Self-broadening of optical double resonance lines in cadmium

TLDR: In this article, a method is developed for calculating the cross section for line broadening in the limiting case in which important collisions may be considered to occur very rapidly with respect to the periods corresponding to the transitions in question.

Abstract: Collision broadening studies were made of optical double resonance lines in cadmium. The results indicate that the DELETE ABSTRACT 18574. A method is developed for calculating the cross section for line broadening in the limiting case in which important collisions may be considered to occur very rapidly with respect to the periods corresponding to the transitions in question. This method is essentially an extension of the familiar sudden approximation; reference is made throughout to the particular example of optical double resonance only for definiteness and because there are available experimental results for comparison with the theory. Assuming the impact model and considering the case when the energy levels in question are well resolved with respect to their width, an exact expression is found for resonant selfbroadening in the usual weak r-f field limit of interest in double resonance. For the case of very small oscillator strengths for the optical transition (intercombination lines), the resonant broadening becomes sufficiently small so that second-order, intermediate-state processes dominate, and approximations must be made to effect sums over intermediate states. Here the broadening is of the same sort as foreign gas broadening, and in many cases of interest, the approximations can be made in amore » sufficientiy realistic manner to obtain useful expressions for the broadening. It is shown that the resonant cross section and this secondorder cross section are not additive, but that the one that is larger dominates the total cross sections very strongly. The self-broadening and foreign gas broadening (by the noble gases) of double resonance lines in the group II metals and the self-broadening in the optical spectrum of helium are evaluated. In all cases the theoretical predictions are in good agreement with measurements. (auth)« less