A study has been performed to re-investigate the actinometric technique used to determine the absolute concentration of O atoms in DC O2 flowing glow discharges for pressures ranging from 0.36 to 2 Torr and discharge currents ranging from 5 to 80 mA in Pyrex tubes of three different diameters (16, 7 and 4 mm). Actinometric measurements using O(3P-3S) 844 nm, O(5P-5S) 777 nm and Ar(2p1-1S2) 750 nm transitions are compared to VUV absorption spectrometry. The choice of the excitation cross sections for the calculations of atomic excitation rates as a function of the reduced electric field using a Boltzmann code and the contribution of the quenching processes of the excited states are discussed. The dissociation ratio (O)/(O2) can be determined from the ratio of intensities I844/I750 by the relation (O)/(O2)=C3P2p1 I844/I750. We have found that C3P2p1 remains constant (C3P2p1=2.6*10-3) throughout the range of experimental conditions investigated. The recombination probability gamma of the O atoms at the wall is calculated and correlated to the wall temperature of the Pyrex tubes. The variation of the recombination probability as a function of the wall temperature is fitted by the relation gamma =0.94exp(-1780/Twall) for 300

Laser-induced fluorescence (LIF) techniques currently used as an optical diagnostic to study and characterize non-thermal equilibrium plasmas are reviewed. The general mechanisms occurring in one- or two-photon resonant absorption-induced fluorescence when used for the detection of species in their fundamental state are analysed. We emphasize the techniques based on the simultaneous absorption of two photons for the detection of light atoms and molecules and, particularly, two-photon absorption laser-induced fluorescence (TALIF) and derivative techniques, such as resonant enhanced multi-photo-ionization, two-photon absorption laser-induced stimulated emission (TALISE) and photo-fragment translational spectroscopy, in which molecules are photo-dissociated and the ejected atomic fragments are simultaneously detected by TALIF. The kinetics of one- and two-photon absorption are treated in detail including, for the latter, a modelling, which indicates the conditions of emergence of TALISE. The main calibration methods allowing one to obtain the absolute density of species detected by LIF and some examples of applications demonstrating the interest of these diagnostic techniques in plasma processing are presented.

Laser optogalvanic and fluorescence spectroscopy in glow discharge plasmas AIP Conf.

Densities of N, H, and NH active species have been detected by laser-induced fluorescence (LIF) in N2-KEY WORDS: Laser-induced fluorescence; flowing dc discharge; N2-H2 mixture.

Absolute nitrogen atom density measurements by two-photon laser-induced fluorescence spectroscopy in atmospheric pressure dielectric barrier discharges of pure nitrogen Absolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging J. Appl. Phys. 85, 696 (1999); 10.1063/1.369149Twophoton laserinduced fluorescence measurements of absolute atomic hydrogen densities and powder formation in a silane discharge

Direct current N 2 flowing discharges were generated and conditions for the pink afterglow were obtained. Emissions from N 2 (B, C) and N + 2 (B) radiative states were studied as a function of pressure, flow rate and post-discharge position. A one-dimensional kinetic model accounting for N 2 (X, v), N 2 (A, B, C, a, a , a ), N( 4 S), N + 1−4 (X) and N + 2 (B) species has been developed in order to describe the experimental observations. The analysis on the complete set of processes assumed in this paper has provided possible generation mechanisms for N atoms, N + 2 (B) ions and N 2 (B, C) electronically excited states as well as for metastable ones. It has been shown that ionization, excitation and dissociation processes occur simultaneously at the post-discharge region when the vibrational distribution function of N 2 (X, v) states heats as resulting from the efficient V-V pumping mechanism, which is very sensitive to pressure conditions. Here, the pink afterglow is described as a non-equilibrium plasma, i.e. ambipolar diffusion for ions and the condition of charge neutrality are assumed.

Experimental observations concerning the formation of a high-density plasma in an inductively coupled radio frequency (11.4 MHz) discharge in argon are described. These observations are complemented by probe measurements that provide a quantitative description of plasma properties over an useful range of vapor pressure, 0.02–0.2 Torr, and rf power, 50–400 W. It is shown that a dense plasma of the order of 1012 cm−3 can be easily formed, having the configuration of a luminous plasmoid embedded in a low-density, 1010 cm−3, diffuse plasma.

Optical emission spectroscopy and laser-induced fluorescence (LIF) techniques are used to study the production of active species in DC and HF N 2 -H 2 and N 2 -H 2 -Ar flowing discharges and post-discharges, in connection with plasma reactions for surface treatments. N and H ground state atom relative densities are obtained by two-photon LIF in a N 2 -H 2 flowing DC discharge and in the DC and HF post-discharge regions. The conditions to create maximum density of N and H species are determined in each case in relation to the plasma kinetics. In no case was the NH radical observed in the post-discharge regions, indicating that this radical does not contribute to the nitriding process.