Tm:CALGO: Spectroscopy and Laser Operation at $\mathbf{2.32}\ \boldsymbol{\upmu}\mathbf{m}$

Calcium gadolinium aluminate (CaGdAlO 4 , shortly CALGO) is an attractive laser host material for doping with rare-earth ions. It belongs to the tetragonal class (sp. gr. I4/mmm) and exhibits a structure disorder (a random distribution of Ca ²⁺ and Gd ³⁺ cations over the same lattice sites). Still, CALGO features high thermal conductivity and appealing thermo-optical properties. The disordered nature of the host matrix determines a significant inhomogeneous spectral broadening for the dopant ions. Thulium (Tm ³⁺ ) doped CALGO was applied for femtosecond pulse generation at $2\ \upmu\mathrm{m}$ [1]. Recently, there is a great interest to another emission of Tm ³⁺ ions at $2.3-2.5\ \upmu\mathrm{m}$ according to the ³ H 4 → ³ H 5 transition, Fig. 1(a). The main constraint for ultrashort pulse generation from Tm-lasers at these wavelengths consists of the lack of broadband-emitting materials. In the present work, we explore the potential of Tm:CALGO for laser operation at $2.3\ \upmu\mathrm{m}$ , for the first time, to the best of our knowledge.