Gas temperature measurements in a high pressure argon pulsed dielectric barrier discharge using diode laser absorption spectroscopy

Summary form only given. A tunable diode laser absorption spectroscopic technique has been used to quantify the high-pressure (p= 100-500 Torr) scaling of gas temperature in an argon dielectric barrier discharge (DBD) excited using two different applied unipolar voltage pulses from 1.7-6.0 kV and <;800μJ/pulse maximum deposited energy. The diode laser tuning range was sufficient to capture both collision-broadened "wings" of the 1s₃-2p₂ (772.42 nm) and 1s₅-2p₇ transitions simultaneously in a single scan. The diagnostic technique is based upon Lindholm-Foley theory¹ which is particularly applicable for highly nonequilibrium discharge conditions in which the Lorentzian line shape dominates over the Doppler component. Along with the ideal gas law, Lindholm-Foley theory can be used to express both "shift" and "collision width" temperatures as T_s=T_o(β_op/β)^10/7 and T_c=T_o(2Γ_op/2Γ)^10/7, respectively, where T_s =300 K, β_o, and 2Γ_o are the reduced shift and broadening coefficients for a specified transition. In order to use this method to measure small gas temperature changes, it is important to obtain accurate values of β_o and 2Γ_o for each transition. Measurements of 2Γ_o were not found in literature², while β_o was found to be systematically biased². Estimates of these coefficients were performed using a self-consistent in situ cross-calibration incorporating both transitions, (i) low pressure measurements of 2Γ_o and (ii) high pressure measurements of the absolute shifts and line widths. Low pressure (p=5-50 Torr) measurements gave 2Γ_o(1s₃-2p₂)=22.8±1.0 MHz/Torr and 2Γ_- (1s₅-2p₇)=21.6±0.3 MHz/Torr. Frequency shift measurements were performed by comparing absorption peaks obtained simultaneously from the DBD and a 1 Torr argon dc discharge. The 2Γ measurements were obtained from Voigt profile fitting. Lindholm-Foley theory predicts that β/2Γ=β_o/2Γ_o ≈ -0.3627. Our measurements indicate that β_o2Γ_o=-0.333±0.025 for both transitions so that within the specified uncertainties, β_o(1s₃-2p₂)≈-7.6±0.7 MHz/Torr and β_o(1s₅-2p₇)≈-7.2±0.5 MHz/Torr. Over the range of pressure and voltages, the measured gas temperature was nearly constant at 330±30 K.