Comparison between the He-Ne laser wavelength standards at 633 nm from the UME and the BIPM

An international comparison of the I-127(2) stabilized lasers, uses as wavelength standards and belonging to the National Metrology Institute of Turkey (UME) and the Bureau des Poids et Mesures (BIPM), has been performed at the BIPM. A frequency stability of 45 Hz (a standard deviation for a series of measurements over four days at an averaging time of about one hour), or 1 part in 10(13), has been achieved. This indicates significant progress in the stabilization of this type of frequency standard and establishes a new level for international comparisons at 633 nm. The frequency difference between the UME and the BIPM standards, which incorporate quite different laser components and iodine cells, has been found to be 0.7 kHz, much smaller than the reproducibility usually reported for this kind of laser standard. For the portable UME standard, the difference in frequencies found before and after the comparison, when measured against a stationary UME laser, was less than 3 x 10(-13).