Absolute optical frequency measurement of the cesium D-2 line

We have performed an absolute optical frequency measurement of the cesium D-2 line at 352 THz (852 nm). This frequency is an important scaling parameter in atomic interferometry: The D-2 line has been compared with the fourth harmonic of a methane stabilized He-Ne laser at 88.4 THz (3.39. mu m). A frequency mismatch of 1.78 THz between 4 X 88.4 THz=354 THz and the D-2 line was bridged with an optical frequency comb generator. We find f(D2)=351 725 718.50(11) MHz for the hyperfine centroid, improving previous results by almost two orders of magnitude.