It is demonstrated that the optogalvanic effect in a sodium hollow cathode discharge is a sensitive detector specific to the intracavity absorption of sodium atoms in a flame. In this feasibility study the variation of the optogalvanic signal vs the sodium concentration in the flame indicated a detection limit below 1 ng/ml. The sensitivity can be easily improved, and this technique is applicable to other atoms and Doppler-free intermodulation spectroscopic detection methods.
Edward F. Zalewski, Richard A. Keller, and Charles T. Apel, "Optogalvanic effect as a detector for intracavity atomic absorption in a cw dye laser," Appl. Opt. 20, 1584-1587 (1981)