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⋅10 -13 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 [ 1,2 ] 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 have 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.

A continuously scanning separate-crystal single-photon x-ray interferometer

“…The frequencies f r,m are obtained from the respective +1st order of two acousto-optical modulators (AOM) and then coupled into the respective fibers which are fed through the vacuum chamber into the interferometer setup. The laser source, a frequency-doubled Nd:YAG laser [36,37], the AOM, and the fiber-coupling are on a separate optical table in a different room. It is worth noting that the first beam splitting appears on this table.…”

Ultrastable metrology laser at 633 nm using an optical frequency comb

“…Following that, the metrological frames of such laser wavelength standards operating at national metrology institutes are mainly built up with ultra-low expansion materials, such as Zerodur ® [22], Invar ® [18,23] or Super-Invar ® [10]. Because metrology He-Ne lasers emit less than 1.5 mW on a single mode, only a small optical power can be used for its stabilization in comparison to a solid state laser systems with up to 100 mW [24]. That is the reason why the iodine absorption cell is not part of a separated control loop and has to be integrated in an intracavity fashion, where an intracavity beam power of 10 ± 5mW is guaranteed.…”

A heterodyne interferometer with periodic nonlinearities smaller than ±10 pm

“…The light was split into two parts: one was used to feed the interferometer optics and the other one used for the Doppler-free iodine frequency stabilization of the laser. Using frequency modulation spectroscopy, the laser was locked to the first hyperfine structure of the line P54 (32-0) [14]. This is achieved by controlling the temperature of the YAG crystal through the pump diode current (slow loop) and the resonator length by a piezoelectric crystal (fast loop).…”