Diode laser spectroscopic measurements of gas temperature in a pulsed dielectric barrier discharge using collisional broadening and shift of 1s3−2p2and 1s5−2p7argon transitions

Abstract

The average gas temperature rise within an argon dielectric barrier discharge operating from 50 to 500 Torr excited by 5 kHz repetition rate fast rise time high voltage pulse has been measured. For these measurements within high pressure discharges, we have employed two novel gas temperature measurement techniques based upon tunable diode laser absorption spectroscopy that take advantage of the nonresonant collision line broadening and collisional frequency shifts from relatively strong argon 1s3-2p2 and 1s5-2p7 transitions from the metastable states. An in situ estimate of collisional broadening coefficients for both transitions have been obtained from 5 to 30 Torr data using an independent estimate of gas temperature from Doppler line width measurements. Our measurements show that the effect of the isolated line assumption inherent within the van der Waals collisional impact approximation limit begins to fail for the 1s3-2p2 and 1s5-2p7 spectral lines when collisional line broadening exceeds ∼23 GHz line separation at gas pressure >300 Torr with gas temperature near ambient. A comparison of gas temperature estimates from both line broadening and peak frequency shift shows that the frequency shift provides a more reliable measurement of gas temperature, indicating that the isolated line assumption holds for collisional peak frequency shifts, even for partially overlapping lines.