Laser-frequency stabilization using mode interference from a reflecting reference interferometer

We present a new method for locking the frequency of a laser to a reference-interferometer cavity. For a nonmode-matched input beam, the light reflected off a cavity contains an interference between the wave fronts corresponding to the various cavity modes. A detector placed at the proper position on the interference pattern provides a signal proportional to the imaginary component of the reflected field. As a function of laser frequency, this signal is dispersion shaped and can be used as the error signal for electronic frequency stabilization.