As the finesse of a Fabry–Perot optical cavity increases to about 20,000, the fringe width (~10 kHz for a 50-cm cavity) is sufficiently narrow for transverse-mode splittings to be resolved by using a highly stabilized ring dye laser. A perturbative theory interprets this effect as a slight deviation of the cavity from cylindrical symmetry, the magnitude asymmetry being at the level of a few tenths of a nanometer. The understanding of these splittings will permit of accurate optical frequency measurements by the recently proposed optical–radio-frequency divider.
© 1986 Optical Society of America
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