Multi-input digital frequency stabilization of monolithic lasers

Abstract

A digital control application for the frequency stabilization of optical frequency standards is presented. The standard employed is a monolithic neodymium in yttrium aluminum garnet laser locked to an iodine frequency reference. Traditionally, laser frequency is locked to the reference through analogue loops, which may require a lengthy set-up and a manual search for the reference to which to lock the source. Digital control avoids these steps and provides complete and robust instrument automation. The theory and results of a Digital Control Unit (DCU) designed to improve and facilitate stability set-up and performance are presented. The DCU elaborates frequency error signal between laser and reference at 10 kHz so as to co-ordinate a set of three frequency actuators (temperature servo, piezo-electric ceramics, acousto-optic modulator) capable of compensating frequency drifts below 1 part per 10 12 under normal environmental conditions.