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Mid-Infrared Laser Operation of Er:KY3F10 Crystal at 2.80 pm
Liza Basyrova*, Pavel Loiko, Jean-Louis Doualan, Abdelmjid Benayad, Alain Braud,
Christophe Labbé, and Patrice Camy
Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAPJMR 6252 CEA-CNRS-ENSICAEN, Université de Caen Normandie, 6 Boulevard Maréchal Juin, 14050 Caen CedeF4ance
*liza. basyrova@ensicaen.fr
The development of erbium (Er) lasers emitting in the mid-infrared, at ~2.8 ^m, is stimulated by theii wide range of applications in medicine, sensing, IR countermeasures and pumping of mid-infrared OPOs. Among the known gain media for mid-IR Er lasers, fluoride crystals such as LiYF4, BaY2Fg and CaF2 have attracted a lot of attention [1]. Potassium yttrium pentafluoride (KY3F10) is less studied member of the fluoride crystal family. However, when doped with rare-earth ions, it is known for broadband emission properties [2]. In the present work, we aimed to demonstrate first laser operation of a highly Er3+-doped KY3F10 crystal at ~2.8 ^m.
The crystal was grown by the Czochralski method using a composition of 22 mol% KF - 78 mol% (YF3 + ErF3). The nominal Er 3+ doping level was 15 at.% (with respect to Y 3+) and the actual ion concentration in the crystal Nei was 22.7^1020 cm-3 according to a segregation coefficient of ~0.98. Er:KY3F10 is cubic (sp. gr. O5h) and optically isotropic.
Figure 1(a) shows the stimulated-emission (SE) cross-sections, ose, for the 4In/2 " 4l13/2 Er3+ transition, calculated by the Fuchtbauer-Ladenburg equation using a radiative lifetime Trad of 6.14 ms and a luminescence branching ratio J of 15.8%. The maximum ose value is 1.77^10-20 cm2 at 2730 nm, corresponding to the zero-phonon line transition.
The quasi continuous-wave (qCW) laser operation of a 2.2-mm-thick sample was achieved under Ti:Sapphire laser pumping at two wavelengths, Ap = 970.6 nm and 801.3 nm (pumping into the 4In/2 and 4I9/2 states, respectively). A hemispherical cavity formed by a concave output coupler ( transmission: Toc = 1.5%, radius of curvature: -75 mm) and a plane pump mirror was used. The pump was focused into the laser element using a 75 mm AR-coated achromatic lens. Under pumping into the 4Ih/2 state (the upper laser level) , the Er:KY3F10 laser generated a maximum output peak power of 255 mW at 2800 nm with a slope efficiency n of 10.9% (versus the absorbed pump power) and a low laser threshold Pth of 58 mW (these results correspond to a duty cycle of 1:4), Fig. 1(b). When using
the 4I15/2 " 4I9/2 pump transition, the output power was limited to 58 mW at the same wavelength with reduced n = 18.9% and slightly higher Pth of 71 mW. The spectra of unpolarized l aser emission are shown in Fig. 1(c).
Er:KY3F10 crystals with optimized doping levels (between 5 - 15 at.%) are promising for mode -locked lasers at ~2.8 ^m.
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Wavelength (|im) Absorbed (peak) pump power (W) Wavelength (nm)
Fig. 1. 15 at.% Er:KY3Fio laser crystal: (a) stimulated-emission (SE) cross-sections, ose, for the 4In/2 ^ 4Ii3/2 Er3+ transition; (b,c) laser performance under Ti:Sapphire pumping: (b) input-output power dependences, n - slope efficiency; (c) typical spectra of output emission, inset - laser mode profile in the far-field.
[1] C. Labbe, J. L. Doualan, P. Camy, R. Moncorgé, M. Thuau, The 2.8 ^m laser properties of Er3+ doped CaF2 crystals, Opt. Commun., vol. 209, pp. 193-199 (2002).
[2] L. Guillemot, P. Loiko, R. Soulard, A. Braud, J. L. Doualan, A. Hideur, P. Camy, Close look on cubic Tm:KY 3F10 crystal for highly efficient lasing on the 3H4 ^ 3H5 transition, Opt. Express, vol. 28, pp. 3451-3463 (2020).
