h S T R A C TWe report the first ab initio quantum mechanical investigation of the structure of the E', center in amorphous SiOz (a-SiOz). Our calculations suggest that the unpaired electron is shared by only two Si atoms, irrespective of the Si cluster size.

The Geostationary Lightning Mapper (GLM) instrument onboard the GOES 16 and 17 satellites can be used to detect bolides in the atmosphere. This capacity is unique because GLM provides semi-global, continuous coverage and releases its measurements publicly. Here, six filters are developed that are aggregated into an automatic algorithm to extract bolide signatures from the GLM level 2 data product. The filters exploit unique bolide characteristics to distinguish bolide signatures from lightning and other noise. Typical lightning and bolide signatures are introduced and the filter functions are presented. The filter performance is assessed on 144845 GLM L2 files (equivalent to 34 days-worth of data) and the algorithm selected 2252 filtered files (corresponding to a pass rate of 1.44%) with bolide-similar signatures. The challenge of identifying frequent but small, decimeter-sized bolide signatures is discussed as GLM reaches its resolution limit for these meteors. The effectiveness of the algorithm is demonstrated by its ability to extract confirmed and new bolide discoveries. We provide discovery numbers for November 2018 when seven likely bolides were discovered of which four are confirmed by secondary observations. The Cuban meteor on Feb 1st 2019 serves as an additional example to demonstrate the algorithms capability and the first light curve as well as correct ground track was available within 8.5 hours based on GLM data for this event. The combination of the automatic bolide extraction algorithm with GLM can provide a wealth of new measurements of bolides in Earth’s atmosphere to enhance the study of asteroids and meteors.

We describe the photoluminescence spectroscopy (PL) and Fourier transform infrared absorbance spectroscopy characterization of a large set of InAs/GaSb type-II strained layer superlattice (SLS) samples. The samples are designed to probe the effect of GaSb layer thickness on the optical properties of the SLS, while the InAs-layer thickness is held fixed. As the GaSb layer thickness is increased, we observe a spectral blue shift of the PL peaks that is accompanied by an increase in intensity, narrower linewidths, and a large reduction in the temperature sensitivity of the luminescence. These effects occur despite a significant reduction in the electron-hole wave function overlap as the GaSb layer thickness is increased. In addition, we compare the results of empirical pseudopotential model (EPM) calculations to the observed blueshift of the primary band gap. The EPM calculations are found to be in very good agreement with the observed data.

We report on optically pumped semiconductor lasers emitting near 3.8 μm that exhibit high power and low output divergence. The lasers incorporate multiple InAs/InGaSb/InAs type-II wells imbedded in an InGaAsSb waveguide that is designed to absorb the pump emission. When operated at 85 K, 0.25 mm×2.5 mm broad area devices produce >5 W of peak power under long pulse conditions. Moreover, these extremely bright devices exhibit a fast axis divergence of only ∼15° full width at half maximum (FWHM), coupled with a slow axis divergence of ∼6° FWHM. The first is due to the reduced optical confinement in the transverse direction, while the latter is attributed to the suppression of filament formation, which is another beneficial consequence of the low optical confinement.