Structural, spectroscopic, and tunable laser properties ofYb3+-dopedNaGd(WO4)2

Abstract

the two nonequivalent 2b and 2d sites of the I4 ¯ structure, but Yb 3+ and Gd 3+ ions are found preferentially in the 2b site. Optical spectroscopy at low 5K temperature provides additional evidence of the existence of these two sites contributing to the line broadening. The comparison with the 2 F7/2n and 2 F5/2n Stark energy levels calculated using the crystallographic Yb-O bond distances allows to correlate the experimental optical bands with the 2b and 2d sites. As a novel uniaxial laser host for Yb 3+ , NaGdWO42 is characterized also with respect to its transparency, band-edge, refractive indices, and main optical phonons. Continuous-wave Yb 3+ -laser operation is studied at room temperature both under Ti:sapphire and diode laser pumping. A maximum slope efficiency of 77% with respect to the absorbed power is achieved for the polarization by Ti:sapphire laser pumping in a three-mirror cavity with Brewster geometry. The emission is tunable in the 1014– 1079 nm spectral range with an intracavity Lyot filter. Passive mode locking of this laser produces 120 fs long pulses at 1037.5 nm with an average power of 360 mW at 97 MHz repetition rate. Using uncoated samples of Yb: NaGdWO42 at normal incidence in simple two-mirror cavities, output powers as high as 1.45 W and slope efficiencies as high as 51% are achieved with different diode laser pump sources.