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

Abstract

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.