Measurement of linear velocity using a resonant ring interferometer with a low-coherence light source

It is demonstrated theoretically and experimentally that linear velocities of reflecting objects may be measured using a resonant ring interferometer with a low-frequency light source. The limiting sensitivity of this interferometer is estimated. It is shown that a resonant ring interferometer can be used to measure extremely low linear velocities corresponding to subhertz Doppler frequency shifts of light, which cannot be measured by conventional Doppler techniques based on direct measurements of the frequency difference between the initial and reflected waves.