Abstract. A frequency comparison was carried out of iodine-stabilized Nd:YAG lasers from the Bureau International des Poids et Mesures (BIPM), the National Research Laboratory of Metrology (NRLM, Japan, now the National Metrology Institute of Japan, NMIJ) and the Bureau National de Métrologie-Institut National de Métrologie (BNM-INM, France). Frequency reproducibility between lasers as well as for each system was investigated. Pressure- and modulation-induced frequency shifts were studied. A frequency dispersion (1 σ) of 1500 Hz (2.6 × 10⁻¹² in relative terms) with an average reproducibility of 250 Hz (4.3 × 10⁻¹³ in relative terms) was observed over the duration of the comparison. Results of stability measurements are given. Those obtained with the third-harmonic technique are especially encouraging in view of its performance and relative simplicity.

Print publication: Issue 6 (December 2001)