摘要:

AbstractRecent results on femtosecond time‐integrated and time‐resolved four‐wave‐mixing experiments in intrinsic and modulation‐doped GaAs quantum wells are reported. A variety of new phenomena ranging from giant excitonic resonance for intrinsic samples, Fermi liquid behavior in modulation‐doped samples, and interesting temporal evolutions provide new insights into the physical process responsible for the coher

ISSN:0370-1972    

DOI:10.1002/pssb.2221730102

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractFemtosecond nonlinear laser spectroscopy is applied to study the dynamics of coherent optical excitations in semiconductors. In particular, excitonic excitations in quantum wells and superlattice structures are considered. Two examples demonstrate that four‐wave mixing experiments with time‐resolved detection of the nonlinear signal are able to distinguish between quantum beats and polarization interfere

ISSN:0370-1972    

DOI:10.1002/pssb.2221730103

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTime‐resolved measurements of transmission in resonance with the 1 S quadrupole polariton in Cu2O reveal a long‐lasting signal which is modulated by pronounced oscillations with time‐dependent period. These oscillations are interpreted as “propagation beats”, which are caused by superposition of excited states of both polariton branches which propagate coherently through the crystal. At higher excitation intensities the decay becomes faster and the beats disappear. Magneto‐quantum beats are also influenced significantly by propagation effects in transmission m

ISSN:0370-1972    

DOI:10.1002/pssb.2221730104

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCoherent pulse breakup is observed for below‐exciton resonance femtosecond excitation in a room‐temperature GaAs/AlGaAs multiple quantum well waveguide using the cross‐correlation technique. This pulse breakup is present only for large area pulses with durations less than the dephasing time of the closest exciton. For pulses longer than the exciton dephasing times, but with the same and even larger areas, the pulse breakup is not observed. The breakup is due to neither self‐induced transparency nor temperoral soliton. Instead, calculations based on the coupled semiconductor Maxwell‐Bloch equations show that coherent self‐phase modulation during propragation drives the system out of the initial adiabatic following regime into oscillatory excitation density, and eventually, pulse shape

ISSN:0370-1972    

DOI:10.1002/pssb.2221730105

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractPicosecond lasers allow to detect the dynamics of excitons directly in the time domain. Here examples of such experiments are presented for high quality AlGaAs MQW samples at low temperatures and in the low and medium density regime. The phase relaxation timeT2is measured in FWM experiments and quantum beats are observed between the hh and lh exciton and between exciton and biexciton states. A value of the biexciton binding energy of 1.75 meV is deduced in agreement with our luminescence data. TheT2times are compared with scattering times τ obtained from diffusion measurements using ps and ns laser‐induced gratings. Interface‐roughness scattering occurs only for thermalized excitons. The influence of increasing exciton‐exciton scattering with density is demonstrated for (magneto‐) excitons and Landau levels. Finally the luminescence dynamics of excitons is investigated for resonant and nonresonant excitation. The influence of cooling (intraband relaxation) is discussed and a simple model is presented to explain the generally observed increase of the lifetimeT1with lattice tem

ISSN:0370-1972    

DOI:10.1002/pssb.2221730106

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractDynamics of free and bound excitons in CdSe and localized excitons in CdSexS1−xare studied by degenerate four‐wave mixing and light‐induced grating experiments. In the coherent range, the dephasing of excitons is determined as a function of temperature, density and energy. For incoherent excitons, recombination lifetimes and diffusion coefficients are determined. In particular, the mobility of excitons in CdSexS1−xnear the mobility edge is

ISSN:0370-1972    

DOI:10.1002/pssb.2221730107

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIt is demonstrated that the exciton–photon coupling, or equivalently the polariton nature of the exciton, may lead to qualitative changes in the lineshape of time‐resolved four‐wave mixing. For small oscillator strength and hence small longitudinal–transverse splitting this coupling acts very similar to the recently discovered coherent exciton–exciton interaction, i.e. as an exponential rise of the time‐integrated signal for negative time delay. Here the exciton–photon coupling can be interpreted as a mediated exciton–exciton interaction. For larger coupling a distinct nonperiodic modulation evolves that reflects the oscillation between the two branches of the polariton dispersion. Spectrally and time‐resolved four‐wave mixing is shown to give direct access to the dynamics on the two branches. Corresponding femtosecond experiments on two‐dimensional magneto‐excitons are compared with

ISSN:0370-1972    

DOI:10.1002/pssb.2221730108

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractExperiments and a theoretical description of the optical intraband Stark effect in multiple quantum wells for an in‐plane polarization of pump and test fields are presented. The nonlinear absorption spectra show a pronounced dependence on the angle between pump and test field polarization. For a quantitative agreement between theory and experimental results it is necessary to take the inhomogeneous distribution of the pump field into account, which is due to multiple reflections of the CO2laser beam in the sampl

ISSN:0370-1972    

DOI:10.1002/pssb.2221730109

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractBy observing quantum beats in the self‐diffracted signal from a nonlinear mixing process in a crystal, and by spectrally resolving this signal, information is obtained about solid state parameters, such as energy splittings and energy shifts. This technique is used to study bound excitons in CdSe with a strong, resonant third‐order susceptibility. Furthermore, in the region of free exciton propagation, effects on the third‐order nonlinear polarization are observed and explained by quantum beats between propagating polar

ISSN:0370-1972    

DOI:10.1002/pssb.2221730110

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe time‐resolved resonant light scattering spectrum following short pulse excitation provides information on the various inelastic (energy relaxation) and elastic (phase relaxation) relaxation processes of an exciton system. Taking properly the implications of the measurement process into account this can be exploited to discriminate between Raman scattering processes, proceeding without loss of coherence, and hot luminescence, occurring after phase relaxation. The coherent nature of the states can be directly revealed by quantum beats in the time‐dependent scattering spectrum if the resonant states are energetically split. Such experiments are presented for bound excitons in CdS and the lowest exciton‐polariton in Cu2O. These measurements allow to deduce refined magneto‐optical parameters due to the high energy resolution of this method. The exciton dephasing times found are surprisingly long (up to 1 ns) and determined by energy relaxation due to phonon scattering. Pure dephasing due to elastic scattering gives only a minor contr

ISSN:0370-1972    

DOI:10.1002/pssb.2221730111

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY