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4 September 2018 Intense photoluminescence and optical gain in rare-earth doped Polycrystalline Sapphire: a new bulk media for high-power phosphors and high-energy lasers
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Abstract
Conventional materials engineering approaches for polycrystalline ceramic gain media rely on optically isotropic crystals with high equilibrium solubility of luminescent rare-earth (RE) ions. Crystallographic optical symmetry is traditionally relied upon to avoid scattering losses caused by refractive index mismatch at grain boundaries in randomly oriented anisotropic crystals and high-equilibrium RE-solubility is needed to produce sufficient photoluminescence (PL) for amplification and oscillation. These requirements exclude materials such as polycrystalline sapphire/alumina that have significantly superior thermo-mechanical properties (Rs~19,500Wm-1), because it possesses 1) uxiaxial optical properties that at large grain sizes, result in significant grain boundary scattering, and 2) a very low (~10-3%) RE equilibrium solubility that prohibits suitable PL. I present new materials engineering approaches operating far from thermodynamic equilibrium to produce a bulk Nd:Al2O3 medium with optical gain suitable for amplification/lasing. The key insight relies on tailoring the crystallite size to the other important length scales-wavelength of light and interatomic dopant distances and show that fine crystallite sizes result in sufficiently low optical losses and over-equilibrium levels of optically active RE-ions, the combination of which results in gain. The emission bandwidth is broad, ~13THz, a new record for Nd3+ transitions, enabling tuning from ~1050nm-1100nm and/or ultra-short pulses in a host with superior thermal-mechanical figure of merit. Laser grade Nd:Al2O3 opens a pathway for lasers with revolutionary performance.
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
E. H. Penilla, L. F. Devia-Cruz, M. A. Duarte, C. L. Hardin, Y. Kodera, and J. E. Garay "Intense photoluminescence and optical gain in rare-earth doped Polycrystalline Sapphire: a new bulk media for high-power phosphors and high-energy lasers", Proc. SPIE 10755, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications XII, 1075509 (4 September 2018); https://doi.org/10.1117/12.2322108
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