Collisional recycling of excited atomic populations in ca in a thermionic diode following pulsed-laser excitation of a metastable state

Experimental results are reported where the rates of collisional energy transfer in optically prepared atomic metastable states are considerable compared with the rate of normal radiative decay. A remarkable consequence is a large increase in the effective lifetime of some excited states lying above the optically prepared state. The specific case of calcium is presented here as an example where over a 1000-fold increase in the lifetime of 4s3d ³D states has been experimentally measured following pulsed-laser pumping of 4s4p ³P₁ metastable state. This can have important applications in the development of quasi-CW lasers. The possibility of populating 4s4p ¹P₁ and 4s5s ³S₁ states through energy pooling collisions is also investigated. The rate coefficient for pooling to the 4s5s ³S₁ state is estimated to be 10^-8-10^-9 cm³ s^-1.