A 1.5-W frequency-doubled semiconductor disk laser tunable over 40 nm at around 745 nm

We report on a semiconductor disk laser emitting 1.5 W of output power at the wavelength of 745 nm via intracavity frequency doubling. The high power level and the >40 nm tuning range make the laser a promising tool for medical treatments that rely on photosensitizing agents and biomarkers in the transmission window of tissue between 700 and 800 nm. The InP-based gain structure of the laser was wafer-fused with a GaAs-based bottom mirror and thermally managed with an intracavity diamond heat spreader. The structure was pumped with commercial low-cost 980 nm laser diode modules. Laser emission at 1490 nm was frequency-doubled with a bismuth borate crystal that was cut for type I critical phase matching. At the maximum output power, we achieved an optical-to-optical efficiency of 8.3% with beam quality parameter M2 below 1.5. The laser wavelength could be tuned with an intracavity birefringent plate from 720 to 764 nm.