Iodine-stabilized frequency-doubled Nd:YAG lasers at λ=532 nm: design and performance

Abstract

Three independent iodine stabilized laser systems have been set-up at the Physikalisch-Technische Bundesanstalt (PTB) for applications in frequency- and dimensional metrology. The lasers use saturated absorption of the P(54) 32 - 0 iodine transition in an external iodine cell as a frequency reference. The signals for stabilizing the lasers are obtained by using wavelength modulation spectroscopy and frequency modulation spectroscopy, respectively. With the different setups we have achieved instabilities of < 2 (DOT) 10<SUP>-13</SUP> for an integration time of 1 s and an agreement of the stabilized laser frequencies of the individual systems to better than 3 kHz. Together with absolute frequency measurements performed recently these lasers can compete with optical frequency standards based on atoms or ions. The drawbacks and advantages of the individual set-ups are discussed with respect to frequency stability, reproducibility and uncertainty. Besides the reproducibility, impurities of the iodine cells limit the uncertainty of the stabilized frequency. We ave used one of our systems to investigate a random sample of iodine cells and compared these results with the ones obtained with an iodine-stabilized HeNe laser.