The hyperfine structure of the ${}^{2}{S}_{1/2}{\ensuremath{-}}^{2}{D}_{5/2}$ quadrupole transition at 674 nm in
87Sr+ has been observed. The ion was confined in a Paul trap and cooled using laser radiation at 422 and 1092 nm. The quadrupole transition was observed by monitoring quantum jumps in the 422-nm fluorescence. The odd isotope of strontium has ``clock'' transitions independent of the first-order Zeeman shift and the
2D5/2 state hyperfine structure constants have been determined as
AD5/2=2.1743(14)MHz and
BD5/2=49.11(6)MHz. Standard uncertainties have been added in parentheses. These values allow the second-order Zeeman shifts to be calculated. The ${}^{88}{\mathrm{Sr}}^{+}{\ensuremath{-}}^{87}{\mathrm{Sr}}^{+}$ isotope shift for the 674-nm quadrupole transition has been measured to be 247.99(4) MHz.
Stabilization of a laser to an optical-clock transition has been demonstrated using Ramsey's phase-modulation technique. The technique was implemented using a 674 nm laser and a component of the 5 s 2S1/2 → 4d 2D5/2 optical clock transition in a single 88Sr+ ion. The lock performance observed was consistent with the short-term stability of the local oscillator. Compared with existing frequency-modulation stabilization schemes, this technique offers advantages for use in single-ion optical clocks through its possible increased resolution and the ability to conveniently compensate known systematic shifts.