The principle objective of this project is the development of new types of sensitive, selective, real-time gas sensors based on continuous wave and pulsed quantum cascade lasers for various chemical sensing applications ranging from medical diagnostics to monitoring spacecraft air quality. Tunable laser absorption spectroscopy in the mid-infrared spectral region is a sensitive analytical technique for trace gas quantification. Nitric Oxide (NO) detection from exhaled breath is of particular interest for the diagnosis of lower airways inflammation associated with a number of lung diseases and illnesses. Investigation focuses upon the feasibility of detecting NO in expired human breath as a potential non-invasive medical diagnostic tool. A gas analyzer based on a CW mid-infrared quantum cascade laser operating at ~ 5.2 mm and off-axis integrated cavity output spectroscopy (ICOS) has been developed to measure NO concentrations in human breath. A compact sample cell, 5.3 cm in length with a volume of < 80 cm 3, suitable for on-line and off-line measurements during a single breath cycle, has been designed and evaluated. A noiseequivalent (SNR = 1) sensitivity of 10 parts-per-billion by volume (ppbv) of NO was achieved. The combination of offaxis integrated cavity output spectroscopy with wavelength modulation resulted in a 2 ppbv noise-equivalent sensitivity

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