Room-temperature polariton lasing in semiconductor microcavities

We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 microJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.     

Circularly polarized light emission from semiconductor planar chiral nanostructures

We demonstrate circularly polarized light emission from InAs quantum dots embedded in the waveguide region of a GaAs-based chiral nanostructure. The observed phenomenon originates due to a strong imbalance between left- and right-circularly polarized components of the vacuum field and results in a degree of polarization as high as 26% at room temperature. A strong circular anisotropy of the vacuum field modes inside the chiral nanostructure is visualized using numerical simulation. The results of the simulation agree well with experimental results.     

Hot electron light-emitting and lasing semiconductor heterostructures--type 1

A new light-emitting device has been proposed based on the incorporation of a GaAs quantum well on the n-side, and in the depletion region, of a Ga_1-xAl_xAs p-n junction, where the bias is applied parallel to the layers. Light is emitted when electrons and holes on the n- and p-side of the structure, respectively, heated by the applied longitudinal electric field, transfer to the quantum well, by resonant tunnelling and thermionic emission (electrons) and diffusion (holes), where they recombine radiatively. The intensity of the light emitted is independent of the polarity of the applied bias. A demonstration of the device is presented and it is shown that the quantum well needs to be in the depletion region for light emission to occur. The device is modelled theoretically by solving the Schrödinger's and Poisson's equations self-consistently by including the carrier dynamics for hot electrons and holes.     

Excitonic waveguiding and lasing in wide bandgap semiconductor

New type of structures for optoelectronics, we refer to as excitonic waveguides, are proposed and realized. Oppositely to conventional waveguides and double-heterostructure lasers, no significant difference in the average refractive index between the cladding and the active layers is necessary, and these regions can be fabricated from the same matrix material (homojunction laser). In this approach: (i) the waveguiding effect has a resonant nature and appears on the low-energy side of the strong exciton absorption peak in agreement with the Kramers-Kronig transformation; (ii) the absorption peak is induced by nanoscale island-like insertions of narrow-gap material in a wide bandgap matrix (quantum dots), preventing free-carrier screening of excitons and, simultaneously, allowing lasing resonant to the spectral range of the enhanced refractive index. Fiz. Tverd. Tela (St. Petersburg) 40, 843–845 (May 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Comparative analysis of the effects of internal lasing oscillation and external light injection on semiconductor optical amplifier performance

One of the key differences of a semiconductor optical amplifier (SOA) with internal lasing oscillation (ILO) from a SOA with external light injection (ELI) lies in a carrier-sharing mechanism. Since the internal lasing mode shares the same pool of carriers with the signals, the carriers (or photons) withdrawn from the circulating laser mode speed up the gain recovery. On the other hand, the external light injected into the SOA shortens the carrier recovery time through optical pumping without any carrier sharing involved. To find out a better scheme, we have made a comparative investigation on the effects of the ILO and ELI on the SOA performance. It turns out by way of simulation that the ELI scheme provides faster gain recovery, shorter carrier lifetime, and higher saturation power when the external injection power is higher than the internal lasing power. The performance enhancement is not so pronounced with the carrier-sharing mechanism, as the internal lasing mode itself gives rise to severe longitudinal spatial hole burning (LSHB). Nevertheless, the ILO scheme is preferable for linear-amplification applications. We also examine the use of the ELI for low-crosstalk optical amplifiers. It is found that the ELI scheme does not bring in a very strong resonance peak in the crosstalk, which appears in a SOA with ILO due to relaxation oscillations of the lasing mode. In comparison to the ILO in SOAs, the ELI into SOAs is likely to leave more optical gain for multi-channel amplification without any sacrifice on the crosstalk.     

Collective spontaneous emission of dye molecules and lasing

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×10¹⁸ cm^?3, the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.     

Thermal instability of a semiconductor in a lasing beam

The thermal balance is considered in an intrinsic semiconductor in the presence of a laser beam with a photon energy less than the width of the forbidden band, as a result of which absorption by free carriers plays the principal role. It is shown that a radiation power threshold exists above which the stationary temperature distribution is impossible. For typical values of the parameters the threshold power is 1 kW, and the time required for instability to develop is 10^–3–1 sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 1, pp. 33–37, January, 1972.The author is indebted to V. L. Bonch-Bruevich, Yu. V. Gulyaev, I. P. Zvyagin, P. E. Zil'berman and A. G. Mironov for discussing the work.     

