Effect of Tm³⁺ concentration on the emission wavelength shift in Tm³⁺-doped silica microsphere lasers

In this work, a Tm³-doped solgel silica microsphere lasing at 2.0 μm is reported. Microspheres with different Tm³ concentrations are fabricated by overlaying different Tm³ concentration solgel solutions on the surface of a pure silica microsphere resonator and then annealing the sample with a CO₂ laser. Based on a traditional fiber taper–microsphere coupling method, single and multimode microsphere lasing in the wavelength range 1.8–2.0 μm is observed if an 808 nm laser diode is used as a pump source. A relatively low threshold pumping power of 1.2 mW is achieved using this arrangement. This solgel method allows for an easy varying of the Tm³ doping concentration. The observed laser output shifts to longer wavelengths when the Tm³ doping concentration increases. This has been explained by the larger Tm absorption at shorter wavelengths. The ability to fabricate solgel co-doped silica glass microlasers represents a new generation of low threshold and compact infrared laser sources for use as miniaturized photonic components for a wide range of applications, including gas sensing and medical surgery.