Coherent dynamics of the localized vibrational modes of hydrogen in CaF2

We report the observation of giant quantum coherence effects in the localized modes of ionized hydrogen in synthetic fluorite. Infrared free induction decay experiments on the substitutional H- center show dramatic modulations at negative delay times due to interference between multiple vibrational levels. Spectrally resolving the degenerate four wave mixing signal allows unambiguous assignments of the participating vibrational states. The dependence of the signal intensity upon the delay path between the exciting free electron laser pulses can be accounted for in terms of the resonant third order polarization with a common dephasing time for the excited states.     

Resonant Raman scattering from screened longitudinal optical phonons in EuTe

Forbidden resonant Raman scattering from screened longitudinal optical, LO, phonons has been observed in the back-reflection geometry from n-type EuTe at 2°K. The Raman shift increased with increasing excitation frequency but was always between the LO and TO phonon frequencies. This effect is explained in terms of a varying ‘effective’ carrier concentration as a function of laser penetration depth through the surface depletion layer in the situation of large phonon wave vector. Conduction band and lattice parameters have been calculated from infrared Reststrahlen and plasma edge measurements.     

Tunable far-infrared generation by difference frequency mixing in InSb

Far-infrared radiation tunable over the range 85–105 cm^-1 and at power levels of up to 10 μW has been generated by difference frequency mixing in InSb. The infra-red radiations which are mixed are a 10.6 μm TEA-CO₂ laser line and the tunable Stokes radiation produced from it by spin-flip Raman-laser action, again in an InSb sample. It is argued that careful choice of the free-carrier concentrations in the crystals used for (a) the Stokes generation and (b) the mixing, or the application of an electric field across the mixing sample, should considerably improve the far-infrared power levels.     

Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.