Observation of Upconversion Lasing within a Thulium-Ion-Doped Glass Powder Film Containing Titanium Dioxide Particles

We demonstrated the upconversion lasing of a random medium composed of thulium-ion-doped fluorozirconate glass powders and submicrometer-sized titanium dioxide particles. Blue and red lasing emissions were induced by near-infrared excitation light via sequential multiphoton excitation, which enabled a highly efficient pumping of the gain particles within the random medium. The thresholds of the upconversion lasing were determined to be 2.6 and 6.3 kW/cm 2 in 800-nm and 450-nm wavelength regions, respectively.