Laser offset-frequency locking using a frequency-to-voltage converter

Abstract

Many applications of lasers in research and industry require that a slave laser can be frequency locked at some selectable offset frequency from a stable reference laser. Conventionally an optical phase lock circuit has been used to provide this frequency lock. In some applications there is no requirement to ensure phase coherency between the two lasers, and in these cases, the high bandwidth requirements of a phase-locked loop make the circuit much more complicated than necessary. We describe a much simpler frequency-locking circuit, based on a commercial frequency-to-voltage converter, which is capable of reducing frequency fluctuations between the lasers to less than 400 Hz for time scales longer than 0.1 s.