Lasing of Yb in a mixed YGdVO 4 crystal with bistability and polarization switching

Abstract

The orthovanadate crystals YVO4, GdVO4, and LuVO4 attract much attention as promising host materials for the trivalent Yb-ion since such crystals are characterized by large absorption and emission cross sections, broad absorption and emission bands, and higher thermal conductivities than most of the other Yb-doped materials. More interestingly, their laser operation is characterized by optical bistability, apparently a unique feature of Yb-doped vanadates, not found so far in other Yb-lasers or even in other solid-state lasers. The optically passive vanadates, YVO4, GdVO4, and LuVO4, as well as the stoichiometric YbVO4 exhibit the same zircon structure and continuous isostructural solid solutions can be expected. The absorption and emission spectra of Yb0.0054:Y0.3481Gd0.6465VO4, a specific compound in the mixed Ybt:YxGd1-x-tVO4 series, inherit the spectroscopic features of both Yb:YVO4 and Yb:GdVO4. We found that this Yb-doped solid solution also displays optical bistability in continuous-wave (cw) laser operation. The strongly pronounced bistability extends from Pabs=1.9 W to Pabs=3.4 W while the output power amounts to 0.98 W at the upthreshold. Distinct from the previously reported Yb:LuVO4 laser, coexistence and switching of the σ and π polarization states occur along with emission wavelength shift in the bistability region upon decreasing the pump power. Increasing the output coupling reduces the bistability region while expanding the coexistence region for the σ and π polarization states.