Simple scheme for tunable frequency offset locking of two lasers

We present a scheme for stabilizing the difference frequency of two indepen dent 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-freque ncy domain (100 MHz-10 GHz) can be controlled with long-term stability of b etter than 1 MHz. (C) 1999 American Institute of Physics. [S0034-6748(99)00 201-4].