Diode-pumped Yb-doped fluoride lasers widely tunable around 1.03 μm

In this paper, cw diode-pumped Yb-doped fluoride lasers, based on KYF4 and LiYF4 active crystals, are reported with wavelength tunability ranges wider than 55 nm. The V-shaped laser cavity used in the laser experiments is composed by a high-reflectivity (HR) plane mirror, a HR curved mirror and a plane output coupler. The laser crystal is placed at Brewster angle close to the input mirror and is longitudinally pumped by a cw fiber-coupled diode providing a maximum output power of 2.6 W in a 50 mum core diameter multimode fiber at 970plusmn2 nm for a temperature of 25°C. The pump beam is collimated and then focused into the active crystal through the input mirror using a pair of anti-reflection coated plano-convex lenses. To tune the laser emission wavelength, a birefringent filter with a free-spectral range of ˜65 nm, based on 2-mm thick quartz plate with the optical axis lying on the crystal plane, is inserted at Brewster angle in the longest arm of the resonator. It is concluded that the KYF4 laser shows a maximum output power of 490 mW and a slope efficiency of 31%, whereas the performance of the LiYF4 laser is characterized by a maximum output power and a slope efficiency of 360 mW and 24%, respectively.