Optical frequency standard at 532 nm

We have constructed a frequency-doubled Nd:YAG laser source stabilized via modulation transfer spectroscopy to hyperfine absorption peaks in molecular iodine. The system is suitable for use as an optical frequency standard because of the excellent stability (σ<1×10^-13 for τ⩾1 s) and reproducibility (75 Hz per ir laser) observed between two independent dissimilar systems. With heterodyne techniques, we have measured the hyperfine splittings of seven rovibrational transitions in ¹²⁷I₂. A computer fits the data for the hyperfine coupling constants based on a four term Hamiltonian. The residuals from these fits have a standard deviation as low as 520 Hz, displaying the best reported agreement to date with the quadrupolar hyperfine Hamiltonian. Modulation transfer lineshapes have been accurately recorded using rf offset phase-locking techniques with our two systems. Pressure shift (-1.3 kHz/Pa) and broadening (74 kHz/Pa) of the a₁ component of R(56)32-0 have been derived from these lineshape measurements