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 $88.4\hspace{0.5em}\mathrm{THz}$ $\left(3.39\mathrm{}\hspace{0.5em}\mu \mathrm{m}\right).\mathrm{}$ A frequency mismatch of $1.78\hspace{0.5em}\mathrm{THz}$ between $4\times 88.4\hspace{0.5em}\mathrm{THz}=354\mathrm{}\hspace{0.5em}\mathrm{THz}$ and the $D_2$ line was bridged with an optical frequency comb generator. We find $f_{D2\mathrm{}}=351\mathrm{}725718.50\left(11\right)\mathrm{}\hspace{0.5em}\mathrm{MHz}$ for the hyperfine centroid, improving previous results by almost two orders of magnitude.