Plasma-cavity ringdown spectroscopy (P-CRDS) for elemental and isotopic measurements

et al. 2015

Appl. Phys. B

radical-based chemistry generally dominates in any eventual material processing in the plasma jet.The CH radical is a common intermediate in reactive chemical systems with hydrocarbons [6]. Monitoring CH provides an insight into the reaction mechanism. CH radicals and C atoms contribute to the experimentally observed high and nonuniform diamond growth rates in the highpower Bristol reactor [7]. The level of CH concentration agreement between the model prediction and the experimental measurement can be used to test model predictions of hydrocarbon chemistry [8]. CH also is a probe species to determine the chemical erosion of carbon-based materials in divertor [9].Optical emission spectroscopy (OES) is arguably the simplest and most straightforward means to investigate the CH behavior in the plasma. The OES signal is proportional to the population density of the upper state, and the interpretation of OES data is complicated which needs a proper understanding of the various species excitation and de-excitation processes, especially when the plasma does not close to local thermodynamic equilibrium (LTE). Generally, the ground electronic state radicals and molecules are inevitably present in higher concentrations than their electronically excited counterparts and dominate the thin film deposition [10]. Thus, it is necessary to measure the majority species populating ground and low-lying electronic states.To diagnose the ground state, absorption spectroscopy is a preferred approach. Cavity ring-down spectroscopy (CRDS) [11] provides the diagnostic of choice to obtain the absolute number densities without the need for additional calibration standards. The technique measures the time decay of a laser pulse trapped in a high-finesse optical cavity. Effectively, it is a multi-pass technique in which the optical path length may be tens of kilometers. Thus, it is a versatile, highly sensitive, linear absorption technique.Abstract A combination of optical emission spectroscopy (OES) and cavity ring-down spectroscopy (CRDS) has enabled to determinate the number densities of CH(A 2 Δ) and CH(X 2 Π) radicals simultaneously in a cascaded arc plasma reactor operating with a CH 4 /Ar mixture. It is found that the number density of CH(A 2 Δ) radical increases with discharge current at first and then decreases. However, the number density of CH(X 2 Π) radical decreases with discharge current when the rate of CH 4 flow to total flow is lower than 1 %, while it increases slightly with discharge current when the rate is 1.5 %. The results reveal that CH radicals are deviation from excitation equilibrium. Although OES is the simplest and most straightforward means to investigate the CH radical behavior, it is not enough to provide the information of the CH(X 2 Π) number density, and additional methods, such as CRDS, are needed in the cascaded arc plasma jet.

Section: Crds Systemmentioning

confidence: 99%

Determination of the number densities of CH(X2Π) and CH(A2Δ) radicals in a DC cascaded arc discharge plasma

et al. 2015

Appl. Phys. B

“…The MPT used in the present work was similar to the one discussed in previous reports. 41,43 Plasma was supported by argon gas (99.99%, Airgas). The sample injection was made through the inner tube of the MPT, which was connected to the nebulizer by a thin tubing (Nalgene).…”

Section: B Oes Modementioning

confidence: 99%

“…Two small (7 mm × 4 mm) side windows, diametrically opposite to each other, were created in the wall of the MPT chamber that housed the MPT, so that the laser beam could pass through the plasma plume. The measuring principle of the plasma-CRDS technique is based on 36,41 …”

Section: Crds Modementioning

confidence: 99%

A portable optical emission spectroscopy-cavity ringdown spectroscopy dual-mode plasma spectrometer for measurements of environmentally important trace heavy metals: Initial test with elemental Hg

