Electron-spin beat susceptibility of excitons in semiconductor quantum wells

Recent time-resolved differential transmission and Faraday rotation measurements of long-lived electron spin coherence in quantum wells displayed intriguing parametric dependencies. For their understanding we formulate a microscopic theory of the optical response of a gas of optically incoherent excitons whose constituent electrons retain spin coherence, under a weak magnetic field applied in the quantum well's plane. We define a spin beat susceptibility and evaluate it in linear order of the exciton density. Our results explain the many-body physics underlying the basic features observed in the experimental measurements

Relations between the SNO and the Super Kamiokande solar neutrino rates

By comparing the neutrino spectra measured by SNO and Super Kamiokande, we obtain inequalities between the ratios of observed rate to SSM rate for the two experiments. These inequalities apply to a possibly energy-dependent reduction of the SSM flux and to the case of neutrino oscillations. We use them to examine the relationship between the two experiments expected for the MSW and ``Just-So" oscillation scenarios.Comment: 8 pages + 3 figures, REVTeX, uuencoded file created on a VMS syste

High-power 1.3 µm superluminescent diode

Superluminescent diodes with high output power (10 mW at 175 mA), wide spectral width (28 nm), low spectral modulation depth (<15%), wide frequency modulation bandwidth (570 MHz), and high single-mode fiber coupling efficiency (40%) are reported. The structure is based on a buried crescent laser structure with an antireflection coating and a "short-circuit" absorber to suppress lasing

Determining the Effects of Hydrothermal Alteration on the Sorption of Neptunium and Europium onto Bentonites

The Clay Mineral Society SWy-2 Na-montmorillonite clay was reacted for 90 days with 15 mM K+ at 200°C, the temperature/solution conditions of deep geologic repository near-field regions. X-ray diffraction of alteration products indicated that a minor amount of interstratification occurred in the clay. Hydrothermally altered samples sorbed stable Eu and 237Np almost as effectively as the unaltered clay. Average Kd values were 1.79 × 102 kg/L – 2.37 × 105 kg/L (Euonto altered clay), 3.05 × 102 kg/L – 1.54 × 106 kg/L (237Np onto altered clay), 3.55 × 104 kg/L – 1.30 × 106 kg/L (Euonto unaltered clay), and 1.04 × 103 kg/L (237Np onto unaltered clay). Speciation models indicated that Eu(III) and Np(V) complexation was influenced by the presence of chloride and hydroxide, but the largest observed impact on Eu and Np(V) sorption was solution pH which altered the affinity of Eu and Np(V) for the mineral surface