Tm³⁺-doped fluorotellurite glass microsphere resonator laser at 2.3  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.