Information on laser gyros:

A laser gyro is a ring laser which means that it has 2 laser counter-propagating

beams traveling in a closed path (ring). Because each beam has equal intensity, it forms regions of high electromagnetic field energy density called antinodes. Since both beams usually travel at the same speed, these antinodes stand still in the frame of the laser gyro. However, when the laser gyro rotates, the beam going in the direction of rotation travels slower with respect to the laser gyro frame and the opposite beam travels faster. That causes the antinodes to slip backward instead of keeping up with the frame rotation. For a square laser gyro as shown here, the number of antinodes that pass a given point in the frame during a complete rotation of the laser gyro frame is governed by the simple equation,

where N is the total number of antinodes in the laser. Since I have chosen to depict 60 antinodes in this laser gyro frame, I expect to have about 47 antinodes passing a given point (for example, the point could be a photo-detector) during a complete rotation of the ring. I have chosen to make one of the antinodes black and one of the mirrors red so that the viewer can easily see how far the antinodes progress during a single rotation of the laser gyro frame.