Chirped laser dispersion spectroscopy (CLaDS) has been introduced recently as a technique that performs molecular detection based on measurement of optical dispersion. In this paper, a new detection scheme based on chirp modulation (CM) and subsequent phase-sensitive detection is described. CM-CLaDS inherits the full advantages of conventional CLaDS and additionally overcomes some of its limitations. A prototype CM-CLaDS instrument has been developed and characterized in laboratory conditions. The system is based on a distributed feedback quantum cascade laser which operates around 4.52 µm and can probe the most intense nitrous oxide (N2O) ro-vibrational transitions. Preliminary performance tests are presented and provide a path/bandwidth normalized minimum N2O detection limit below 100 ppbv m/Hz1/2.
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