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AbstractNarrow band emissions at 2.6–2.8 THz are observed out of liquid helium cooled 1 mm disk chips prepared of a wafer with the very low n type doped weak barrier GaAs–GaAlAs superlattice of 1000 periods. The emissions are at about 8.0–18.0 V pulsed voltage applied to the chips in region of the chips positive DC differential conductivity that guaranties absence of inhomogeneous electric field domains in the chips. The emission frequency bands are estimated with a cyclotron resonance filter; the measurements show that the band width is of about that of the THz quantum cascade laser. By using long voltage pulses the chip heating above 100 K is achieved without substantial change in emission power. We speculate that the emission is super luminescence (amplification) of whispering gallery modes in the chips as a result of inverted Wannier-Stark level transitions under bias. The results are the first world demonstration of THz stimulated emission in a simple superlattice within region of positive DC differential conductivity; they give strong impetus for development of THz and higher frequency sources based on such simple superlattices; the sources should well compete with the THz quantum cascade lasers in particular at elevated temperatures.

New intraband semiconductor lasers—Wannier–Stark lasers—based on simple GaAs (150 A, quantum well)/GaAlAs (19 A with an aluminum fraction of 12%, barrier) superlattices have been demonstrated. The amplification mechanism in these lasers is based on population inversion between the ground Wannier–Stark level in the superlattice quantum wells and the weakly populated upper Wannier–Stark level in the wells two, three, or four periods down in the applied potential. Multiple regions of intense stimulated microwave emission near voltages of 8, 13, and 20 V (i.e., in the vicinity of resonances between these Wannier–Stark levels of the superlattice) have been discovered in the laser chips. The stimulated emission emerges in the circuit formed by the chip and its wiring. The emission from one of the chips at a temperature of up to 150 K (near 20 V applied to the chip) occurs at a frequency of about 7.3 GHz and has an estimated power of up to 1 W. It has been shown that the negative conductivity responsible for the emission still persists at 300 K but the emission is unseen owing to high losses in the circuit at this temperature. The superlattice wafer has been grown by metalorganic chemical vapor deposition. It consists of 1000 periods and a stop layer, to produce a metal–superlattice–metal terahertz resonator. Terahertz radiation has not been observed owing to a low amplification, as compared to losses in the resonator. According to the performed experiments, calculations, and discussions, such superlattices as radiation sources in gigahertz, terahertz, and higher frequency ranges could compete with quantum cascade lasers under appropriate optimization of their parameters.

Using a double-layer Cd x Hg 1− x Te structure, we demonstrate stimulated emission at two wavelengths simultaneously, around 2 μm and around 3 μm under optical excitation by a pulsed Nd:YAG laser at temperatures T =77–150 K. Emission spectra of the structure for various temperatures are presented.

Emissions at 2.6 – 2.8 THz are observed from liquid helium cooled disk chips with metal - superlattice - metal cavities made of two low n type doped wafers with weak barrier GaAs-GaAlAs superlattice of 1000 periods. The emissions are at 8.6 – 18.8 Volts within region of rising chip current (at positive chip differential conductivity) that guarantees absence of inhomogeneous electric field domains. At 2.6 – 2.7 THz the emission tunable by 8 – 10 Volts voltage change is higher than the Bloch oscillations frequency; while at 2.8 THz at 12 – 18 Volts it is lower than ω B , The THz frequency bands are measured with a cyclotron resonance filter; the band width is of about that of the THz quantum cascade laser. By using long voltage pulses the chip heating above 100 K is achieved without substantial change in chip THz emission power. We speculate that the emission is super luminescence (amplification) of whispering gallery modes in the chips as a result of inverted Wannier-Stark level transitions under bias. The results advocate development of THz and higher frequency sources based on such simple superlattices; the sources should well compete with the THz quantum cascade lasers in particular at elevated temperatures.

Dual-wavelength stimulated emission from a double-layer CdxHg1 − xTe heterostructure optically pumped by a pulsed Nd:YAG laser at temperatures T = 77–150 K is reported. The emission spectral lines have been observed at wavelengths λ1 ∼ 2 μm and λ2 ∼ 3 μm. Emission spectra recorded at different temperatures are presented.

