High-resolution Fourier-transform photoluminescence spectroscopy combined with the resonant photoexcitation technique was used to study in detail the Zeeman eff'ect on excitons bound to the neutral donors in high purity epitaxial GaAs. The neutral donor g-factor depends on the magnetic-field intensity and orientation in agreement with the predictions of the five-level k p theory. The neutral-donor excited-state energies measured in a range of magnetic field from 0 to l2 T are in an excellent agreement with appropriately scaled calculations for the hydrogen atom. The correspondence between transitions having the same initial state but having as a final state either the nuetral-donor ground state (principal transitions) or a neutral donor excited state (two electron satellites) was established using resonant excitation and was verified by the angular dependences of the peak energies. Linear and circular polarizations of the 2p, 2po, and 2p+ two-electron satellites are consistent with the assignment of zero angular momentum to the ground state of the donor-bound exciton and we show that the transition energies for these components can be calculated with a 0.03-meV accuracy over the range from 0 to 12 T.
Standoff detection, identification and quantification of chemical agents are fundamental needs in several fields of applications. Additional required sensor characteristics include high sensitivity, low false alarms and high-speed (ideally real-time) operation, all in a compact and robust package. The thermal infrared portion of the electromagnetic spectrum has been utilized to implement such chemical sensors, either with spectrometers (with none or moderate imaging capability) or with imagers (with moderate spectral capability). Only with the recent emergence of high-speed, large format infrared imaging arrays, has it been possible to design chemical sensors offering uncompromising performance in the spectral, spatial, as well as the temporal domain.Telops has developed an innovative instrument that can not only provide an early warning for chemical agents and toxic chemicals, but also one that provides a "Chemical Map" in the field of view. To provide to best field imaging spectroscopy instrument, Telops has developed the FIRST, Field-portable Imaging Radiometric Spectrometer Technology, instrument. This instrument is based on a modular design that includes: a high-performance infrared FPA and data acquisition electronics, onboard data processing electronics, a high-performance Fourier transform modulator, dual integrated radiometric calibration targets and a visible boresight camera. These modules, assembled together in an environmentally robust structure, used in combination with Telops' proven radiometric and spectral calibration algorithms make this instrument a world-class passive standoff detection system for chemical imaging. This paper presents chemical detection and identification results obtained with the FIRST sensor.
Standoff detection, identification and quantification of chemicals in the gaseous state are fundamental needs in several fields of applications. Sensor requirements derived from these applications include high sensitivity, low false alarms and real-time operation, all in a compact and robust package suitable for field use. The thermal infrared portion of the electromagnetic spectrum has been utilized to implement such chemical sensors, either with spectrometers (with no or moderate imaging capability) or with imagers (with moderate spectral capability). Only with the recent emergence of high-speed, large format infrared imaging arrays has it been possible to design chemical sensors offering uncompromising performance in the spectral, spatial, as well as the temporal domain. It is clear from analytical studies that the combined spatial and spectral information holds enormous promises on improving the current performance of passive detection, identification and quantification of chemical agents. This paper presents detection, identification and quantification algorithms developed for hyperspectral imagers operating in the thermal infrared. The effectiveness of these algorithms is illustrated using gaseous releases datacubes acquired using the Telops FIRST imaging spectrometer in the field.
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