Abstract
Improvements in the frequency stability of the visible helium-neon laser are possible using saturated absorption in iodine vapour. Recent improvements in the design of these lasers are discussed, and the importance of third derivative locking methods in realizing the possible high reproducibility of the iodine reference frequencies is emphasized. Allan Variance measurements of the beat frequency between two stabilized lasers indicate a long term stability of better than 1 part in 1010.