Observation of a Sub-10-Hz Linewidth 88Sr+ 2Sr+ 21/2-2D5/2 Clock Transition at 674 nm.

In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1 s is 2.5 × 10-15. One of the lasers has been used to interrogate the 88Sr+ ²S1/2-²D5/2 transition at 674 nm, and a transition linewidth of 9 Hz has been observed. [ABSTRACT FROM AUTHOR]