Dependence of laser radiant power on electron concentration in a He-Ne plasma

Abstract

1. In a tube of diameter 4 mm with a He—Ne mixture, a decrease was observed in the vhf resonator shift (decrease in the plasma electron concentration) with increase of discharge current, beginning at a certain current value. Possible causes are: a) an increase of electron temperature with increase in discharge current because of rarefaction of the gas in the small diameter tube; b) the appearance of groups of fast electrons with increase of current; c) the appearance of current instabilities, confirmed by the generation of low-frequency noise. 2. The appearance of induced emission at λ=3.39 μ is accompanied by a noticeable increase in the vhf resonator frequency shift (by an increase in plasma electron concentration). The cause may be photoionization of excited neon atoms, including cascade ionization. 3. The dependence of the radiant power at λ = 0.6328 μ on the discharge current (in the absence of lasing at λ = 3.39 μ) follows that of ne(Id). Therefore, the decrease of radiant power with increase of discharge current, beginning at a definite value of ne, cannot be explained by increase of the population of the lower operating 2p4 neon level. Evidently, this decrease is due to a decrease in the population of the upper operating 3s2 neon level because of the fall in ne, or the electron temperature plays a more substantial part here than does variation of ne.