High-resolution TALIF measurements of atomic oxygen: determination of gas temperature and collisional broadening coefficients

Two-photon Absorption Laser-Induced Fluorescence (TALIF) is a well-established technique to measure relative (and with appropriate calibration techniques, absolute) densities of atoms in plasmas and flames. The excitation line profiles can provide additional information, but this is usually overlooked due to the mediocre spectral resolution of commercial pulsed dye laser systems. We have investigated O-atom TALIF excitation line profiles using a house-built narrow line-width pulsed UV laser system, based on pulsed Ti:Sa ring laser seeded by a cw infrared diode laser. The observed Doppler profiles allow unambiguous measurement of gas temperature with high precision in O$_{\mathrm{2}}$ and CO$_{\mathrm{2}}$ DC glow discharges. Sub-Doppler measurements, performed by reflecting the laser beam back through excitation zone, allow the pressure-broadened line shapes to be observed, both in a pure O$_{\mathrm{2}}$ DC discharge (up to 10 Torr pressure) and in an atmospheric pressure RF plasma jet in He/O$_{\mathrm{2}}$. Pressure broadening coefficients of the 3p$^{\mathrm{3}}P_{J}$ state of O were determined for O$_{\mathrm{2}}$ and He bath gases, and were found to be an order of magnitude bigger than that predicted from the measured quenching rate.