Effect of SiO2 on the Stark splitting enlargement of Yb3+ in phosphate glass

Abstract

Up to now, high-energy large-scale Yb3+ laser has still faced to the fact that no proper gain media are available, though researchers made a more than ten year effort for it. Yb: fluorophosphate glass is the only material used in a laser system, reaching an output of more than 10 TW. As is well known, the thermal blocking of Yb3+ laser is a bottleneck in laser operation, which is closely related to the Stark splitting of Yb3+ in a gain medium. Conventional Yb: phosphate glass has the advantages in Yb3+ concentration, lifetime and cross section over silicate glass, however, its small Stark splitting is the main drawback that induces difficulties in realizing laser output at room temperature. Yb: phosphate glass will be a good gain medium for high power Yb3+ laser if the Stark splitting is improved. This study focuses on the enlargement of the Yb3+ Stark splitting in phosphate glass by introducing SiO2, thereby achieving a large Stark splitting property compared with the phosphate glass. The glass 60P2O5-7.5Al2O3-15K2O-17.5BaO-1Yb2O3 is used as the base glass, and the modified glass denoted as PS is obtained by doping a certain amount of SiO2. Such a glass is prepared by the conventional melting-quenching method. Lorentz fitting is performed to the absorption and fluorescence spectra for determining the Stark splitting scheme. Raman spectrum is used for the auxiliary judgment of the attributions of the different spectroscopic bands. Then the results are confirmed by the barycenter law of Yb3+ ion. Investigations show that the addition of SiO2 can enlarge the Stark splitting obviously from the original 670 to 771 cm-1 in PS3. Scalar crystal field parameter N_{J} and asymmetry degree around Yb3+ are also increased due to SiO2 incorporation. Meanwhile, spectroscopic properties of PS series glasses, such as fluorescence effective line width (Δλeff) and fluorescence lifetime (τf), are moderately enhanced. The glass transition temperature is improved greatly, which is very valuable for high power Yb3+ laser. These results suggest that the introduction of a second network former is an effective way to enlarge the Stark splitting of Yb3+ in phosphate glass. Next, our investigation will focus on preparing the high-homogeneity SiO2 modified phosphate glasses and the corresponding laser experiments.