Amplitude modulated multimode-diode-laser-based cavity enhanced absorption spectroscopy with a phase-sensitive detection for high-sensitivity NO2 detection

<p>Accurate and sensitive measurements of NO₂ play an extremely important role in atmospheric studies. In the past 20 years, high sensitivity, precision, and accurate NO₂ detection technology has developed rapidly, especially optical methods based on high-finesse cavities. In combination with chemical conversion, NO₂ detector is used to measure a range of other important reactive atmospheric species, such as total reactive nitrogen (total peroxy nitrate (&#931;PNs), total alkyl nitrate (&#931;ANs), and nitric acid (HNO₃)), total peroxy radicals, O₃ and nitric oxide (NO), which greatly enhanced our understanding of nitrogen chemistry, free radical chemistry, and atmospheric oxidation capacity.</p><p>In this presentation, we will report the development of an Amplitude Modulated multimode-diode-laser-based Cavity Enhanced Absorption Spectroscopy (AM-CEAS) system operating at 406 nm that uses phase-sensitive detection for extremely sensitive NO₂ detection. A detection limit of 35 pptv (1&#963;, 1s) was achieved with reflectivity <em>R</em> ~ 99.985% (ring-down time &#964;₀ ~ 10.87 &#956;s). When the integration time was extended to 30 s, the precision can be further improved to 8 pptv. The reported AM-CEAS method provides a powerful, straightforward, and general method for ultra-sensitive absorption and extinction measurements.</p>