The influence of vibrational excitation on the burning voltage of a pulsed electric discharge in HF laser working media

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The burning voltages of an intermediate pressure self-sustained volume discharge (SSVD) in SF6 and SF6-C2H6 mixtures irradiated by a 10.6 μm pulse TEA CO2 laser, have been measured on varying the laser fluences over a wide range. The delay between the voltage application and the laser pulse onset is 4 μs, and the laser pulse lasts ∼3 μs. The considerable rise observed in the discharge voltages with increasing absorbed specific laser radiation energy, is due to electron attachment to vibrationally excited molecules of SF6. Different processes of relaxation of the vibrational energy stored in SF6 molecules are analyzed and the relevant characteristic times are numerically assessed. The gas heating process owing to vibration-translation energy exchange is qualitatively described in terms of the “thermal explosion”. The relation between the “explosion” and delay times determines the peculiarities of electron attachment to vibrationally excited SF6 molecules. The burning voltages of a submicrosecond non-irradiated SSVD in the above-mentioned media versus the specific electric energy deposited are also measured. They are compared to those of a laser-illuminated SSVD at commensurable specific laser energy depositions. It is concluded that electron attachment to the discharge-produced vibrationally excited SF6 molecules is not capable of noticeably affecting the discharge voltages of a submicrosecond non-irradiated SSVD.