Self-detection of lasing characteristics for semiconductor ring laser diodes

A novel method of measurement of lasing characteristics for a ring laser diode is proposed without branching of the optical lasing power. The lasing power and the linewidth as a function of the injection current have been measured by detecting the RF power by the terminal voltage change of a ring LD. The linewidth is estimated to be 55 kHz atl=1.75l _th.     

Theory of light scattering from semiconductor quantum dots: Excitation frequency dependent emission dynamics

We present a microscopic model for the dynamic scattering and emission spectrum of a semiconductor quantum dot, after coherent optical excitation. We investigate the spectral properties and the emission dynamics of the different scattering and emission contributions considering a V-type semiconductor quantum dot model under resonant conditions and include the coupling to LO-phonons via higher order Born approximations. This theory helps identifying the different contributions to the spectrum via time resolved calculations.     

Plasmonic leaky‐mode lasing in active semiconductor nanowires

Leaky modes are below‐cutoff waveguide modes that lose part of their energy to the continuum of radiation modes during propagation. In photonic nanowire lasers, leaky modes have to compete with almost lossless above‐cutoff modes and are therefore usually prevented from crossing the lasing threshold. The situation is drastically different in plasmonic nanowire systems where the above‐cutoff plasmonic modes are very lossy because of their strong confinement to the metal surface. Due to gain guiding, the threshold gain of the hybrid electric leaky mode does not increase strongly with reduced wire diameter and stays below that of all other modes, making it possible to observe leaky‐mode lasing. Plasmonic ZnO nanowire lasers operating in the gain‐guided regime could be used as coherent sources of surface plasmon polaritons at the nanoscale or as surface plasmon emitting diodes with an emission angle that depends on the nanowire diameter and the color of the surface plasmon polariton.

     

Multiwavelength fiber ring lasing by use of a semiconductor optical amplifier

A multiwavelength fiber ring laser obtained by use of a semiconductor optical amplifier (SOA) with a simple laser cavity configuration is reported. A Fabry-Perot filter was used in the fiber laser ring cavity to achieve more than 50 simultaneous wavelength lasing oscillations with a frequency separation of 50 GHz. The resulting stable broadband multiwavelength lasing operation was attributed to broadband and flat gain of the SOA, which has a gain flatness of 0.8 dB for more than 20 nm. The laser has a total output power of -3 dBm and a signal-to-spontaneous-noise ratio of 30 dB.     

Quantum logics and chemical kinetics

A statistical theory of chemical kinetics is presented based on the quantum logical concept of chemical observables. The apparatus of Boolean algebra $\text{B}$ is applied for the construction of appropriate composition polynomials referring to any stipulated arrangement of the atomic constituents. A physically motivated probability measure μ(F) is introduced on the field $\text{B}$ of chemical observables, which considers the occurrence of the yes response of a given F ? $\text{B}$. The equations for the time evolution of the species density operators and the master equations for the corresponding number densities are derived. The general treatment is applied to a superposition of elementary substitution reactions (AB)_α + C ? (AC)_β + B. The expressions for the reaction rate coefficients are established.     

Phase-conjugate backward stimulated emission from a two-photon-pumped lasing medium

Optical phase conjugation of the two-photon-pumped frequency upconversion backward stimulated emission of a new dye solution has been demonstrated. When the 1064-nm pump intensity reaches a certain threshold value, a highly directional and phase-conjugate backward stimulated emission at ~616-nm wavelength can be observed. After backward passage through an aberration plate placed in the input pump beam path, the introduced aberration influence (1.6-1.8 mrad) can be entirely compensated by backward stimulated emission with a final beam divergence of only 0.23 mrad. The net conversion efficiency from the absorbed IR pump energy to the backward visible stimulated emission energy can reach 10%.     

THz emission from semiconductor surfaces

We provide a review of experimental and theoretical work on electromagnetic terahertz pulse emission from semiconductor surfaces excited by femtosecond laser radiation. The main terahertz emission mechanisms are analysed. The terahertz emission from InAs and Ge is explained by the photo-Dember effect and electric field induced optical rectification. Electronic band structure and carrier scattering mechanisms are investigated by means of terahertz emission and absorption spectroscopy in InAs, InSb and Ge. To cite this article: V.L. Malevich et al., C. R. Physique 9 (2008).     

Quantum fluctuations in atomistic semiconductor devices

Atomistic Green function simulations of model 25 nm×25 nm Si MOSFETs predict strong fluctuation effects derived from mode fluctuations in the quantum transport through the inhomogeneous 2DEG channel caused by the spatial distribution of non-self-averaged discrete dopants.