2 μm laser oscillation of Ho^3+:Tm^3+-codoped silica microspheres

Abstract

2 μm laser oscillation with a low threshold has been achieved in Ho³⁺:Tm³⁺-codoped silica microspheres (HTCSMs). Ho³⁺:Tm³⁺-codoped solgel functionalization film is applied to the surface of a silica microsphere, and an optical tapered fiber is adopted to couple an 808 nm continuous-wave laser to serve as the pump light source. Multimode and single-mode laser oscillations around 2 μm within the eye-safe wave band are observed due to the I₇5→I₈5 transitions of Ho³⁺ ions sensitized by Tm³⁺. The morphology characteristics of microspheres determine the multimode laser oscillation spectrum. The free spectral range is in good accordance with the calculated value based on Mie scattering theory. The HTCSM laser oscillation shows characteristics of good capability, simple process, high flexibility, and low cost.