We report stimulated near-IR emission in optically pumped InGaAs/AlGaInAs heterostructures and stimulated- emission wavelength switching from 1.9 to 1.5 and then to 1.2 μm with increasing optical pump intensity. The wavelength switching behaviour of the heterostructures depends on their geometry (band-gap profile) and the competition between stimulated emissions at different frequencies in different parts of the system.

The experimental observation of stimulated radiation of optically pumped CdxHg1 − x Te-based heterostructures in the wavelength range of 1.4–4.5 μm is reported. In the experiments, graded-gap Cd xHg1 − x Te samples grown on GaAs and Si substrates by molecular beam epitaxy were used. Superluminescence of such structures was observed at 77–300 K under the pulsed pumping of the samples by a Nd:YAG laser at a wavelength of 1.064 μm. At room temperature, stimulated radiation was observed at wavelengths of 1.4–1.7 μm. The obtained experimental data are the first results on the observation of stimulated radiation from graded-gap Cd x Hg1 − x Te structures on Si and GaAs substrates at these wavelengths at room temperature.

The experimental data on observation of spontaneous and stimulated emission from thin epitaxial CdxHg1−x Te films optically pumped by Nd: YAG laser radiation are reported. A simple theoretical model is suggested to describe the initiation of population inversion under these conditions. The parameters realized under the experimental conditions are theoretically estimated.

The properties of Mn-doped GaAs layers grown by laser deposition were investigated with measurements of Hall effect and magneto-optical Kerr effect (MOKE). The electrical and magnetic parameters of the layers were defined by growth temperature and quantity of sputtered Mn. It was shown that room-temperature ferromagnetism is revealed by MOKE and, after ruby laser 25 ns pulse annealing, by Hall effect measurements.

A photomagnetization effect is observed for a (Tm,Bi)3(Fe,Ga)5O12 garnet film at T = 300 K due to the restructurization of its multidomain structure. Photomagnetization (ΔM) emerges under the action of circularly polarized laser radiation in the spectral range of 450–600 nm at lasing power P < 600 kW/cm2 and pulse duration τi ∼ 7ns. The dependences of ΔM are measured on the polarization of light and magnetic field, the latter being perpendicular to the surface of the film. The maximum value of ΔM is observed for the circular polarization of light without a magnetic field. Moreover, ΔM changes sign with as the circular polarization changes sign and is zero for linear polarization.

A method for diagnostics of the interaction of electron states in multilayer heterostructures in a dc electric field is suggested. The method is based on measurements of the resonance response of the harmonic amplitude of the current in a heterostructure to modulated laser radiation. The method is used for studying tunneling between the Wannier-Stark levels in the superlattice with strongly coupled quantum wells.

Stimulated emission of radiation from CdxHg1−xTe samples pumped by a Nd:YAG laser at temperature T≈77 K is obtained. Both spontaneous and stimulated emission is observed for the wavelengths λ in the range 3300–3600 nm. Experimental emission spectra are presented. The special features of the spectra and the possible applications of the structures are discussed.

The crystal structure and transport properties of epitaxial c-oriented YBa2Cu3O7−x films are investigated for high-T c layer thicknesses from 5 to 300 nm. The films were prepared by laser deposition. Films less than 30 nm thick become predominantly single-domain in the direction of the c axis. As the thickness decreases, the orthorhombicity parameter of the YBaCuO lattice decreases, which correlates with the critical temperature degradation observed in films less than 9 nm thick. The obtained thickness dependence of the effective microwave surface resistance of a YBaCuO film agrees well with the computational result obtained in the framework of local electrodynamics for samples with a constant microwave conductance.

