W. Pötz

COHERENT CONTROL OF OPTICAL GAIN FROM ELECTRONIC INTERSUBBAND TRANSITIONS IN SEMICONDUCTORS

We study electronic transitions between a subband and a lower subband doublet which is driven by a coherent microwave (MW) field in a semiconductor double well structure. Within a microscopic three-band model, we show that variation of the MW phase allows manipulation of the optical gain provided the probe pulse duration is shorter than the period of the MW-field-generated interband polarization in the doublet. Moreover, we find that optical gain without inversion can be achieved in spite of subpicosecond dissipative mechanisms provided by electron-phonon coupling and electron tunneling into and out of the double well.

Self-consistent treatment of resonant-tunneling structures

Abstract The influence of boundary conditions on charge transport through quantum-well heterostructures is studied theoretically. Based on an envelope-function model and stationary scattering theory, a self-consistent treatment is developed to investigate the I–V characteristics of resonant-tunneling structures. Various boundary conditions are discussed. Finally, it is shown how magnetic-field effects can be implemented via suitable boundary conditions.

Coherent control of electron intersubband transitions by frequency-detuned light fields

Abstract We present a brief overview over some of our recent theoretical results regarding coherent control in semiconductor heterostrutures. Three potential schemes for optical coherent control of electron intersubband transitions in semiconductor heterostructures are reviewed. They use the relative phase between two external light fields to manipulate fundamental physical properties, such as absorption, optical gain, final-state population, phonon emission rates, and emission of THz radiation. In this paper we focus on the coherent control of absorption (exciton formation) using two frequency-detuned light fields in asymmetric GaAs/AlGaAs double wells. We show that in the short-pulse regime the change of relative phase amounts to pulse shaping which, in conjunction with excitonic effects, allows substantial control of inter(sub)band transitions. In the long-pulse regime this phase sensitivity is lost, however, charge oscillations between wells can be induced.

Nonequilibrium Phonons And Carrier Cooling In Polar Semiconductors

We present a theoretical study of optical phonon build-up associated with the ultrafast cooling of highly photo-excited electron-hole plasmas in polar semiconductors. Confining ourselves to the study of high carrier concentrations and subpicosecond laser excitation of bulk GaAs and GaAlAs-GaAs single quantum well structures, we find that rather long optical phonon lifetimes are primarily responsible for the experimental observation of reduced carrier cooling rates. The importance of the carrier-carrier interaction, screening, carrier confinement, and slab modes is discussed.

Coherent Control Schemes In Semiconductor Double Wells

We present a brief overview of some of our theoretical studies of coherent control schemes in semiconductor heterostructures within Boltzmann-Bloch equations. The latter are obtained from Dyson’s equation within the Keldysh nonequilibrium Green’s function approach and allow a microscopic analysis of coherent control schemes in semiconductors. Feasibility of coherent control of charge oscillations, optical absorption, and optical gain is predicted. Most recent studies also indicate that coherent control of longitudinal optical (LO) phonon emission rates can be achieved.

Femtosecond Coherent Response of Spin-orbit Split-off Excitons in InP

From spectrally resolved femtosecond four-wave mixing (FWM) in InP at 5 K we observe excitons associated with the spin-orbit split-off gap at 1.52 eV. The FWM spectrum reveals Fano interactions of these excitons with continuum excitations when co-polarized pulses are used. For perpendicularly polarized pulses only weak excitonic features are observed and the spectrum is dominated by the continuum photon echo response.

Transport theory for coupled electron-phonon systems: an independent-particle approach

Abstract It is shown that an important class of coupled electron-phonon systems, in and out of thermal equilibrium, can be described approximately by self-consistent mean-field equations. The relevance of this result to the validity of the scattering picture for nanostructures is discussed.