Cavity ring down spectroscopy: detection of trace amounts of substance

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.