Determination of offset between a fixed wavelength laser and an absorption line using frequency modulation spectroscopy

Frequency modulation spectroscopy is used as a new method to determine the detuning or optical frequency offset between a fixed laser line and the center of an adjacent absorption line. Because the offset is measured directly using high precision RF techniques, the accuracy is limited only by the laser linewidth. The method was demonstrated using (a) a dye laser set at a fixed frequency and an etalon resonance and (b) an infrared He-Ne laser and a methane absorption line. © 1983.