Investigation of backscattering effects on the correlation properties of a He–Ne ring laser

By making provisions for retroreflecting the two emerging counterrotating waves back into the laser cavity with variable amplitudes and phases, we have investigated backscattering effects in a He–Ne ring laser. In particular, we have measured the intensity flucuations and the intensity cross correlation between the two counterpropagating modes as the pump parameter and the phase of the backscattering are varied. We confirm the prediction based on third-order laser theory that equal-time moments depend on backscattering only through the combination R1 + R2*, where R1 and R2 are complex backscattering coefficients. Good agreement between experiment and third-order laser theory is obtained so long as the normalized pump parameter is below approximately 100.