Gar W. Truong, Kevin O. Douglass, Stephen E. Maxwell, Roger D. van Zee, David F. Plusquellic, Joseph T. Hodges, David A. Long
Challenging applications in trace gas analyses require high precision and acquisition rates.1-4 Many continuous-wave laser spectroscopy techniques exhibit significant sensitivity and potential;5 however, their scanning rates are slow because they rely upon either mechanical or thermal frequency tuning.6 Herein we present frequency-agile rapid scanning spectroscopy in which a high bandwidth electro-optic modulator is utilized to step a selected laser sideband of a stabilized laser to successive modes of an optical cavity. This approach involves no mechanical motion and enables the acquisition of absorption spectra at rates of up to 200 Hz, a rate that is limited only by the cavity response time itself. This technique is over four orders of magnitude faster than traditional continuous-wave cavity ring-down spectroscopy.6 Spectrum ranges exceeding 100 GHz should be possible through the use of high-speed microwave sources. Measurements of carbon dioxide are presented which exhibit a sensitivity of 2×10-11 cm-1 Hz-1/2 and a frequency accuracy of 10 kHz. This technique shows exceptional promise for fast and sensitive trace gas measurements as well as studies of chemical kinetics and reaction dynamics.