Initial Condition and Cooling Time of Recombining Helium Plasma for Stationary VUV Lasing Action

Abstract

Calculated optimum conditions as to initial electron density and cooling rate of a recombining helium plasma for the production of VUV laser oscillation of the Hell 164 nm line are presented together with an explanation of the population inversion mechanism. For high initial plasma density (~1018 cm-3) rapid cooling (τE ≦10-13 sec) should produce a short pulse laser oscillation. For medium initial density (~ 10-16 cm-3), stationary laser oscillation can be produced by much slower cooling (τE ~ 10-8 sec) but on cooling with τE > 10-7 sec the oscillation can hardly be realized. For lower initial plasma density ( ≦ 1015 cm-3), laser oscillation is not possible because the population inversion obtained is not sufficient.