Experimental study of difference-frequency fluctuations of a ring laser in the double-mode regime

The natural frequency fluctuations (NFF) of ring lasers operating in the double-mode regime at a wavelength of 0.63 micron were measured. It is shown that, in double-mode operation, the NFF speactrum at low frequency has a Lorentz form, which is most pronounced at the limit where the double-mode regime arises. In the case of the appearance of the double-mode regime in precision devices based on ring lasers, this can have a substantial influence on the error for averaging times of about 2 ms.