the figure illustrates a ring laser gyroscope which comprises a triangular block 2 exhibiting low thermal expansion . a cavity 3 is formed in the block which is defined by three reflecting corner mirrors m1 , m2 , and m3 . electrodes ( not shown ) cause gas within the cavity to form clockwise and counterclockwise monochromatic light beams , collectively indicated by reference numberal 4 , due to plasma discharge . mirrors m1 and m2 are designed to be flexible and can be moved along a direction perpendicular to their surface by conventional piezoelectric transducers t1 and t2 . the indicated applied voltages drive the piezoelectric transducers . such a transducer is disclosed in u . s . pat . no . 3 , 581 , 227 issued may 25 , 1971 . the mirror m3 permits a small amount of the radiation in the cavity to exit . these are shown as beams b1 and b2 which strike the partial reflecting mirrors m5 and m4 respectively . the partially reflecting mirrors m4 and m5 split each beam into two components , one divided toward a respective photodiode ( pd2 , pd1 ), the other towards a beam combiner m6 . the beam labeled b2 is split into beams b3 and b4 , while beam b1 is split into beams b5 and b6 . beams b4 and b5 are combined at combiner m6 to form a nearly colinear beam b7 that strikes the fringe detector fd which forms the gyro output . the principal point of this invention concerns the use of signals from beams b3 , and b6 as detected by photodetector pd1 and pd2 . the intensities of these beams are made up of a dc part and an ac part , the latter comprising the winking signals . at a constant rlg rotation rate these ac signals oscillate in time at a frequency proportional to the rotation rate . for low backscatter amplitudes the oscillations are approximately pure sinusoids . in general there is an arbitrary phase between the phases of the signals from photodetectors pd2 and pd1 ( signals w1 and w2 ). this phase can be changed by moving the mirrors m1 and m2 synchronously so that the path length of the laser cavity remains constant but the position of the beam on the mirrors changes . the preferred phase difference for minimum lock - in is 180 degrees . therefore , the control for the mirrors is set by means of the phase detectors . the detector typically includes preamplifiers 6 and 5 for respective signals w1 and w2 , the outputs of the amplifiers driving phase comparator 7 which compares the phase of signals w1 and w2 generate an output error signal ve that is zero when the phase difference between w1 and w2 is 180 degrees . these error signals will actuate the mirror driver circuit 8 such that the mirrors m1 and m2 move to reduce the error signal toward zero . the beam combining means formed by mirrors m4 , m5 and m6 and photodetectors pd1 and pd2 is different from those previously used in that it provides access to both winking signals . however , it is not the only way for obtaining both winking signals . rather than using separate mirrors , a combination of mirrors and prisms could be used . fiber optics could also be used . if the optical signals were conducted from mirror m3 toward the beam combining means , optical couplers could split a small fraction of the signals from each beam and bring them toward separate photodiodes . the signals may also be obtained through mirrors m1 or m2 by use of photodetectors appropriately located in these mirror structures . the following considers the supporting theory of the invention . the intensity of the two beams in an rlg and their phase difference is described by a system of three simultaneous , coupled differential equations as disclosed in the publications : f . aronowitz and r . j . collins , j . of applied phys . 41 , 130 ( 1970 ) and yu . l . klominontovich , et al ., soviet phys . jetp 24 , 1 ( 1967 ). a coupling between the two waves is due to backscattering of light from one beam to the other . this backscattering takes place mostly at the surface of the mirrors . the total scattering from the three mirrors is described as a single amplitude and phase shift for each beam . it can be shown that the phase shifts of the backscattering affect the lock - in as the average phase shift , where ε 1 and ε 2 are the optical phase shifts due to scattering of the first beam into the second beam and the second beam into the first beam , respectively . the lock - in band for the gyro is a function of ε and other variables including the backscatter amplitude . the theory shows that the lock - in decreases as ε approaches 90 degrees . in recent rlg computer simulations , it has been demonstrated that as ε approaches 90 degrees the phase difference between the winking signals approaches 180 degrees . no other parameters that have been tested in the simulation affect the winking signal phase difference . therefore , the phase between the winking signals should provide a measure of ε , the average backscatter phase shift and hence the winking signal phase can be used to adjust the lock - in to a minimum value . accordingly , by comparing the phase difference between the winking signals , the rlg laser path may be adjusted to minimize beam lock - in . it is noted that the concept of the present invention may be employed in dithered and non - dithered gyros . further , although the discussion is directed to a preferred embodiment employing three mirrors in a triangular housing , the invention may operate in a suitably shaped housing where more than three mirrors are mounted . it should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art .