Trace-gas sensing is a rapidly developing field, in demand for applications such as breath diagnostics, process and air-quality monitoring, atmospheric measurements, and security and surveillance. Quantum cascade lasers have dramatically affected the field of trace-gas sensing, increasing the sensitivities of detectors that are becoming smaller and more convenient almost monthly. And the development of CW versions of the lasers promises to enable more advances.

Breath analysis is a noninvasive medical diagnostic method that addresses more than 200 compounds in exhaled breath.¹ Many of these compounds can be used to identify particular medical conditions — if they can be measured accurately at very low concentration levels, typically in the range of a few parts per billion. Moreover, this must be accomplished using a small sample volume and a simple-to-use device...