Cavity Ringdown Spectroscopy for Diagnostic and Analytical Measurements in an Inductively Coupled Plasma

Abstract

The use of cavity ringdown spectroscopy (CRDS) for atomic absorption measurements in a 27-MHz low-power argon inductively coupled plasma (ICP) is described. These results are used to demonstrate the utility of CRDS for both plasma diagnostic and analytical measurements. In these experiments, an aqueous solution of lead was introduced into a modified torch designed to enhance the ICP conditions for atomic absorption measurements. Absorption intensity characteristics of the lead 283.3-nm absorption line as a function of observation height and lateral position in the plasma were recorded for three different ICP powers (700, 500, and 200 W). The radial distribution of the ground-state lead atom density was derived from Abel inversion of the lateral measurements. At the novel 200 W operating condition, spectral line shapes vs. height and lateral position were fitted to Voigt profiles. Line-of-sight values of the gas kinetic temperature and electron density at different plasma locations were estimated from Gaussian and Lorentzian broadening components, respectively. The results are discussed and compared with those from other methods. The unique flexibility of CRDS for atomic and ionic absorption measurements in an ICP and the potential application of the ICP-CRDS technique for analytical measurements are demonstrated. Analytical results are compared with theoretical estimates of the lead detection limit.

Cavity Ring-down Spectroscopy for Detection in Liquid Chromatography: Extension to Tunable Sources and Ultraviolet Wavelengths

“…Whereas UV-CRDS measurements in the gas phase start to become successful, 16,18 liquid-phase UV-CRDS is hampered by the rather stringent constraints on required mirror reflectivities, which can currently not yet be met at wavelengths in the deep UV.…”

Cavity Ringdown Laser Absorption Spectroscopy

“…(53) They also measured the temporally resolved N 2 + concentration in a pulsed atmospheric pressure N plasma. (104) Wang et al (20) measured concentration and lineshapes of atomic lead transitions at 283 nm in different vertical and lateral positions of an atmospheric argon ICP. Fitting a lineshape into a Voigt lineshape yields Doppler and Lorentzian components, from which plasma gas kinetic temperature and electron density were estimated.…”

“…10-15%, for plasma diagnostics. (20,151,156) Another relatively new CRDS-related application is sputtering plasma monitoring. Ion beam sputtering plasma is created when an energetic ion beam bombards the surface of a metallic target.…”

“…Including losses resulting from the hightemperature atmospheric plasma and the open-air cavity, the observed ringdown time in a P-CRDS system can be expressed as (20) in Equation (11):…”

“…Using the experimental lineshape data to determine the average cross section allows for the measurement of the average density of atoms or ions in the lower state of the transition to be probed. For the purpose of plasma diagnostics, such as measuring the distribution profile of electron density, gas kinetic temperature, and analyte/species density, the line-of-sight measurement may generate a large deviation (20,151,156,187,188) ; Abel inversion may be used to convert the lateral measurements to the radial distributions. (20,189) However, for analytical applications in which the detection sensitivity is the quantity of concern, the line-of-sight measurement is appropriate.…”