Vibrational energy transfer in hydrogen liquid and its isotopes

The transfer of vibrational energy (V-V) from H₂ to isotopic impurities (HD or D₂) has been studied in the liquid state, between 15 and 30 K. The subsequent relaxation (V-T) of the excited impurity by the H₂ liquid host has also been measured and contrasted with the vibrational relaxation behaviour of pure H₂ and D₂ liquids. The isothermal density dependence of both V-V and V-T transfer has been investigated in the fluid state at 30 K. High density relaxation rates are also compared to our data in the pure gases and to other available gas phase results. Measurements in the solid, near the triple point temperature, are equally reported for each process studied.     

Electronic structure of GaSbAlSb superlattices

We present optical absorption experiments performed at low temperature in very high quality GaSbAlSb superlattices grown by MBE. The absorption spectra exhibit pronounced exciton peaks separated by absorption plateaus. The data are interpreted within an effective mass theory, taking into account the effect of strains induced by the 0.65 % lattice mismatch of the hosts. From the number of observed transitions, we can determine quite accurately the band offsets in this system. The crossover of the quantized states originating from the Λ and L minima of the GaSb conduction band is also discussed.     

Parametric generation of twin photons in vertical triple microcavities

We report the realization of a monolithic vertical-cavity, surface emitting micro-optical parametric conversion nanostructure, triply resonant with the parametric frequencies, allowing parametric oscillation with ultra-low pump power threshold. The photonic phase-space naturally provides triple resonance for the parametric frequencies, together with built-in cavity phase-matching for the pump wave at normal incidence. Parametric oscillation is observed in both the strong and weak exciton–photon coupling regime, allowing a high operating temperature. Signal and idler beams can be collected at 0° or at finite angles. The OPO threshold is low enough to envisage the realization of an all-semiconductor electrically-pumped micro-parametric oscillator. To cite this article: C. Diederichs et al., C. R. Physique 8 (2007).     

Huang–Rhys side-bands in the emission line of a single InAs quantum dot

We report the first direct observation of Huang–Rhys side-bands in the photoluminescence spectrum of a single InAs/GaAs quantum dot (QD). At low temperature (10 K) the single QD spectrum has a quasi-Lorentzian profile. At higher temperatures, we observe a strong deviation from a Lorentzian profile with the appearance of asymmetric side-bands which become symmetric above 70 K. We obtain an excellent agreement with theoretical calculations done in the framework of the Huang–Rhys formalism. We conclude that the zero-phonon linewidth is the relevant parameter for the observation of the low-energy acoustic phonon side-bands.     

Coherent response of a semiconductor microcavity in the strong coupling regime

We have studied the coherent dynamics of a semiconductor microcavity by means of interferometric correlation measurements with subpicosecond time resolution in a backscattering geometry. Evidence is brought of the resolution of a homogeneous polariton line in an inhomogeneously broadened exciton system. Surprisingly, photon-like polaritons exhibit an inhomogeneous dephasing. Moreover, we observe an unexpected stationary coherence up to 8 ps for the lower polariton branch close to resonance. All these experimental results are well reproduced within the framework of a linear dispersion theory assuming a coherent superposition of the reflectivity and resonant Rayleigh scattering signals with a well-defined relative phase.     

Laser induced two-photon decay in Pr3+:LaAlO3

A laser induced two-photon decay has been observed between the ³P₀ and ³F₂ levels of trivalent praseodymium in LaAlO₃. The differential transition cross section was found to be dσ/dΩ = 1.1 × 10^-27 cm².     

Vibrational relaxation of compressed nD2 fluid

Experimental observations of the vibrational population relaxation time of ⁿD₂ fluid under pressures of up to 500 atm in the 25–85 K range are presented and described in terms of a semi-classical model for energy transfer in liquids. For comparison with the parameters of this model, a classical equivalent potential for quantum systems is derived from the “real” intermolecular potential.     

Transfer dynamics from an interface type-II heavy-hole exciton to a type-I light-hole exciton in a ZnSe/(Zn,Mn) Se heterostructure

Il Nuovo Cimento D - Resonant photoluminescence and excitation spectroscopy and time-resolved photoluminescence are performed on a 50 Å thick ZnSe/(Zn, Mn) Se strained quantum well. From these...