We report the study of optical dephazing Wannier-Stark ladder excitations in a semiconductor superlattice by means transient degenerate four-wave mixing. observe pronounced modulations signal with time period varying linearly electric field. The is found to equal temporal periodicity Bloch oscillations, agreement theory. In addition, we find that decreases increasing localization states, which attributed carrier escape out lowest miniband.

A detailed calculation of the amplitude and phase response ultrathin ZnTe GaP electro-optic sensors is presented. We demonstrate that inclusion dispersion second-order nonlinearity essential. Significant structures in experimental data can be explained by theoretical function. Correcting for detector characteristics, we determine precise shape electromagnetic transients with a time resolution 20 fs. In addition, show ultrafast transport photocarriers semiconductors act as an efficient source...

We directly observe the electromagnetic radiation emitted by electrons coherently oscillating between two wells of a semiconductor coupled-quantum-well structure. Using time-resolved coherent detection submillimeter-wave from these spatial charge oscillations, we trace up to fourteen oscillations at 1.5 THz before phase relaxation destroys coherence wave packet. In addition oscillatory signal, also an instantaneous signal electric-field-induced optical rectification in

The basic concepts of sum frequency generation are reviewed and its application to the measurement time-resolved luminescence spectra with subpicosecond time resolution is discussed. emphasis on discussion those aspects which important for optimization such an upconversion spectrometer. Results numerical calculations presented various nonlinear crystals, a recently developed system reviewed. This provides excellent (<400 fs), wide spectral range, large dynamic allows determination absolute...

We report the first direct determination of carrier-energy-loss rates in a semiconductor. These measurements provide fundamental insight into carrier-phonon interactions semiconductors. Unexpectedly large differences are found energy-loss for electrons and holes GaAs/AlGaAs quantum wells. This difference results from an anomalously low electron-energy-loss rate, which we attribute to presence nonequilibrium optical phonons rather than effects reduced dimensionality or dynamic screening.

We report the first direct observation of nonthermal photoexcited carrier distributions in GaAs quantum-well structures. present experimental studies which show that these thermalize within 200 fs. In addition we are able to near band edge effect long-range Coulomb screening on bleaching two-dimensional-exciton resonances is much weaker than Pauli exclusion principle.

Time-resolved measurements of optically induced changes in the near-band-gap transmission spectrum GaAs at 80\ifmmode^\circ\else\textdegree\fi{}K, following excitation with an ultrashort laser pulse, provide a means directly monitoring hot-carrier distribution as it cools to lattice temperature time constant 4 psec. Exciton screening and band-gap renormalization are observed occur less than 0.5

We have obtained a coherent understanding of spin relaxation processes electrons, holes, and excitons in quantum walls by investigating subpicosecond dynamics luminescence polarization. show that the behavior for electrons holes quasi-two-dimensional systems is distinct from bulk semiconductors many-body effects formation process play an important role exciton relaxation.

We present the first study of dynamics an extended electronic wave packet in a solid. The is created GaAs/AlGaAs double-quantum-well structure by ultrashort pulse excitation. observe oscillatory motion between two wells using time-resolved degenerate four-wave-mixing and pump-and-probe spectroscopy.

We report a slow rise of luminescence in GaAs following subpicosecond photoexcitation and show that it results from return electrons the L to \ensuremath{\Gamma} valley. By fitting our data with an ensemble Monte Carlo calculation, we determine \ensuremath{\Gamma}-L deformation potential be (6.5\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}${10}^{8}$ eV/cm. returning valley act as source heating for photoexcited plasma. further importance electron-electron scattering...

Relaxation of a nonequilibrium distribution electrons and holes in GaAs following femtosecond photoexcitation is investigated via spectrally time-resolved luminescence. A rapid onset luminescence over broad spectral range shows that both are redistributed wide energy within 100 fs, even at excitation densities as low ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The data demonstrate carrier-carrier scattering rates higher than predicted by calculations with statically screened...

We show that excitons form with a time constant \ensuremath{\tau}\ensuremath{\le}20 ps following the creation of electron-hole pairs by subpicosecond optical excitation. The are initially formed in large-wave-vector states. At low temperatures, these nonthermal relax \ensuremath{\approxeq}400 to K\ensuremath{\approxeq}0 states, which couple directly light interaction other and acoustic phonons. This leads slow rise exciton luminescence an unusual dependence this on temperature, excitation...

We present a comprehensive investigation of the dynamics resonantly excited nonthermal excitons in high-quality GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple-quantum-well structures on picosecond time scales. The was investigated using luminescence upconversion technique with two independently tunable, synchronized dye lasers, which allowed measurements evolution polarized resonant 4-ps resolution. show that from initial distribution to...

This paper reviews hot carrier effects in quasi-2-D polar semiconductors (quantum wells and heterostructures), with special emphasis on the GaAs/AlGaAs system. After briefly introducing basic concepts physics, we discuss theoretical calculations of carrier-phonon interactions energy loss rates to lattice systems. We then how these quantities are affected by degeneracy, plasma effects, phonons. The bulk is devoted a discussion experimental results their analysis. Three kinds experiments...

We report the observation of quantum beats in decay coherent polarization intrinsic excitations GaAs/GaAlAs wells. The beating arises from interference excitons with slightly different confinement energy due to well width fluctuations.

We report the first observation of radiative recombination from photoexcited hot carriers in GaAs. Our results show that have an effective temperature which implies a Maxwellian distribution. This increases with excitation intensity. An empirical relationship between this and power transferred to lattice is quantitative agreement theoretical predictions for carrier scattering by polar optical modes.

Four-wave-mixing signals from excitons in high-quality GaAs quantum wells show an unusually slow temporal evolution, stark contrast to the behavior expected for a noninteracting two-level system. We that Coulomb interaction effects, generally neglected analyses of four-wave-mixing experiments, dominate by 2 orders magnitude. Numerical calculations based on extended optical Bloch equations semiconductors provide good qualitative agreement with data.

We have directly measured the tunneling times in an asymmetric coupled double-quantum-well structure using subpicosecond luminescence spectroscopy. observe a strong dependence of nonresonant on barrier thickness. The most striking feature data is drastic reduction time and then further increase as applied electric field sweeps electron levels two wells through resonance. resonant considerably longer than estimated coherent time.

The perpendicular transport of photoexcited electrons and holes in graded-gap GaAs-AlGaAs superlattices is directly determined by subpicosecond luminescence spectroscopy. We show that the electron hole through extended, Bloch-type states for superlattice periods 40 A\r{}, determine mobility such transport. Increasing period to 60 A\r{} reduces a factor 20, resulting from an order magnitude reduction miniband width. Our results also provide first evidence diffusion enhanced potential steps.