Detection of explosives is an important challenge for contemporary science and technology of security systems. We present an application of NOx sensors equipped with concentrator in searching of explosives. The sensors using CRDS with blue — violet diode lasers (410 nm) as well as with QCL lasers (5.26 μm and 4.53 μm) are described. The detection method is based either on reaction of the sensors to the nitrogen oxides emitted by explosives or to NOx produced during thermal decomposition of explosive vapours. For TNT, PETN, RDX, and HMX the detection limit better than 1 ng has been achieved.
We describe several applications of cavity ring-down spectroscopy (CRDS) for trace matter detection. NO2 sensor was constructed in our team using this technique and blue-violet lasers (395–440 nm). Its sensitivity is better than single ppb. CRDS at 627 nm was used for detection of NO3. Successful monitoring of N2O in air requires high precision mid-infrared spectroscopy. These sensors might be used for atmospheric purity monitoring as well as for explosives detection. Here, the spectroscopy on sharp vibronic molecular resonances is performed. Therefore the single mode lasers which can be tuned to selected molecular lines are used. Similarly, the spectroscopy at 936 nm was used for sensitive water vapour detection. The opportunity of construction of H2O sensor reaching the sensitivity about 10 ppb is also discussed.
Abstract. In the paper, several applications of Cavity Enhanced Absorption Spectroscopy (CEAS) for trace mater detection are described. NO2 sensor was constructed using this technique with blue-violet lasers (395-440 nm). The sensor sensitivity reaches the level of single ppb and it was applied in security portal. For detection of two gases at the same time, two-channel sensor was constructed. Used method allows a significant reduction in the cost of optoelectronic CEAS sensor designed to measure of concentrations of many gases simultaneously. Successful monitoring of N2O and NO in the air requires high precision mid-infrared spectroscopy. The constructed sensors are able to measure concentration at ppb level. These sensors might be used for monitoring of atmospheric purity as well as for detection of explosives.
Application of quantum cascade lasers in NO and N2O sensor is described. Cavity enhanced absorption spectroscopy was used for this purpose. The detection was performed at vibronic molecular transitions in spectral regions of 5.23-5.29 µm and 4.46-4.54 µm for NO and N2O, respectively. In order to avoid interferences by the gases contained in atmosphere (H2O, CO2) the lines of 5.263 µm for NO and 4.530 µm for N2O were selected. Our two channel sensor is designated for simultaneous detection of both compounds. Each channel consists of single mode quantum cascade laser, optical cavity, and a photodetection module. The lasers were precisely tuned to the wavelength of interest. Optical cavities were built with spherical mirrors of high reflectance. The signals from the cavities outputs were registered with specially developed low noise detection modules.
Investigation of nitric oxide and nitrous oxide optoelectronic sensors is described. The detection of both components was done by measurement of absorption that occurs due to transition between vibronic molecular transitions. The improvement of the sensitivity was achieved due to application of cavity enhanced absorption spectroscopy. Two optical cavities (each one for each gas) built of high reectance spherical mirrors were used. While the spectra of observed transitions are situated in mid-infrared range, two single mode quantum cascade lasers were applied. Their narrow emission lines were precisely tuned to the absorption lines of both investigated gases. The measurement of dierent mixtures of ArNO and ArN2O within the range from 100 ppb to 10 ppm was performed. The relative uncertainty of the results did not exceed the level of 13%.
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