Cavity-enhanced optical frequency comb spectroscopy: application to human breath analysis.

Broad-bandwidth, high-spectral-resolution optical detection of human breath has identified multiple important biomarkers correlated with specific diseases and metabolic processes. This optical-frequency-comb-based breath analysis system comes with excellent performance in all criteria: high detection sensitivity, ability to identify and distinguish a large number of analytes, and simultaneous, real-time information processing. We demonstrate a minimum detectable absorption of 8 x 10(-10)cm(-1), a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 microm where strong and unique molecular fingerprints exist for many biomarkers. We present a series of breath measurements including stable isotope ratios of CO(2), breath concentrations of CO, and the presence of trace concentrations of NH(3) in high concentrations of H(2)O.