Femtosecond-Laser-Written Depressed-Cladding Waveguide Laser in Tm³⁺:CaF2

Femtosecond Direct Laser Writing (fs-DLW) is a powerful technique of fabricating 3D photonic microstructures in transparent dielectric materials doped with rare-earth ions for waveguide (WG) laser applications [1]. It benefits from high precision of inscriptions, short fabrication times, and a variety of available WG geometries. Laser waveguides based on thulium ions (Tm ³⁺ ) with emission around $2\ \mu \mathrm{m}$ (the ³ F 4 → ³ H 6 transition) are appealing as seed sources for WG and fiber amplifiers for medical and sensing applications. Calcium fluoride (CaF 2 ) is an attractive host matrix for rare-earth doping because of its high thermal conductivity and strong ion clustering leading to broadband (“glassy-like”) emission properties. In the present work, we report on the first Tm ³⁺ :CaF 2 waveguide laser.