Direct frequency measurement of the I₂-stabilized He–Ne 473-THz (633-nm) laser

The absolute frequency of the 473-THz He-Ne laser (633 nm), stabilized on the g or i hyperfine component of the (127)I(2) 11-5 R(127) transition, was measured by comparing its frequency with a known frequency synthesized by summing the radiation from three lasers in a He-Ne plasma. The three lasers were (1) the 88-THz CH(4)-stabilized He-Ne laser (3.39 microm), (2) a 125-THz color-center laser (2.39 microm) with its frequency referenced to the R(II)(26) (13)C(18)O(2)laser, and (3) the 260-THz He-Ne laser (1.15 microm) referenced to an I(2)-stabilized dye laser at 520 THz (576 nm). The measured frequencies are 473 612 340.492 and 473 612 214.789 MHz for the g and i hyperfine components, respectively, with a total uncertainty of 1.6 parts in 10(10). The frequency of the i component adjusted to the operating conditions recommended by the Bureau International des Poids et Mesures is 473 612 214.830 +/- 0.074 MHz.