Parts-per-trillion-level detection of nitrogen dioxide by cantilever-enhanced photo-acoustic spectroscopy

We present a simple and highly sensitive cantileverenhanced photo-acoustic sensor for detection of nitrogen dioxide. A noise equivalent detection limit of 50 parts-per-trillion in 1 s is demonstrated. The limit was reached with an average optical power of 4.7 W using a continuous-wave laser at 532 nm. The achieved normalized noise equivalent absorption coefficient was 2.6 ¡Á 10.10 Wcm.1 Hz.1 M2