A fundamental limit to the sensitivity of optical interferometry is thermal noise that drives fluctuations in the positions of the surfaces of the interferometer's mirrors, and thereby in the phase of the intracavity field. A scheme for substantially reducing this thermally driven phase noise is provided in which the strain-induced phase shift from a mirror's optical coating cancels that due to the concomitant motion of the substrate's surface. As such, although the position of the physical surface may fluctuate, the optical phase upon reflection can be largely insensitive to this motion.