Growth and spectroscopic properties of a novel Tm:CaGdAl3O7 crystal for ∼2 μm laser

The growth and spectroscopic properties of a novel Tm:CaGdAl3O7 crystal were studied for the first time. The XRPD pattern shows that the crystal belongs to the tetragonal system with the cell parameters of a = b = 7.7125 Å and c = 5.0683 Å. The absorption and fluorescence spectra were recorded and the spectroscopic performance was systematically analyzed with the Judd–Ofelt theory. The absorption cross-section was calculated to be 0.542 × 10−20 cm−2 at 788.5 nm with a full width at half maximum (FWHM) of 36 nm. The FWHM of fluorescence spectrum was up to 228 nm, and the determined emission cross-sections were 0.439 × 10−20 cm2 at 1817 nm and 0.388 × 10−20 cm2 at 1940 nm, respectively. The fluorescence lifetime of 3F4 energy level in Tm:CaGdAl3O7 crystal was found as 4.42 ms. The gain cross-section at the wavelength over 1800 nm becomes positive when the population inversion level reaches 20%. The experimental results show that Tm:CaGdAl3O7 is a promising crystal that can be used in ∼2 μm tunable and ultrashort pulse lasers.