Resonantly Pumped Tm-Doped and Y/Lu/Gd/La Buffered CaF₂ Lasers Tunable in Wide Wavelength Range of 1820–2062 nm

Thulium lasers operating on the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{3} \mathrm{F}_{4} \rightarrow{ }^{3} \mathrm{H}_{6}$</tex> transition are efficient sources of radiation near 2 μm. By selecting a suitable host material, these lasers can be tuned over relatively broad wavelength ranges. Tunable thulium lasers have potential applications in atmospheric sensing, medical procedures, or as pump sources for optical parametric oscillators generating in the mid-infrared region. Among suitable laser materials for these applications, CaF2 stands out due to its excellent thermal and optical properties and broad spectral lines enabling tuning in a wide spectral range. This exceptional behavior is due to a strong rare-earth ions clustering causing inhomogeneous spectral line broadening [1]. Furthermore, incorporating optically inactive “buffer”, such as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{Y}^{3+}$</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{La}^{3+}$</tex>, has been shown to enhance the spectroscopic and laser properties of the active media by modifying the cluster composition and, consequently, the local multi-ligands around the active ions [2], [3]. In this paper, we focus on the wavelength tuning of 2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> lasers employing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{CaF}_{2}$</tex> crystals codoped with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Tm}^{3+}$</tex> ions and various “buffer” ones.