Measurement of the infrared ${}^2{F}_{7/2}{-}^2{D}_{5/2}$ transition in a single ${}^{171}{\mathrm{Yb}}^{+}$ ion

The ${}^2{F}_{7/2}\mathrm{}(F=3\mathrm{})\mathrm{}{–}^2{D}_{5/2}\mathrm{}(F=2\mathrm{})\mathrm{}$ 3.43-μm transition in ${}^{171}{\mathrm{Yb}}^{+}$ has been measured to be 87 366 282 258(91) kHz. This transition is of interest as an infrared frequency standard. A subsidiary measurement of the 3.43-μm ${(F=4-F}^{\prime }=3)$ transition yields a frequency of 87 362 471 500(800) kHz. Taken with a previous measurement of the ${}^2{D}_{5/2}$ level hyperfine splitting, a ${}^2{F}_{7/2}$ level hyperfine splitting of 3620(2) MHz and an A factor of 905.0(0.5) MHz are deduced. In addition, a 3.43-μm transition isotope shift of $v_{171}–v_{172}=+4048\mathrm{}\left(4\right)\mathrm{}\mathrm{MHz}$ is obtained from these experiments and a known value for the transition in the 172 isotope. These measurements taken with previous work give a value for the ${}^2{S}_{1/2}\mathrm{}(F=0\mathrm{})\mathrm{}{–}^2{F}_{7/2}\mathrm{}(F=3\mathrm{})\mathrm{}$ electric octupole transition of 642 121 497 308(178) kHz, which will be used as a starting point in the search for this extremely weak transition.