Recent advances in the development of sensors based on infrared quantum cascade lasers for the detection of trace gas
species is reported. Several selected examples of applications in environmental and industrial process monitoring as well
as in medical diagnostics using quartz enhanced photoacoustic spectroscopy and laser absorption spectroscopy will be
described.
Exhaled nitric oxide (NO) is an important biomarker in asthma and other respiratory disorders. The optical performance of a NO/CO2 sensor employing integrated cavity output spectroscopy (ICOS) with a quantum cascade laser operating at 5.22 µm capable of real-time NO and CO2 measurements in a single breath cycle is reported. A NO noise-equivalent concentration of 0.4 ppb within a 1-sec integration time is achieved. The off-axis ICOS sensor performance is compared to a chemiluminescent NO analyzer and a nondispersive infrared (NDIR) CO2 absorption capnograph. Differences between the gas analyzers are assessed by the Bland-Altman method to estimate the expected variability between the gas sensors. The off-axis ICOS sensor measurements are in good agreement with the data acquired with the two commercial gas analyzers. This work demonstrates the performance characteristics and merits of mid-infrared spectroscopy for exhaled breath analysis.
Theoretical and experimental studies the features of parametric generation light in LiNbO3 with non-collinear phase matching from non-collinear angle i23, i.e. angle between pump wave vector and resonant signal wave vector, are presented. It was shown that at the small angle i23<0,3 degrees four nonlinear processes can simultaneously take place: these processes are non-collinear parametric conversion of the 1.0642 micrometers into the signal and an idler waves; second-harmonic generation of the signal; non- collinear difference-frequency mixing of the doubled signal and the idler; parametric conversion of the doubled signal into new pair: the signal and an idler waves. It is shown that the maximum efficiency of non-collinear OPO takes place for tangential phase-matching at (formula available in paper). Spectral broadening of the signal wave of LiNbO3 non-collinear OPO was studied. Theoretically it is shown that the spectral bandwidth of the signal wave depends on the divergence of the signal wave.
The development of a differential absorption lidar (DIAL) system in the mid-IR region for the detection and monitoring of light hydrocarbons is presented. Two lithium niobate optical parametric oscillators provided the signal and reference wavelengths. With the aid of a topographical target the system detected 0,4 ppm of propane and 0.1 ppm of methane in the atmosphere at a greater than 0,5 km range in the controlled release tests.
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