Cavity ring-down spectroscopy with a pulsed distributed feedback quantum cascade laser

Abstract

A pulsed distributed feedback quantum cascade laser operating near 970 cm-1 (10.3 μm) was coupled with the technique of cavity ring-down spectroscopy, as described here for the first time. The newly constructed set-up was tested by recording three relatively weak rotational lines of the 1000→0001 vibrational band of CO2 in the range from 966.75 cm-1 to 971.5 cm-1. The CO2 lines were recorded by measuring the decay time of a CO2 - N2 mixture flowing through an open sample tube placed between the cavity ring-down mirrors. The quantum cascade laser frequency was tuned at a rate of ~ 0.071 cm-1/K by changing the heat sink temperature in the range between -20 and 50 °C. The first results demonstrated the applicability and high sensitivity of the cavity ring-down spectroscopy - pulsed quantum cascade laser combination and encouraged us to extend our research to the study and detection of ammonia. We demonstrated that a detection limit of ammonia of ~ 25 ppbv can be attained with the current set-up. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement are discussed.