Calcium Fluoride (CaF2) was identified among the first host crystals for active laser media. However, due to the need of charge compensation of Nd3+-doped fluorite crystal structures, other host materials like YAG, oxide and fluorite glasses were preferred over the years. Recent developments made on ytterbium-doped alkaline-earth fluorides have shown that it is possible to have better scalability of crystal growth, very high thermal conductivity, high laser-induced damage threshold, longer emission lifetime, lower nonlinear refractive index and large emission wavelength tuning range. Due to these reasons, Yb-doped CaF2 has once again proved to be a competitive material for high-energy and high-power operations.
Waveguides confine light propagation resulting in reduced lasing thresholds and enhanced laser efficiencies. By properly managing the three-dimensional translation of the focal volume of pulsed lasers, it is possible to create waveguides and other 3D structures inside crystals. Recently, depressed cladding waveguides written inside CaF2 were reported. In this work, we will present the first, to the best of our knowledge, double track waveguides inscribed inside doped and undoped CaF2 crystal with different pulse energies. Waveguide characterization, determination of mode-field diameter, analysis of polarization dependent guiding and also direct refractive index change measurements of the waveguides were performed and will be presented. Additionally, single pass gain and lasing experiments will be demonstrated both theoretically and experimentally.