Characteristics of four-wave operation of a single-isotope He — Ne ring laser with linear and circular wave polarisations

An experimental investigation was made of the characteristics features of four-wave operation of a single-isotope He — Ne ring laser (λ = 1.15 μm) with orthogonal linear and circular polarisations of waves at frequencies differing by half the intermode spacing. Four-wave operation with orthogonal circularly polarised waves was observed in a fairly narrow range of the cavity length detuning and, as a rule, was characterised by self-oscillations of the intensities of all four waves. Four-wave operation with orthogonal linearly polarised waves was found in a wide range of the detuning and of the excess of the gain above the losses.