Abstract

The absorption spectra and wavelength modulation spectroscopy (WMS) of NO2 using a tunable, external cavity CW quantum cascade laser operating at room temperature in the region of 1625 to 1645cm1 are reported. The external cavity quantum cascade laser enabled us to record continuous absorption spectra of low concentrations of NO2 over a broad range (16cm1), demonstrating the potential for simultaneously recording the complex spectra of multiple species. This capability allows the identification of a particular species of interest with high sensitivity and selectivity. The measured spectra are in excellent agreement with the spectra from the high-resolution transmission molecular absorption database [J. Quant. Spectrosc. Radiat. Transfer 96, 139–204 (2005)]. We also conduct WMS for the first time using an external cavity quantum cascade laser, a technique that enhances the sensitivity of detection. By employing WMS, we could detect low-intensity absorption lines, which are not visible in the simple absorption spectra, and demonstrate a minimum detection limit at the 100ppb level with a short-path absorption cell. Details of the tunable, external cavity quantum cascade laser system and its performance are discussed.

© 2009 Optical Society of America

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