Ho-Yb Fluoride Glass Fiber for Green Lasers

Upconversion emissions of Ho3+ ion sensitized by Yb3+ ion in fluoride glasses with different phonon frequencies were investigated. The green emission of 543nm is stronger in a fluorozircoaluminate glass (AZF) than in a fluorozirconate glass (ZBLAN). It suggests that the emission is primarily governed by the Yb3+-Ho3+ energy transfer rate rather than by the multiphonon decay rate of the emitting level. The concentrations of Ho3+ and Yb3+ were determined to provide higher emission efficiencies. Using fibers made of a AZF glass optimized in the dopant concentrations, gains were measured at 543nm with Тi:Аl2O3 laser pumping at 974nm. A maximum gain obtained for a 2mm fiber was 0.5dB for 90mW incident power. By tuning a pump wavelength, strong blue upconversion emissions were firstly, to our knowledge, observed in the Ho3+-Yb3+ system.