Spectroscopic measurements of the electric-quadrupole-allowed 5$d^{10}$6s ${\mathrm{}}^2$$S_{1/2}$ to 5$d^9$6$s^2$ ${\mathrm{}}^2$$D_{5/2}$ transition near 282 nm on a single, laser-cooled ${\mathrm{Hg}}^{+}$ ion give a recoil-free absorption line (carrier) and well-resolved motional sidebands. From the intensity ratio of the sidebands to the carrier, the effective temperature of the ${\mathrm{Hg}}^{+}$ ion was determined to be near the theoretical minimum of 1.7 mK. A fractional resolution of better than 3×${10}^{\mathrm{-}11}$ for this ultraviolet transition is achieved.

• Received 13 April 1987

DOI:https://doi.org/10.1103/PhysRevA.36.428