Plasma parameters and pumping mechanism in a helium-cadmium laser

The dominant pumping mechanism of the 441.6 nm Cd II line in a three-colour hollow-cathode discharge laser

“…When the density of cadmium atoms increases to 10 15 cm −3 , or higher, the second term in the denominator of ( 14) becomes essentially larger than the first one (Kalinchenko et al 1989). This is possible since radiative resonance transitions to the ground state of the He atom (the shunting Penning process) are 'closed' (Ivanov et al 1972) and both upper excited states and metastable ones take part in the Penning process. Therefore, for the radial dependence of W p (r) in this case we have (Inaba et al 1981).…”

“…The pumping mechanism of this line in a HCD is being discussed. Comprehensive studies of the 441.6 nm line for PC were reported in papers by Silfvast (1968Silfvast ( , 1969, Ivanov et al (1972), Browne and Dunn (1973), Mizeraczyk (1975), Csillag et al (1971), Mori et al (1978) and Boulmer-Leborgne et al (1987) with three most probable processes found; namely the Penning process He * + Cd 0 → He 0 + Cd + * ( 2 D * 5/2 ) + e (1a) The pumping rates in these reactions can be written as follows:…”

“…One of the most convincing experiments to confirm the dominant contribution of the Penning process to the excitation of the 441.6 nm laser line in a PC is the direct optical pumping of a PC plasma by helium lamp radiation (Ivanov et al 1972). When the resonant transitions of helium are blocked, the lamp radiation leads to a transfer of helium atoms from metastable to highly excited states and therefore to the growth of the pumping rate and laser output power.…”