Absolute frequency measurement of the HeNe/I-2 standard at 633 nm

The absolute frequency of a HeNe laser locked to a hyperfine component in I -127(2) is measured using a frequency standard based on a single, trapped a nd laser-cooled Sr-88(+) ion. A CO2 laser, whose frequency is measured with a Cs-based frequency chain, is used to span the frequency interval between the ion standard at 445 THz and the HeNe/I-2 laser at 474 THz. The frequen cy of the f component of the 11-5 R(127) transition of our HeNe/I-2 standar d laser is found to be 473 612 353 600 180 +/- 720 Hz at the exact operatin g conditions specified for the realization of the recommended value of this radiation. Crown Copyright (C) 2001 Published by Elsevier Science B.V. All rights reserved.