Deep-red planar waveguide laser operation of Eu³⁺:KY(WO₄)₂ layers

We report on the first deep-red europium planar waveguide laser. It employs 30-µm thick heavily-doped 11.5 at.% Eu:KY(WO₄)₂ layers grown by liquid phase epitaxy on undoped substrates using K₂W₂O₇ as a solvent. When pumped with a green laser at 532 nm, the Eu-waveguide laser delivers a maximum output power of 7 mW at 704.7 nm with a slope efficiency of 9.5%, a laser threshold of 21 mW, and linear polarization. The waveguide propagation losses are as low as 0.05 dB/cm. The morphology, vibronic, and spectroscopic properties of the epitaxial layers are also studied. In the deep red, for the ⁵D₀ → ⁷F₄ transition, the stimulated-emission cross-section reaches 1.76 × 10^-20 cm² at 704.7 nm for light polarization E || N _p, and the luminescence lifetime of the ⁵D₀ manifold is 472 µs.