Measurement of the frequency fluctuations of a ring laser

An electron-counting frequency meter was used to measure the dependence of the phase advance of the difference frequency of a ring laser on the averaging time (5.4 microsec to 2 sec). The results are compared with the measured spectral power density of frequency fluctuations in the 0.25 Hz to 100 kHz range. It is concluded that, when all possible errors are carefully taken into account, the proposed method for measuring phase-advance dispersion makes it possible to determine the frequency fluctuations of a ring laser in a wide spectral range.