Algorithms for unequal-arm Michelson interferometers

A method of data acquisition and data analysis is described in which the performance of Michelson-type interferometers with unequal arms can be made nearly the same as interferometers with equal arms. The method requires a separate readout of the relative phase in each arm, made by interfering the returning beam in each arm with a fraction of the outgoing beam. Instead of throwing away the information from a single arm by subtracting it from that from the other arm, the data in one arm is first used to estimate the laser phase noise and then correct for its effect in the normal differenced interferometer data.