Spectroscopic detection of biological NO with a quantum cascade laser

Two configurations of a continuous wave quantum cascade distributed feedbac k laser-based gas sensor for the detection of NO at a parts per billion (pp b) concentration level, typical of biomedical applications, have been inves tigated. The laser was operated at liquid nitrogen temperature near lambda = 5.2 mum. In the first configuration, a 100 m optical path length multi-pa ss cell was Employed to enhance the NO absorption. Tn the second configurat ion, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous a nalysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb w hen using CES. The two techniques are compared, and potential future develo pments are discussed.