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24LS-O-1
Crystalline and electronic structure, spectroscopy and laser operation of Tm:KY(MoO4)2 crystal
Sami Slimi1*, Pavel Loiko2, Anna Volokitina13, Anatoly Pavlyuk4, Rosa Maria Solé1, Josep Maria Serres1, Uwe Griebner5, Valentin Petrov5, Magdalena Aguiló1, Francesc
Díaz1, and Xavier Mateos1#
1-Universitat Rovira i Virgili, Física i Cristalografía de Materials i Nanomaterials, FiCMA-FiCNA, Marcellí Domingo 1, 43007 Tarragona, Spain, #Serra Húnter Fellow 2-Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), UMR 6252 CEA-CNRS-ENSICAEN, Université de Caen, 6 Boulevard du Maréchal Juin, 14050 Caen Cedex 4, France 3-ITMO University, 49 Kronverkskiy Pr., 197101 St. Petersburg, Russia 4-A. V. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3
Lavrentyev Ave., 630090 Novosibirsk, Russia
5-Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Str. 2a, 12489 Berlin,
Germany
*samislimi07@gmail.com
Among the laser host crystals for thulium (Tm3+) ions, double tungstates and molybdates with chemical formula ARE(XO4)2 (RE = Y, Gd, Lu and X = W, Mo) occupy a special position. They provide intense and broad spectral bands for dopant ions, high doping levels, weak concentration quenching and suitable thermo-optic properties. Efficient Tm lasers based on monoclinic potassium rare-earth double tungstates are known [1] but their double molybdate counterparts, e.g., KY(MoO4)2, are poorly studied. They feature a layered structure that enhances the polarization anisotropy of the spectroscopic properties and leads to a perfect natural cleavage which is attractive for microchip lasers. In the present work, we report on the structure refinement, spectroscopy and laser operation of Tm:KY(MoO4)2.
A single-crystal of 3 at.% Tm:KY(MoO4)2 was grown by the Low Temperature Gradient (LTG) Czochralski method [2]. Its crystal structure (orthorhombic, sp. gr. D142h - Pbna) was refined by the Rietveld method, Fig. 1(a). The anions [Y(MoO4)2]- form porous layers parallel to the b-c plane. The linkage of these layers along the a-axis is weak, which determines the perfect cleavage along the (100) plane, Fig. 1(b). The electronic structure of KY(MoO4)2 was calculated using the density functional theory (DFT). This crystal is an indirect band-gap material (the calculated bandgap is 3.47 eV). The theoretically obtained refractive index of KY(MoO4)2 is <n> = 2.09 at ~2 ^m.
The polarized absorption and luminescence of Tm3+ ions were measured. The maximum SE cross-section for the 3F4 ^ 3H6 transition ose = 2.70*10"20 cm2 at 1856 nm (for E || b) and its emission band is smooth and broad extending above 2 ^m. The reabsorption-free lifetime of the 3F4 state is 1.63 ms. The crystal-field splitting of the Tm3+ multiplets was determined, e.g. AE = 492 cm-1 for the ground state.
Continuous-wave diode-pumped lasing was achieved in a mechanically cleaved thin (70 ^m) film yielding a maximum output power of 131 mW at 1972 nm with a slope efficiency of 45.2% and linearly polarized output (E || b). Fig. 1(c). Tm:KY(Mo04)2 is promising for microchip lasers.
Fig. 1. Tm:KY(MoO4)2 crystal: (a) X-ray powder diffraction (XRD) pattern showing the result of the Rietveld refinement; (b) Projection of the crystal structure parallel to the b-a plane; (c) diode-pumped laser performance of (100)-oriented cleaved thin-film, q - slope efficiency.
[1] J. M. Serres, X. Mateos, P. Loiko, K. Yumashev, N. Kuleshov, V. Petrov, U. Griebner, M. Aguiló, F. Díaz, Diode-pumped microchip Tm:KLu(WO4)2 laser with more than 3 W of output power, Opt. Lett., vol. 39, pp. 4247-4250 (2014).
