Simple scheme for tunable frequency offset locking of two lasers

We present a scheme for stabilizing the difference frequency of two independent lasers. The scheme is based on simple electronics and makes use of the frequency-dependent phase shift experienced by a signal when it propagates through a delay line of coaxial cable. The stabilized difference frequency can be tuned over a wide range. Difference frequencies in the radio-frequency domain (100 MHz–10 GHz) can be controlled with long-term stability of better than 1 MHz.