A 729 nm laser with ultra-narrow linewidth for probing 4S1/2–3D5/2 clock transition of 40Ca+

A Coherent Inc. Ti:sapphire laser MBR-110 is locked to a temperature-controlled high finesse Fabry–Perot cavity supported on an isolated platform. The linewidth is measured by locking the laser to another similar super-cavity at the same time and the heterodyne beatnote between two laser beams that locked to different cavities determines the linewidth. The result shows that the laser's linewidth is suppressed to be 41 Hz. The long-term drift is measured with a femtosecond comb and determined to be ~ 0.1 Hz/s. This laser is used to probe the 4S1/2–3D5/2 clock transition of a single 40Ca+ ion. The Zeeman components of the clock transition with a linewidth of 160 Hz have been observed.