Use of plasma tube impedance variations to frequency stabilize a CO2laser

A method for stabilizing the frequency of a single-
J
- value CO
2
laser to the center of its output power versus frequency curve based upon the variation of the impedance of the plasma tube with the optical power extracted is described. Frequency modulation of the laser produces an ac component of voltage drop across the plasma tube, which is synchronously detected to generate a frequency-error signal.