725  nm watt-level injection-locked continuous-wave Ti:sapphire laser for a mercury optical lattice clock

We develop a watt-level 725 nm continuous-wave tunable narrow linewidth injection-locked Ti:sapphire laser. The seed laser is frequency-locked on a Fabry-Perot cavity to narrow the linewidth and stabilize the frequency. Because the wavelength of the seed laser is located at the edge of the gain profile of the Ti:sapphire crystal, it is difficult to injection-lock the Ti:sapphire laser at 725 nm. A cavity mirror, which has a long-pass-filter coating with a sharp edge, is used in the Ti:sapphire cavity to suppress mode competition from the long wavelength side. This method effectively reduces the power requirement of the seed laser at 725 nm, and the Ti:sapphire laser can be injection-locked at higher output power. As a result, a 1 W output power with a 27% slope efficiency is achieved in the injection-locked laser, and a 210 mW UV laser is obtained in a subsequent second-harmonic generation stage. To the best of our knowledge, this is the shortest wavelength for the watt-level injection-locked continuous-wave Ti:sapphire laser. This laser will be used in a mercury optical lattice clock in the future.