Impact of temperature on optical properties of Tm³⁺-doped disordered oxide crystals for cryogenic lasers emitting near 1.9 μm: a comparative study

Optical spectra of transitions between the ³H₆ and ³F₄ manifolds of Tm³⁺ ions in disordered crystal lattices of Gd₃Ga₅O₁₂–Gd₃Al₅O₁₂, Lu₂SiO₅–Gd₂SiO₅ solid solutions and in LiNbO₃ crystals were recorded at several temperatures between 80 K and 300 K. Obtained experimental data were analyzed to examine the spectroscopic peculiarities of Tm³⁺ transitions that governs the temperature dependence of absorption and emission properties. The impact of structural disorder on the lasing ability at cryogenic temperatures upon resonant (in-band) optical pumping was assessed. In particular, it was found that peak stimulated emission cross section values at respective free generation wavelengths increase by a factor of two when samples examined are cooled down from 300 K to 80 K. At 80 K the laser operation wavelength can be tuned in regions 1940–2063 nm for GAGG: Tm³⁺, 1764–1853 nm for LNO: Tm³⁺ and 1778–2074 nm for LGSO: Tm³⁺.