Sahay

Scherrer

Review of Scientific Instruments

2012

Self Cite

A portable optical emission spectroscopy-cavity ringdown spectroscopy (OES-CRDS) dual-mode plasma spectrometer is described. A compact, low-power, atmospheric argon microwave plasma torch (MPT) is utilized as the emission source when the spectrometer is operating in the OES mode. The same MPT serves as the atomization source for ringdown measurements in the CRDS mode. Initial demonstration of the instrument is carried out by observing OES of multiple elements including mercury (Hg) in the OES mode and by measuring absolute concentrations of Hg in the metastable state 6s6p (3)P(0) in the CRDS mode, in which a palm-size diode laser operating at a single wavelength 405 nm is incorporated in the spectrometer as the light source. In the OES mode, the detection limit for Hg is determined to be 44 parts per 10(9) (ppb). A strong radiation trapping effect on emission measurements of Hg at 254 nm is observed when the Hg solution concentration is higher than 50 parts per 10(6) (ppm). The radiation trapping effect suggests that two different transition lines of Hg at 253.65 nm and 365.01 nm be selected for emission measurements in lower (<50 ppm) and higher concentration ranges (>50 ppm), respectively. In the CRDS mode, the detection limit of Hg in the metastable state 6s6p (3)P(0) is achieved to be 2.24 parts per 10(12) (ppt) when the plasma is operating at 150 W with sample gas flow rate of 480 mL min(-1); the detection limit corresponds to 50 ppm in Hg sample solution. Advantage of this novel spectrometer has two-fold, it has a large measurement dynamic range, from a few ppt to hundreds ppm and the CRDS mode can serve as calibration for the OES mode as well as high sensitivity measurements. Measurements of seven other elements, As, Cd, Mn, Ni, P, Pb, and Sr, using the OES mode are also carried out with detection limits of 1100, 33, 30, 144, 576, 94, and 2 ppb, respectively. Matrix effect in the presence of other elements on Hg measurements has been found to increase the detection limit to 131 ppb. These elements in lower concentrations can also be measured in the CRDS mode when a compact laser source is available to be integrated into the spectrometer in the future. This exploratory study demonstrates a new instrument platform using an OES-CRDS dual-mode technique for potential field applications.

“…(76) Very recently, Wang has reviewed plasma cavity ringdown spectroscopy (P-CRDS) for elemental and isotopic measurements ( Figure 1). (77) The purpose of this article is to provide an update of the previous review (71) on the application of CRDS in analytical and atomic spectroscopy by Miller and Winstead in 2000. The discussion attempts to cover a wide range of applications of CRDS with a new emphasis in this article on environmental monitoring, the latest developments in P-CRDS for elemental and isotopic measurement, and combustion flame chemistry and plasma diagnostics.…”

Section: Introductionmentioning

confidence: 99%

“…A review of P-CRDS for elemental and isotopic measurements has recently been published. (21,77) This section incorporates an update on the development of the P-CRDS technique since the last review. Emphasis is placed on the improvement of the P-CRDS technique and isotopic measurements.…”

Section: Introductionmentioning

confidence: 99%

Cavity Ringdown Laser Absorption Spectroscopy

Encyclopedia of Analytical Chemistry

Miller

Winstead

2008

Self Cite

Cavity ringdown spectroscopy (CRDS) has developed rapidly during the last two decades and has been implemented for a variety of applications ranging from fundamental spectroscopic studies, trace chemical detection for environmental monitoring, combustion flame chemistry and plasma diagnostics, elemental and isotopic measurements, breath gas analysis, and fiber ringdown chemical and physical sensor development. A host of chemical species, including atoms, ions, molecules, clusters, and free radicals, have been studied by CRDS. The experimental ringdown scheme has also evolved from an original mirror‐based format to various new forms for detection and analysis of analytes in either gas phase or liquid solutions. Recent research effort has also extended the CRDS approach for fiber optical sensor development. CRDS has become a mature spectrometric technique for a range of prototype and commercial instrumentation. This article provides a review of the latest developments in CRDS applications, specifically emphasizing new trends in elemental and isotopic analysis, plasma diagnostics, breath gas analysis, and new fiber ringdown techniques for sensor development. The introduction of cutting‐edge laser sources into CRDS methods, the combination of CRDS with conventional analytical tools, and current CRDS instrumentation are also briefly discussed.