Development and evaluation of a 532 nm iodine-stabilized laser frequency standard at PGMF

Abstract This work presents the development and evaluation of a 532 nm iodine-stabilized laser frequency standard at the National Precise Gravity Measurement Facility (PGMF) in China. The 532 nm laser serves as the length reference for high precision absolute gravimeters that are developed at PGMF. The absolute frequency measurement of the hyperfine transition R(56)32-0:a 10 line of the molecular iodine at 532 nm is extensively performed. The absolute frequency measurement is carried out through an optical frequency comb, which is referenced to a hydrogen maser. The maser output frequency is calibrated by a local time-scale system, which is traced to the Coordinated Universal Time. To verify the measurement reliability of the optical frequency comb, an acetylene-stabilized laser from the National Institute of Metrology of China (NIM) is employed as the frequency transfer standard. The major noise contributions are studied, and the uncertainty of the 532 nm laser system is evaluated. The absolute frequency of the laser locked to the molecular iodine R (56) 32-0: a 10 hyperfine transition line is measured to be 563 260 223 515.0 kHz, with a total uncertainty of 5.1 kHz. The frequency instability of the laser is measured to be about 3 × 10 −13 / τ 1/2 over the averaging time of 1 s–100 s. These results are consistent with previous international findings. This study thus will support and validate the traceability of gravity measurements at PGMF to the SI units.