Quantitative fs-TALIF in high-pressure NRP discharges: calibration using VUV absorption spectroscopy

Abstract

This work presents a femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic for measuring ground-state atomic nitrogen in nanosecond repetitively pulsed (NRP) discharges. Absolute atom density is obtained from the TALIF signal via a novel calibration technique based on one-photon direct absorption measurements performed in a low-pressure DC discharge. The VUV measurements were done at the Soleil synchrotron facility using the high-resolution Fourier-transform spectrometer (minimum linewidth Δ̃ = 0.08 cm-1). The main goal of this work was to develop a quench-free diagnostic technique, which would allow measurements at elevated pressures with high spatial and temporal resolution. Here fs-TALIF measurements of N(4S) are demonstrated in the NRP post-discharge between 1-500 μs after the nanosecond high-voltage pulse. A maximum number density of N-atoms of × − was measured at 1 μs after the pulse when the discharge was operated at 1 bar in pure nitrogen. This corresponds to a dissociation fraction of ~ 0.1 %. The fs-TALIF technique at high laser intensity regime (> 1 TW cm-2) calibrated using VUV absorption was compared with the fs-TALIF at low laser intensity regime (< 100 MW cm-2) calibrated via the well-established non-saturated TALIF technique using krypton as an etalon gas. It was found that the two measurements of N(4S) in the NRP post-discharge agree within a factor of 3. Importantly, the limit of detection of the fs-TALIF at high laser intensity regime was determined to be ()~ e 1/. This is approximately one order of magnitude better than previously reported by ns-TALIF in low-pressure discharges.

Concentration measurements of atomic nitrogen in an atmospheric-pressure RF plasma jet using a picosecond TALIF

“…The investigations of atomic nitrogen and other reactive species are reported in both low [17][18][19], and high-pressure plasmas [6,20,21]. In low-pressure plasma or environments with inert gases, the reactive atoms in the plasma have a longer lifetime, leading to more efficient surface treatment processes, as the longer-lived reactive species are more likely to interact with and modify the surface of the material being treated, but cost-intensive vacuum techniques are required, which are not affordable in industrial applications [22][23][24][25].…”

Spatially resolved TALIF investigation of atomic oxygen in the effluent of a CO2 microwave discharge

“…with durations in the fs range [28]. However, the lower peak powers of ns pulses help avoid unwanted effects such as saturation that might otherwise complicate the calibration procedure necessary to obtain absolute number densities [29,30].…”

Absolute N-atom density measurement in an Ar/N2 micro-hollow cathode discharge jet by means of ns-two-photon absorption laser-induced fluorescence

“…The ground state of atomic nitrogen (2p 3 ) 4 S 0 3/2 is only accessible in the vacuum ultraviolet (VUV) range, which can be probed using absorption spectroscopy, but it requires a UV radiation source and vacuum environment. To circumvent the need for VUV facilities, Two-photon Absorption Laser Induced Fluorescence (TALIF) was introduced and successfully used to probe the density of N atoms in various plasma sources 25,26 . TALIF is a highly sensitive technique with a very good spatial and temporal resolution.…”