Single-frequency IR and visible lasers are of a great interest in many research and application fields. We present in this paper, what we believe to be, to the best of our knowledge, the first diode-pumped Ytterbium-doped solid-state laser emitting at 1003.4 nm in single-frequency operation and first results obtained in the blue-green region by second harmonic generation (SHG).
The laser is based on an diode-pumped Yb:YSO (Yb:Y2SiO5) crystal. The choice of an Yb-doped crystal, pumped at 978 nm, involves two main constraints. First, the small difference, between pump and laser wavelengths, prevents the use of suitable standard dichroic mirrors. Secondly, due to the quasi-three level transition, reabsorption is significant around 1 μm and pump-absorption has to be highly saturated all along the crystal length.
The pump source is a single-emitter laser diode providing a maximum power of 4 W at 978 nm. The resonator is a six-mirror ring-cavity containing a Faraday rotator to obtain unidirectional operation. A thin Fabry-Perot etalon at Brewster angle is used to maintain linear polarization as well as finely tune the laser wavelength.
More than 300 mW of single-frequency radiation at 1003.4 nm has been obtained for 3.2 W of incident pump power. First intracavity SHG results are also presented using a KNbO3 nonlinear crystal at 76.5 °C to operate in non-critical phase-matching. In this configuration, 300 mW of IR radiation and 14 mW of aquamarine wavelength (501.7 nm) have simultaneously been obtained at room temperature in single-frequency operation.