Excitation mechanisms in CW He-Hg lasers

The collision processes responsible for populating and de-populating upper and lower levels of the cw He-Hg ion laser are investigated using flowing afterglow techniques. It is shown that the superior performance of the laser at 6150 Å compared to that at 7945 Å is not due to a difference in excitation mechanism — both are excited by charge transfer from He⁺ — but instead reflects a greater effectiveness of second kind collisions of electrons in depopulating the 7p²P_{$\text{1}\text{2}$} upper level of the 7945 Å transition. The charge transfer, excitation rate constants for several Hg II levels are compared, and values for the rate constant for the electron collision de-excitation process are deduced.