A simple frequency discriminator circuit for offset locking of lasers

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Abstract
Describes a frequency-lock circuit. The components used are readily available and the circuit can be easily reproduced. The design gives a fast loop response and large capture range, thus making it ideal for locking potentially noisy laser systems. In addition it is free from the problems of drift often associated with frequency-locked circuits. The authors have used the design to offset-lock two carbon dioxide lasers giving a resultant beat note only 500 Hz wide. The quality of the lock is independent of the size of the offset while the technique is adaptable to lasers in all parts of the spectrum, being limited only by the response of a suitable beat detector.