Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma

We investigate photoluminescence from a high-density electron-hole plasma in semiconductor quantum wells created via intense femtosecond excitation in a strong perpendicular magnetic field, a fully-quantized and tunable system. At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. In addition, changes in the linewidth, carrier density, and magnetic field scaling of the PL spectral features correlate precisely with the onset of random directionality, indicative of cooperative recombination from a high density population of free carriers in a semiconductor environment

Cooperative recombination of electron-hole pairs in semiconductor quantum wells under quantizing magnetic fields

Journals published by the American Physical Society can be found at http://journals.aps.org/We present results of detailed investigations of light emission from semiconductor multiple quantum wells at low temperatures and high magnetic fields excited by intense femtosecond laser pulses. The intensity and linewidth as well as the directional and statistical properties of photoemission strongly depended on the magnetic field strength and pump laser fluence. We also investigated the effects of spot size, temperature, excitation geometry, and excitation pulse width on the emission properties. The results suggest that the initially incoherent photoexcited electron-hole pairs spontaneously form a macroscopic coherent state upon relaxation into the low-lying magnetoexcitonic states, followed by the emission of a superfluorescent burst of radiation. We have developed a theoretical model for superfluorescent emission from semiconductor quantum wells, which successfully explained the observed characteristics

Constraints on the extremely high-energy cosmic ray accelerators from classical electrodynamics

We formulate the general requirements, set by classical electrodynamics, on the sources of extremely high-energy cosmic rays (EHECRs). It is shown that the parameters of EHECR accelerators are strongly limited not only by the particle confinement in large-scale magnetic fields or by the difference in electric potentials (generalized Hillas criterion) but also by the synchrotron radiation, the electro-bremsstrahlung, or the curvature radiation of accelerated particles. Optimization of these requirements in terms of an accelerator's size and magnetic field strength results in the ultimate lower limit to the overall source energy budget, which scales as the fifth power of attainable particle energy. Hard gamma rays accompanying generation of EHECRs can be used to probe potential acceleration sites. We apply the results to several populations of astrophysical objects-potential EHECR sources- and discuss their ability to accelerate protons to 10(20) eV and beyond. The possibility of gain from ultrarelativistic bulk flows is addressed, with active galactic nuclei and gamma-ray bursts being the examples

Infrared generation in low-dimensional semiconductor heterostructures via quantum coherence

A new scheme for infrared generation without population inversion between subbands in quantum-well and quantum-dot lasers is presented and documented by detailed calculations. The scheme is based on the simultaneous generation at three frequencies: optical lasing at the two interband transitions which take place simultaneously, in the same active region, and serve as the coherent drive for the IR field. This mechanism for frequency down-conversion does not rely upon any ad hoc assumptions of long-lived coherences in the semiconductor active medium. And it should work efficiently at room temperature with injection current pumping. For optimized waveguide and cavity parameters, the intrinsic efficiency of the down-conversion process can reach the limiting quantum value corresponding to one infrared photon per one optical photon. Due to the parametric nature of IR generation, the proposed inversionless scheme is especially promising for long-wavelength (far- infrared) operation.Comment: 4 pages, 1 Postscript figure, Revtex style. Replacement corrects a printing error in the authors fiel

Mode-Locked Dual-Wavelength Heterolasers for Terahertz Generation via Intracavity Wave Mixing

It is shown that the mid/far-infrared (IR) and THz pulse generation via intracavity difference-frequency mixing in quantum-well dual-wavelength heterolasers can be rather efficient under mode-locking regime for one or both lasing fields even at room temperature. In a simple model we derive an explicit formula for intensity of the generated IR or THz pulse and find that this method is capable of producing picosecond pulses at ≈1 GHz repetition rate with the peak power of the order of 1 W and ≤ 0.2 mW at 10 μm and 50 μm wavelengths, respectively

Far-Infrared Few-Cycle-Pulse Generation in Quantum-Well Heterostructures under Femtosecond Laser Pumping

It is shown that the resonant nonlinear-wave mixing in the semiconductor quantum wells under a femtosecond optical pulse excitation can be used for the generation of the utmost short mid/far-infrared pulses with a few- or even single-cycle duration defined by pump duration

Far-Infrared Few-Cycle-Pulse Generation in Quantum-Well Heterostructures under Femtosecond Laser Pumping

It is shown that the resonant nonlinear-wave mixing in the semiconductor quantum wells under a femtosecond optical pulse excitation can be used for the generation of the utmost short mid/far-infrared pulses with a few- or even single-cycle duration defined by pump duration