The results are reported on the observation of the induced emission from CdxHg1−x Te samples optically pumped by a pulsed Nd:YAG laser at temperatures T

The experimental results of the film parameter evaluation based on recording detective coil signal produced by the film in external or remanent magnetic field subject to a laser pulse at any specific spot in the film are presented. The mechanisms of the film response to the laser irradiation based on Bean-like model for the inhomogeneous superconductive film are discussed. >

The main requirements for the MCT (Cd x Hg 1−x Te) structures optimization for increase of the stimulated emission wavelength under optical pumping are discussed. The stimulated emission at wavelengths 2–2.5 µm at room temperature from optimized MCT structures is observed experimentally. The obtained experimental data are the first observation of stimulated emission from the MCT structures at these wavelengths at room temperature.

The experimental observation of stimulated radiation of optically pumped Cd{sub x}Hg{sub 1-x} Te-based heterostructures in the wavelength range of 1.4-4.5 {mu}m is reported. In the experiments, graded-gap Cd {sub x}Hg{sub 1-x} Te samples grown on GaAs and Si substrates by molecular beam epitaxy were used. Superluminescence of such structures was observed at 77-300 K under the pulsed pumping of the samples by a Nd:YAG laser at a wavelength of 1.064 {mu}m. At room temperature, stimulated radiation was observed at wavelengths of 1.4-1.7 {mu}m. The obtained experimental data are the first results on the observation of stimulated radiation from graded-gap Cd {sub x} Hg{sub 1-x} Te structures on Si and GaAs substrates at these wavelengths at room temperature.

Experiments on the nonequilibrium resistive response of YBa2Cu3O7−x superconducting thin films to laser radiation are reported. Separate fast and slow components of the photoresponse were observed. Photoresponses to a sequence of laser pulses of various amplitudes were investigated. A memory effect has been observed, revealing a correlation between the photoresponse pulse amplitude and the preceding laser pulse amplitude. A theoretical model of the memory effect is suggested.

The experimental observation of stimulated radiation of optically pumped CdxHg1-xTe structures in the wavelength range of 1.4 - 4.5 mum is reported. In the experiments, graded-gap CdxHg1-xTe samples grown on GaAs and Si substrates by molecular beam epitaxy were used. Superluminescence of such structures was observed at 77 - 300 K under the pulsed pumping of the samples by a Nd:YAG laser at a wavelength of 1.064 mum. At room temperature, stimulated radiation was observed at wavelength of 1.4 - 1.7 mum. The obtained experimental data are the first results on the observation of stimulated radiation from graded-gap CdxHg1-xTe structures on Si and GaAs substrates at these wavelengths at room temperature.

grown on GaAs andKeywords : Superlum inescence, stimulated emission, heterostructures, optical pumping, narrow gap semiconductorsThere has been increasing interest in developing semiconductor lasers that operate in the 1 .5 -- .tm wavelength range and,jim, 8÷12 pin). intraband cascade lasers andinterband lasers using type-IT heterostructures (e.g TnAs/TnGaSb/TnAs system) (see, e.g., [1 ,2]) are the main candidates forHeterostructures based on CdHgjTe system where direct radiative transitions are allowed, could be also a good candidatefabrication technology of CdHgjTe structures, caused by a need for development of advanced infrared detectors and

It is shown that active systems based on inter-subband transitions of hot holes could provide tunable FIR sources. Liquid helium cooled Ge is the most promising system—and some results are quoted—while for higher temperatures (with higher E and H fields) Si is the most likely material.

Basic principles for arranging population inversion and stimulated emission in hot hole systems at low temperature are discussed. Recent experimental results on observation of emissions from intersubband lasers, CR NEMAG's and CR lasers made from p-Ge are given.

We briefly review the studies devoted to development and applications of terahertz and multiterahertz quantum cascade lasers on intraband transitions in quantum wells of semiconductor heterostructures, which appeared in the last 5–7 years. Such lasers developed recently for the frequency band 3.5-70 THz find more and more applications in spectroscopy, communication, etc. We describe the first experiments performed at the Institute of the Physics of Microstructures of the Russian Academy of Sciences on studying the parameters of multiterahertz cascade lasers provided by our European colleagues.

An investigation was made of the spectral composition of the radiation emitted by longwavelength infrared lasers made of p-type Ge. Single-frequency emission was achieved.