I would like to hear some interpetations of what is truly going on with this description of the Sagnac effect.


"Stedman: The Sagnac effect in a ring laser is the frequency difference that arises between counterrotating modes when the whole system is rotating. The co-rotating mode shifts to the red, the counterrotating mode to the blue. Measuring the frequency difference gives the rotation rate. The frequency difference is also the beat frequency."

"Figure 2. Sagnac effect in ring laser. The standing wave, S, in a ring laser remains stationary with respect to the fixed stars, even though the cavity of the ring laser, designated as the frame F, rotates along with the earth. An opening, D, for the detector, allows S to be observed. If F rotates, D sees beats that are l/2 apart."


"Bilger: The two counterrotating beams form a standing-wave pattern in inertial space (Figure 2), enclosed and defined by the geometry of the mirrors involved. Imagine an ideal circle of radius R. At the point D, a detector is placed that looks at the standing-wave pattern. If now the frame F, which is the cavity, is rotated, the necklace stands still in inertial space (i.e., with respect to the fixed stars), and therefore the detector moves by the pattern, sensing the minima-maxima by producing a beat frequency."

http://www.spie.org/app/publications...ep96/gyro.html



Inertial frame means with respect to the stars or absolute.

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