Angular momentum state mixing and quenching of n=3 atomic hydrogen fluorescence

281

350

The two-photon resonances of atomic hydrogen (λ = 2 × 205.1 nm), atomic nitrogen (λ = 2 × 206.6 nm) and atomic oxygen (λ = 2 × 225.6 nm) are investigated together with two selected transitions in krypton (λ = 2 × 204.2 nm) and xenon (λ = 2 × 225.5 nm). The natural lifetimes of the excited states, quenching coefficients for the most important collisions partners, and the relevant ratios of the two-photon excitation cross sections are measured. These data can be applied to provide a calibration for two-photon laser-induced fluorescence measurements based on comparisons with spectrally neighbouring noble gas resonances.

Section: Natural Lifetimes and Quenching Coefficientssupporting

confidence: 83%

Absolute calibration of atomic density measurements by laser-induced fluorescence spectroscopy with two-photon excitation

Niemi

Gathen

Döbele

2001

281

350

“…collisional quenching and angular momentum mixing between all three n = 3 states due to collisions after laser excitation. The model developed by Preppernau et al (1995) was employed to account for these corrections. This model predicts the rate of change for the population of each individual state, including both collisional quenching and mixing.…”

Section: Methodsmentioning

confidence: 99%

Femtosecond, two-photon-absorption, laser-induced-fluorescence (fs-TALIF) imaging of atomic hydrogen and oxygen in non-equilibrium plasmas

Schmidt¹,

Roy²,

Kulatilaka³

et al. 2016

Femtosecond, two-photon-absorption laser-induced fluorescence (fs-TALIF) is employed to measure space-and time-resolved distributions of atomic hydrogen and oxygen in moderatepressure, non-equilibrium, nanosecond-duration pulsed-discharge plasmas. Temporally and spatially resolved hydrogen and oxygen TALIF images are obtained over a range of low-temperature plasmas in mixtures of helium and argon at 100 Torr total pressure. The high-peak-intensity, low-average-energy fs pulses combined with the increased spectral bandwidth compared to traditional ns-duration laser pulses provide a large number of photon pairs that are responsible for the two-photon excitation, which results in an enhanced TALIF signal. Krypton and xenon TALIF are used for quantitative calibration of the hydrogen and oxygen concentrations, respectively, with similar excitation schemes being employed. This enables 2D collection of atomic-hydrogen and -oxygen TALIF signals with absolute number densities ranging from 2 × 10 12 cm −3 to 6 × 10 15 cm −3 and 1 × 10 13 cm −3 to 3 × 10 16 cm −3 , respectively. These 2D images are the first application of TALIF imaging in moderatepressure plasma discharges. 1D self-consistent modeling predictions show agreement with experimental results within the estimated experimental error of 25%. The present results can be used to further the development of higher fidelity kinetic models while quantifying plasmasource characteristics.

“…A correction factor was then employed in order to take into account this loss channel in the measured emission line intensities: [15]. In the case of the nitrogen upper state 3p 4 S 0 , the quenching coefficient is not known, so the same values of the H (n = 3) is assumed.…”

Section: Production and Loss Of Excited Statesmentioning

confidence: 99%

Validity of actinometry to measure N and H atom concentration in N₂-H₂direct current glow discharges

Thomaz

Amorim

Souza

1999

Abstract. The validity of actinometry to measure N and H atoms in nitrogen-hydrogen direct current (dc) glow discharges was investigated. The experiments were conducted in positive columns of dc glow discharges, in mixtures of N 2 -xH 2 , where x varies from zero to one, pressures between 133.33 and 533.32 Pa and discharge currents from 1 to 50 mA. The electric fields were measured by electric probes (17 V cm −1 < E < 32 V cm −1 ), and the gas temperatures (490 K < T g < 910 K) were deduced from the rotational transitions of molecular-band systems. The actinometry was performed using argon as the actinometer gas and compared with laser induced fluorescence measurements of ground-state atoms, in order to establish the limits of the validity of actinometry. A theoretical approach was used in order to interpret the behaviour of the emission lines. In nitrogen-hydrogen positive columns, the actinometry method indicated the correct behaviour of the N atoms density in the range of zero to one for x and for H atoms in the region from x = 0 to x = 0.2.