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 P-3(1) metastable state. This can have important applications in the development of quasi-CW lasers. The possibility of populating 4s4p P-1(1) and 4s5s S-3(1) states through energy pooling collisions is also investigated. The rate coefficient for pooling to the 4s5s S-3(1) state is estimated to be 10(-8)-10(-9) cm3 s-1.