Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was operated at liquid nitrogen temperature near lambda = 5.2 microns. In the first configuration, a 100 m optical path length multi-pass cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb when using CES. The two techniques are compared, and potential future developments are discussed.

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A surface passivation method for normalGaAs , with possible extensions to normalInGaAs and normalGaSb , is proposed. For normalGaAs , a correlation between recent device work (on solar cells, field effect transistors, MOS devices, and photodiodes) and the experimental Ga‐As‐O phase diagram provides strong evidence of the role of elemental surface or interface arsenic or arsenic oxide in device performance degradation. On this basis, a hydrogenation/nitridization passivation technique is proposed. The reactions to remove surface As and As2O3 areAs2O3+12H→3H2O↑+2AsH3↑ normalAs+3H→AsH3↑The surfaces may be plasma coated in the same chamber with a wide bandgap nitride (e.g., normalGaN ) for passivation and to tie up any elemental Ga. The hydrogenation and nitridization steps may be simultaneous if an ammonia plasma is used. A final Si3N4 layer for long‐term surface protection is recommended. Recent experimental data on normalGaAs surface treatments support this passivation mechanism. The extension to normalInGaAs (for long wavelength optical detectors) is by thermochemical calculations supported by recent parallel measurements of the In‐Ga‐As‐O phase diagram. Note the conductive indium oxide must also be removed, as by the reactionIn2O3+4H→In2O↑+2H2O↑

We report the first application of pulsed, near-room-temperature quantum cascade laser technology to the continuous detection of biogenic CO production rates above viable cultures of vascular smooth muscle cells. A computer-controlled sequence of measurements over a 9-h period was obtained, resulting in a minimum detectable CO production of 20 ppb in a 1-m optical path above a standard cell-culture flask. Data-processing procedures for real-time monitoring of both biogenic and ambient atmospheric CO concentrations are described.

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