Abstract

In this paper, results are presented that demonstrate an infrared cavity ringdown spectrometer capable of rapid, uninterrupted tuning over a spectral range of over 200 cm⁻¹. This work addresses the need for a fieldable infrared sensor that can fully exploit the high sensitivity and specificity offered by laser-based IR spectroscopy when conducted in the fundamental absorption regions. To achieve maximum specificity, such a device would tune over significant fractions the fundamental absorption regions near 8-14 µm and 3-5 µm. This would allow measurement of multiple vibrational band systems of larger molecules in addition to resolving individual rovibrational lines of smaller species. The system described here is shown to tune continuously over 200 cm⁻¹ segments in the latter spectral window. By combining more than one continuous scan, it is possible to cover the full CH-stretching range (3.1-3.7 µm). Ultimately, tuning is limited only by the spectral bandwidth (600 cm⁻¹) of the ringdown mirrors that are used. Future systems can extend this technique to the 8-14 µm window.

© 2000 Optical Society of America