Deionization of afterglow plasma of pulsed lasers through intensified ambipolar diffusion

Abstract

Method of electron concentration (lIe) reducing in an interpulse period is proposed, based on ambipolar diffusion (AD) rate increase to the tube walls. As the AD coefficient D = D(1Te/T), the heating of electrons by weak electric field to the Te 1 3B , yet insufficient for ionization although much higher than the gas temperature T, considerably hastens the process of ion removal to the walls. Effect of the intensified ambipolar diffusion (TAD) was registered experimentally by us in the afterglow of zinc and cadmium metal vapor ion lasers. In this work, computer modeling of the lAD is performed for He-Cu and Ne-Cu discharge afterglows with parameters typical for self-terminated copper vapor laser. As the calculations demonstrate, at helium pressure of about 10 Torr and tube diameter 1 cm, when heating field E of 0.8-0.9 V/cm is imposed on afterglow for a time period of 100 ts, e slides down to values of 1O2lO4 times smaller as compared to those without heating. The effect is stronger in helium. The use of lAD in interpulse period would allow, as calculations reveal, up to 20-40 % increase of pulse repetition rate in the copper vapor laser with small tube diameters and low buffer gas pressures. The excess build up of copper metastables density is prevented by interruption ofplasma heating 3-5 ts prior the onset of a main current pulse.