Polarization bistability and resultant spin rings in semiconductor microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on spin dependent Gross-Pitaevskii equations provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.Comment: 5 pages, 3 figure

Ultrafast Depopulation of a Quantum Dot by LA-phonon-assisted Stimulated Emission

We demonstrate ultrafast \emph{incoherent} depopulation of a quantum dot from above to below the transparency point using LA-phonon-assisted emission stimulated by a red-shifted laser pulse. The QD is turned from a weakly vibronic system into a strongly vibronic one by laser driving which enables the phonon-assisted relaxation between the excitonic components of two dressed states. The depopulation is achieved within a laser pulse-width-limited time of 20~ps and exhibits a broad tuning range of a few meV. Our experimental results are well reproduced by path-integral calculations

Dynamic vibronic coupling in InGaAs quantum dots

The electron-phonon coupling in self-assembled InGaAs quantum dots is relatively weak at low light intensities, which means that the zero-phonon line in emission is strong compared to the phonon sideband. However, the coupling to acoustic phonons can be dynamically enhanced in the presence of an intense optical pulse tuned within the phonon sideband. Recent experiments have shown that this dynamic vibronic coupling can enable population inversion to be achieved when pumping with a blue-shifted laser and for rapid de-excitation of an inverted state with red detuning. In this paper we confirm the incoherent nature of the phonon-assisted pumping process and explore the temperature dependence of the mechanism. We also show that a combination of blue- and red-shifted pulses can create and destroy an exciton within a timescale ∼ 20 ps determined by the pulse duration and ultimately limited by the phonon thermalisation time

Phonon-Assisted Population Inversion of a Single InGaAs/GaAs Quantum Dot by Pulsed Laser Excitation

We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations

A proposed method for determining shrub utilization using (LA/LS) imagery

Utilization of plant above ground biomass has continued to be a critical yet difficult assessment in rangeland monitoring. Shrub size and woody structure further compound the measurement of shrub biomass utilization. This study was designed to determine the potential utility of low altitude/large scale (LA/LS) imagery in assessing shrub utilization. A near monoculture of Ceriotoides lanata (Pursh) J.T. Howell (winterfat) located in the western desert shrubland of Utah was used to evaluate this technique. Four, 3.1 by 3.1 m plots were identified and the shrubs within the plots were defoliated by hand-picking at about 10% intervals with imagery of the plots obtained between pickings. Imagery was obtained using a radio controlled airplane (drone) fitted with a 35 mm camera. Images were evaluated using image processing software and the resulting reflectance data correlated with defoliation percentages (weight basis) for each plot. Reflectance data from images correlated highly with defoliation percentages (r2 > 0.9). This technique of using LA/LS imagery shows promise for a quick and accurate tool in assessing utilization of shrubs.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Patients with skin smear positive leprosy in Bangladesh are the main risk factor for leprosy development: 21-year follow-up in the household contact study (COCOA).

BackgroundLeprosy transmission is ongoing; globally and within Bangladesh. Household contacts of leprosy cases are at increased risk of leprosy development. Identification of household contacts at highest risk would optimize this process.MethodsThe temporal pattern of new case presentation amongst household contacts was documented in the COCOA (Contact Cohort Analysis) study. The COCOA study actively examined household contacts of confirmed leprosy index cases identified in 1995, and 2000-2014, to provide evidence for timings of contact examination policies. Data was available on 9527 index cases and 38303 household contacts. 666 household contacts were diagnosed with leprosy throughout the follow-up (maximum follow-up of 21 years). Risk factors for leprosy development within the data analysed, were identified using Cox proportional hazard regression.FindingsThe dominant risk factor for household contacts developing leprosy was having a highly skin smear positive index case in the household. As the grading of initial slit skin smear of the index case increased from negative to high positive (4-6), the hazard of their associated household contacts developing leprosy increases by 3.14 times (pInterpretationWe found a dominance of a single variable predicting risk for leprosy transmission-skin smear positive index cases. A small number of cases are maintaining transmission in the household setting. Focus should be performing contact examinations on these households and detecting new skin smear positive index cases. Conducting slit-skin smears on new cases is needed for predicting risk; such services need supporting. If skin smear positive cases are sustaining leprosy infection within the household setting, the administration of single-dose rifampicin (SDR) to household contacts as the sole intervention in Bangladesh will not be effective