van Zee R D, Hodges J T, Looney J P
Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8364, USA.
Appl Opt. 1999 Jun 20;38(18):3951-60. doi: 10.1364/ao.38.003951.
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 x 10(-10) cm(-1) Hz(-1/2) is demonstrated, and the relative standard deviation in the ringdown time (sigma(tau)/tau) 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.
我们讨论了使用带有脉冲激光器的单模腔衰荡光谱技术进行气体密度定量测量和谱线强度测量。单模腔衰荡光谱技术可产生无模式拍频的单指数衰减信号，这使得测量的不确定度接近散粒噪声极限。我们使用一个10厘米长的衰荡腔和一个脉冲、频率稳定的光学参量振荡器作为光源来演示该技术。实验展示了5×10⁻¹⁰厘米⁻¹赫兹⁻¹/²的等效噪声吸收系数，并且从单个衰荡曲线拟合中提取的衰荡时间的相对标准偏差（σ(τ)/τ）与数百次独立测量的总体结果相同。对谱线强度的重复测量显示其标准偏差小于0.3%。讨论了正态分布噪声对使用腔衰荡光谱技术测量的量的影响，给出了散粒噪声和技术噪声极限下衰荡时间相对标准偏差的公式，并比较了脉冲光源和连续波光源在这些极限下的等效噪声吸收系数。
