Cavity ring-down spectroscopy for atmospheric pressure plasma jet analysis

Abstract

Pulsed cavity ring-down spectroscopy (CRDS) is a direct absorption, highly sensitive, versatile technique suitable for the analysis of a wide range of plasmas. CRDS belongs to a wide class of cavity-enhanced spectroscopies. This work briefly describes the basic principles of CRDS and summarizes the main literature specifically related to applications for atmospheric pressure plasma jets (APPJ). Emphasis is given to the temporal resolution and pulsed character of the plasma sources. As an example we present in more detail the determination of metastable helium density in the 2s S 3 1 state produced in a single-electrode atmospheric pressure plasma jet driven by a pulsed high-voltage waveform. Measured He( S 3 1 ) number densities ranged from × −

Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

“…Cavity enhanced absorption spectroscopy incorporates several techniques [233] including cavity ring-down (CRD) spectroscopy. As described in a recent paper [234], when a light pulse enters the cavity, the signal at the exit of the cavity is therefore a decaying signal of the subsequent sequence of pulses each with a lower intensity than the previous one. The pulse peak values follow an exponential decay, which is dependent on the reflectivity of the cavity.…”

“…I 0 is the incident light intensity, L is the cavity length, R the reflectivity of the mirrors and c is a constant depending on the time a light beam takes to travel back and forth in a cavity of length L. Here, τ 0 characterizes the lifetime of a laser pulse in a cavity and depends on the transmission coefficient of the mirrors of the cavity without any absorbing medium. If an absorbing medium of length l is introduced into the cavity, the effective pulse lifetime is reduced and the absorber density N can be calculated by [234]: ,…”

“…Due to its excellent sensitivity, cavity-enhanced methods, especially cavity ring down spectroscopy have found broad application in diagnostics of low-pressure plasmas [236][237][238]. This technique is increasingly being used for the studies of N-APPJs [234,239]. High time resolution and possible space resolution are advantages of the high-sensitivity method [146,239].…”

Detection of HO2in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy

“…Similarly, CRDS has been employed for the detection of species in plasmas. An overview of the existing applications of CRDS to characterize various types of atmospheric pressure plasma jets can be found in [23]. In this paper, we utilize the related technique of OF-CEAS in which the laser is scanned over the spectral region of interest and locks, through optical feedback, to successive cavity resonances.…”

Study of time constant variation with concentration of a Gas in a Pulsed - Cavity Ring Down Spectroscopy.

“…Laser Source selection:-While designing an optical resonator the relationship between the spectral widths of the incident light Δ ω laser (laser pulse) the absorption line to be studied ω abs and the distance of the neighboring longitudinal modes need to satisfy the following condition [3]. ω abs > Δω laser > Δω modes…”