Sequential frequency locking of three He-Ne lasers with one external iodine stabilizer

A laser control system is described which locks the frequencies of three He-Ne lasers (543 nm, 612 nm and 633 nm) to iodine transitions using a single external cell stabilizer. The system is fully automated and is now used at the CSIRO to provide three unmodulated frequency references for the CSIRO gauge block interferometers and for a 1 m length bar interferometer. The relative uncertainty of the three references is thought to be better than 2 × 10-10.