M.V. Chirkin, S.Y. Alekseyev, М.V. Borisov, M.A. Zakharov, V.Yu. Mishin, D.A. Morozov, A.V. Molchanov

The problem of the lock-in threshold measurement as applied to counter propagating waves in the ring laser is solved without application of precision equipment. The method developed is based on information extracting from movement of fringe pattern, which is formed by laser beams extracted from the ring cavity. The known direct least-square algorithm of ellipse fitting is used by reconstruction of Sagnac phase time series on the basis of initial quadrature signals reading. Two frequency ranges are identified in the spectrum of the generated signal. Low frequency range corresponds to the real angular velocity oscillation because of rotating unit judder. High frequency range contains the components, which reflect only of counter propagating waves coupling through laser radiation back scattering inside the ring cavity. Amplitude of filtered oscillation coincides with the lock-in threshold. The methods of band-pass filtering and synchronous detection are applied to the quantitative determination of the threshold value. The restrictions of the constant component of the angular velocity are defined that makes it possible the achievement of the correct result. The method proposed doesn-t demand fine precision of the laser rotation uniformity on application of measurements. Obtained result is insensitive to the features of current technique. Procedures of the measurement and data processing are quick and except a human factor.