Measurements of optical frequencies from the infrared to the visible

We have built an optical frequency synthesis chain starting from our laboratory-measured reference at 29 THz (CO2/OsO4 laser) and we have measured the frequency of a He-Ne laser locked on a hyperfine transition of iodine at 473 THz. The result of the measurement of the laser locked on the 'f' component of the (127)R11-5 transition is 473,612,353,586.9 +/- 5 kHz. The measurement uncertainty is 10 times better than that of the previous published measurement. It is only limited by the reproducibility of the standard laser. Our chain is potentially capable of measuring optical frequencies from the visible down to the near IR range with an accuracy level of 10-12, which is presently limited by our reference accuracy.