Natural fluctuations of the difference between the frequencies of opposite waves in a ring laser

An experimental investigation was made of natural fluctuations of the difference between the frequencies of opposite waves in an He–Ne ring laser emitting at the wavelength of 1.15 µ when the excess over the lasing threshold was up to a factor of 2.5. The dependences of the spectral density of these fluctuations on the output power were determined when this power was varied by introducing the losses into the resonator or by altering the pumping rate. The experimental results were in good agreement with a phenomenological theory. The nature of saturation of the active medium was also determined: it differed from the usually assumed approximation for an inhomogeneously broadened gain profile.