, volume = {{71}}, year = {{2005}}, } @article{23512, abstract = {{The optically induced electron dynamics at a Si(001) surface is studied using a five-wave-mixing setup which measures the diffracted second-harmonic intensity induced by three ultrashort (13 fs) laser pulses. Depending on the time ordering of the pulses, this technique is capable of monitoring the temporal evolution of photoexcited one- or two-photon coherences, or populations. For a particular pulse sequence, the experiments show a delayed rise and a decay of the diffracted signal intensity on time scales of 50 and 250 fs, respectively. This response can be described by optical Bloch equations by including rapid scattering of the photoexcited carriers in the D(down)band of Si(001).}}, author = {{Voelkmann, C. and Reichelt, Matthias and Meier, Torsten and Koch, S. W. and Höfer, U.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, number = {{12}}, title = {{{Five-Wave-Mixing Spectroscopy of Ultrafast Electron Dynamics at a Si(001) Surface}}}, doi = {{10.1103/physrevlett.92.127405}}, volume = {{92}}, year = {{2004}}, } @article{43289, abstract = {{A microscopic approach is presented to compute nonlinear optical properties of semiconductor surfaces. The method uses quasiparticle wave functions and dispersions obtained from ab initio band-structure theory as an input for Bloch equations which describe the optical properties. Excitonic effects in the linear absorption spectra of the Si(111)- (2×1) surface are obtained by integrating equations of motion. To demonstrate the applicability of the approach for analyzing nonlinear optical properties, ultrafast light-intensity-dependent absorption changes of the surface exciton are predicted. The numerical results discuss the optical Stark effect and spectral oscillations of the surface exciton which can both be observed in pump-probe experiments.}}, author = {{Meier, Torsten and Reichelt, Matthias and Koch, S.W. and Rohlfing, M.}}, journal = {{Physical Review B}}, number = {{4}}, publisher = {{American Physical Society}}, title = {{{Theory for the nonlinear optical response of semiconductor surfaces: Application to the optical Stark effect and spectral oscillations of the Si(111)-(2x1) surface exciton}}}, doi = {{10.1103/PhysRevB.68.045330}}, volume = {{68}}, year = {{2003}}, } @article{43287, abstract = {{A novel microscopic approach for computing nonlinear optical properties of semiconductor surfaces is outlined. The linear and nonlinear response of the Si(111)-(2×1) surface is studied using a combination of ab-initio band-structure theory and equation of motion technique. The usefulness of the method is shown by reproducing known excitonic effects in the linear differential reflectivity spectrum. To additionally demonstrate the applicability of the approach for the nonlinear regime, the nonlinear optical response in Stark effect configuration is examined.}}, author = {{Meier, Torsten and Reichelt, Matthias and Koch, S.W. and Rohlfing, M.}}, journal = {{physica status solidi (b)}}, number = {{3}}, pages = {{525--528}}, publisher = {{WILEY‐VCH Verlag}}, title = {{{Microscopic theory for the nonlinear optical response of semiconductor surfaces: Application to the optical Stark effect of the Si(111)-(2x1) surface exciton}}}, doi = {{10.1002/pssb.200303180}}, volume = {{238}}, year = {{2003}}, } @article{43296, abstract = {{A three-beam configuration is used to investigate the spectrally resolved wave-mixing signal of a ZnSe single quantum well. The spectrum recorded in direction 2 k2–k1 shows coherent oscillations induced by a delayed third pulse with direction k3. Intensity and polarization-dependent measurements indicate that the signal is generated by a combination of four- and six-wave mixing. The origin of the oscillations can be explained qualitatively by a two-level model. The polarization-dependent experimental results require the treatment of many-body correlations and are well explained by microscopic calculations including four-particle correlations up to fifth order in the fields.}}, author = {{Meier, Torsten and Wagner, H.P. and Tranitz, H.-P. and Reichelt, Matthias and Koch, S.W.}}, journal = {{physica status solidi (a)}}, number = {{3}}, pages = {{843--847}}, publisher = {{WILEY‐VCH Verlag Berlin GmbH}}, title = {{{Coherent Oscillations in Multiwave Mixing Due to Higher‐Order Coulomb Correlations}}}, doi = {{10.1002/1521-396X(200204)190:3<843::AID-PSSA843>3.0.CO;2-B}}, volume = {{190}}, year = {{2002}}, } @inbook{43298, author = {{Meier, Torsten and Reichelt, Matthias and Schlichenmaier, C. and Siggelkow, S. and Thomas, P. and Koch, S.W. and Weiser, S. and Sieh, C.}}, booktitle = {{Germany NIC Series Vol. 9}}, editor = {{Rollnik, Horst and Wolf, Dietrich}}, isbn = {{3-00-009055-X}}, pages = {{ 315--324}}, publisher = {{John von Neumann Institute for Computing}}, title = {{{Many-Body Correlation Effects in Photoexcited Semiconductor Heterostructures}}}, year = {{2002}}, } @article{43309, abstract = {{The nonlinear optical response of a ZnSe single quantum well is investigated by spectrally resolving a wave-mixing signal using a three-beam configuration. A delayed third pulse with direction k3 leads to coherent oscillations in the spectrum emitted in 2k2–k1. Polarization-dependent measurements highlight the importance of higher-order Coulomb correlations as the dominant coupling mechanism between the three pulses. The experimental results are well explained by microscopic calculations including four-particle correlations up to fifth order in the fields.}}, author = {{Meier, Torsten and Wagner, H.P. and Tranitz, H.-P. and Reichelt, Matthias and Koch, S.W.}}, journal = {{Physical Review B}}, number = {{23}}, publisher = {{American Physical Society}}, title = {{{Coherent spectral oscillations in multiwave mixing}}}, doi = {{10.1103/PhysRevB.64.233303}}, volume = {{64}}, year = {{2001}}, } @article{43319, abstract = {{A phenomenological multi-exciton level scheme is used to calculate the excitonic differential absorption as measured in pump and probe experiments. Numerical results are compared to those obtained by a fully microscopic density-matrix theory. For resonant excitation, optimized parameters yield qualitative agreement, but the phenomenological approach soon reaches its limit for non-resonant pumping.}}, author = {{Meier, Torsten and Reichelt, Matthias and Sieh, C. and Koch, S.W.}}, journal = {{physica status solidi (b)}}, number = {{1}}, pages = {{249--252}}, publisher = {{WILEY‐VCH Verlag Berlin GmbH}}, title = {{{Comparison of the differential absorption obtained within a few-level model and the microscopic density-matrix theory}}}, doi = {{10.1002/1521-3951(200009)221:1<249::AID-PSSB249>3.0.CO;2-E}}, volume = {{221}}, year = {{2000}}, }