Comparison of 127I2-stabilized frequency-doubled Nd:YAG lasers at the Bureau International des Poids et Mesures.

A frequency comparison was carried out between iodine-stabilized Nd:YAG lasers at 532 nm from the Bureau International des Poids et Mesures, the Centre for Metrology and Accreditation, the Czech Metrology Institute, and the Bureau National de Metrologie-Institut National de Metrologie. The frequency differences between lasers, as well as the frequency reproducibility of each system, were investigated. Pressure-, modulation-, and power-induced shifts were studied. A frequency dispersion (1 σ) of 3.5 kHz (6.2 × 10-12 in relative terms) with an average reproducibility for each laser of the order of 0.4 kHz (7.1 × 10-13 in relative terms) was observed over the duration of the comparison. Relative stabilities better than 1 × 10-13 at 1 s were demonstrated for the third-harmonic systems.