Comparative study on the spectroscopic and laser propertiesof mixed vanadates Ybt:Y x Gd1-t-x VO4with different compositions

The room-temperature polarized absorption and emission spectra of Yb doped mixed vanadates Yb0.005:Y0.298Gd0.697VO4, Yb0.007:Y0.407Gd0.586VO4, and Yb0.009:Y0.575Gd0.416VO4 have been studied. The results show that the strongest absorption and emission, occurring at wavelength of 985 nm, correspond to the π polarization, depending on the composition the maximum absorption cross section ranges from 4.8 to 8.5×10-20 cm2, with bandwidths of 9.5—9.9 nm, whereas the maximum stimulated emission cross section varies in the range of 5.8—10.3×10-20 cm2. Continuous-wave laser operation has been realized at room temperature with the mixed crystals through longitudinal pumping with a diode laser. It was found that the laser oscillation behavior differs significantly from one mixed crystal to another:in the case of T=2% (T is the output coupling of the resonator), the coexistence and switching of σ, π polarization states occur on reducing the pump power in the laser oscillation of Yb0.005:Y0.298Gd0.697VO4 and Yb0.009:Y0.575Gd0.416VO4, while the laser oscillation of Yb0.007:Y0.407Gd0.586VO4 is capable of maintaining its π polarization state. In the case of T=5%, however, the laser oscillation generated with Yb0.009:Y0.575Gd0.416VO4 is purely σ-polarized, whereas the laser behavior of Yb0.005:Y0.298Gd0.697VO4 is similar to that exhibited in the case of T=2%.