Quantum cascade laser-based carbon monoxide detection on a second time scale from human breath

We present three different detection schemes for measuring carbon monoxide (CO) in direct absorption using a thermoelectrically cooled, distributed-feedback pulsed quantum cascade (qc) laser operating between 2176 and 2183 cm-1. The laser emission has overlap with the strong R(8)1 ro-vibrational transition in CO at 2176.2835 cm-1. Firstly, by utilizing the frequency chirp of the qc-laser with long laser pulses, a minimal detectable absorption of 1.2X10-5 cm-1 is achieved at an acquisition rate of 3 Hz. Additionally, with short laser pulses and slow frequency scanning a minimal detectable absorption 8.2X10-7 cm-1 is reported, with an acquisition time of 60 s. Finally, a novel amplitude modulation technique is developed to facilitate real-time measurement of CO in exhaled air. The application of this detector to detection of CO in a single breath as a potential non-invasive diagnostic tool is shown.