Quantitative analysis of decay transients applied to a multimode pulsed cavity ringdown experiment

Abstract

The intensity and noise properties of decay transients obtained in a generic pulsed cavity ringdown experiment are analyzed experimentally and theoretically. A weighted nonlinear least-squares analysis of digitized decay transients is shown that avoids baseline offset effects that induce systematic deviations in the estimation of decay rates. As follows from simulations not only is it a method that provides correct estimates for the values of the fit parameters, but moreover it also yields a correct estimate of the precision of the fit parameters. It is shown experimentally that a properly aligned stable optical resonator can effectively yield monoexponential decays under multimode excitation. An on-line method has been developed, based on a statistical analysis of the noise properties of the decay transients, to align a stable resonator toward this monoexponential decay.

Evanescent-Wave Cavity Ring-Down Spectroscopy for Enhanced Detection of Surface Binding under Flow Injection Analysis Conditions

“…As previously discussed, excitation with narrow-band radiation from injection-seeded Nd:YAG lasers would result in mode-beating on the transients, 23 and therefore the 532 nm radiation at sufficiently large bandwidth was produced through the use of an optical parametric oscillator (OPO) pumped with the third harmonic of a Coherent Infinity single-mode Nd:YAG laser (Santa Clara, CA) at 355 nm; 2 this laser has the advantage that the repetition frequency can be varied between 10 and 100 Hz without modifications to the beam profile.…”

Cavity Ring-Down Spectroscopy of O2–O2 Collisional Induced Absorption

“…As was elaborated by Naus et al [4] a weighted non-linear least-squares fit to the data on the transient give the best determination of the decay life time, and in particular produces a reliable estimate of the uncertainty. As for the optical resonator it is important that it is aligned such that its mode structure does not result in wavelength-dependent effects.…”

“…The optical resonator then acts as a white-light filter and the configuration can be used for wavelength-scanning pulsed CRDS. The relation between mode-structure and transmission, and an experimental method to improve alignment towards single-exponential decay in a non-confocal resonator were discussed in reference [4].…”

Liquid-Phase and Evanescent-Wave Cavity Ring-Down Spectroscopy in Analytical Chemistry

“…If the transverse modes are suppressed, the equation takes the form of the equally spaced ( ν = c 2L spaced) transmission fringes of an etalon; this condition can be most easily met under confocal conditions (L = R c ). If transversal modes are excited, and if the resonator length is sufficiently far away from the confocal condition, the filling-in of transverse modes may become so dense that the resonator becomes a white-light attenuator/transmitter (53). This condition is particularly useful for cavity ring-down experiments, as the transmission of the resonator (and therefore the ring-down properties) becomes wavelength independent.…”