We discuss the use of single-mode cavity ringdown spectroscopy with pulsed lasers for quantitative gas density and line strength measurements. The single-mode approach to cavity ringdown spectroscopy gives single exponential decay signals without mode beating, which allows measurements with uncertainties near the shot-noise limit. The technique is demonstrated with a 10-cm-long ringdown cavity and a pulsed, frequency-stabilized optical parametric oscillator as the light source. A noise-equivalent absorption coefficient of 5 × 10<sup>−10</sup> cm<sup>−1</sup> Hz<sup>−1/2</sup> is demonstrated, and the relative standard deviation in the ringdown time (ς<sub>τ</sub>/τ) extracted from a fit to an individual ringdown curve is found to be the same as that for an ensemble of hundreds of independent measurements. Repeated measurement of a line strength is shown to have a standard deviation <0.3%. The effects of normally distributed noise on quantities measured using cavity ringdown spectroscopy are discussed, formulas for the relative standard deviation in the ringdown time are given in the shot- and technical-noise limits, and the noise-equivalent absorption coefficient in these limits are compared for pulsed and continuous-wave light sources.
© 1999 Optical Society of America
(000.2170) General : Equipment and techniques
(020.3690) Atomic and molecular physics : Line shapes and shifts
(120.3930) Instrumentation, measurement, and metrology : Metrological instrumentation
(300.3700) Spectroscopy : Linewidth
(300.6390) Spectroscopy : Spectroscopy, molecular
Roger D. van Zee, Joseph T. Hodges, and J. Patrick Looney, "Pulsed, Single-Mode Cavity Ringdown Spectroscopy," Appl. Opt. 38, 3951-3960 (1999)