Progress in stabilization of the He-Ne/127I2 wavelength standard at 633 nm and results of an international comparison between the PTB and the UME

Abstract

A detailed description of the He-Ne/127I2 laser wavelength standards developed at the National Metrology Institute of Turkey (UME), using high-frequency modulation and featuring a long-term relative instability of a few parts in 1014, is presented. The frequency dependence of the lasers on the iodine gas pressure, modulation width and saturating field intensity have been studied with a very low uncertainty level, and the common effect of these parameters on the output frequency has been demonstrated. A new method of accurately measuring modulation width has been realized, making an important contribution to the improvement of reproducibility of this type of wavelength standard. An international comparison between the laser standards of the Physikalisch-Technische Bundesanstalt (PTB) and the UME has been performed. Several iodine cells studied in a laser with an accurate servo-system, reveal a correlation between the spacing of the molecular resonances, the gas contamination in the iodine cell, and the output frequencies of the laser when locked to different iodine components.