Tm3+-doped fluorotellurite glass microsphere resonator laser at 23 μm

In this Letter, we report lasing at 2.3 µm in Tm3+-single-doped and Tm3+/Ho3+-codoped fluorotellurite glass microsphere resonators. By employing a 793 nm diode laser as a pump and exploiting whispering gallery mode microresonators (WGMRs), dual-wavelength lasing at 1.9 and 2.3 µm and triple-wavelength lasing at 1.9, 2.07, and 2.3 µm are achieved in Tm3+-doped and Tm3+/Ho3+-codoped microspheres, respectively. The introduction of Ho3+ ions significantly reduces the lasing threshold of Tm3+ at 2.3 µm because of energy transfer.