The Development of Cavity Ringdown Spectroscopy as a Sensitive Continuous Emission Monitor for Metals
The aim of this study is to evaluate cavity ringdown spectroscopy (CRDS) as an ultra-sensitive technique for trace analysis of metals. Potential applications of CRDS meeting the Department of Energy needs include: Mercury Continuous Emission Monitor Multi-Metal Emissions Monitor Radionuclide Detector and Monitor CRDS is based upon the measurement of the rate of light absorption in a closed optical cavity. A laser pulse is injected into a stable optical cavity through one of the cavity mirrors. This light pulse is trapped between the mirror surfaces and decays exponentially over time at a rate determined by the round trip losses within the cavity. When used for trace analysis, the primary loss mechanisms governing the decay time are mirror reflectivity losses, atomic absorption from the sample, and Rayleigh scattering from air in the cavity. The decay time is given by t= d c 1- R ( )+ als + bd [ ] (1) where d is the cavity length, R is the reflectivity of the cavity mirrors, a is the familiar Beer's Law absorption coefficient of a sample in the cavity, ls is the length of the optical path through the sample (i.e., approximately the graphite furnace length), b is the wavelength-dependent Rayleigh scattering attenuation coefficient, and c is the speed of light. Thus, variations in a caused by changes in the sample concentration are reflected in the ringdown time. As the sample concentration increases (i.e., a increases), the ringdown time decreases yielding an absolute measurement for a. With the use of suitable mirrors, it is possible to achieve thousands of passes through the sample resulting in a significant increase in sensitivity. An additional benefit is that it is not subject to collisional quenching, the branching of fluorescence emission into multiple transitions, and the ability to detect only a fraction of the fluorescence photons that occur in laser-excited atomic fluorescence (LEAFS). One other advantage of the ringdown technique is the ability to use pulsed UV tunable lasers for atomic absorption spectroscopy.
- Research Organization:
- Mississippi State University, Starkville, Mississippi (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- DOE Contract Number:
- FG07-97ER62517
- OSTI ID:
- 828512
- Report Number(s):
- EMSP-60070-1999; R&D Project: EMSP 60070; TRN: US200427%%445
- Resource Relation:
- Other Information: PBD: 1 Jun 1999
- Country of Publication:
- United States
- Language:
- English
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