Red Ridge Pr:LiYF₄ Waveguide Laser with >50% Optical Efficiency

Praseodymium (Pr<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>+) doped lithium fluoride crystal (LiYF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>) has recently emerged as a prominent laser material for the development of efficient, multi-color coherent light sources directly emitting visible light under pumping in the blue [1]. The waveguide configuration offers compact (monolithic) design, low laser thresholds, good overlap of the pump and laser modes, and better thermal management as compared to optical fibers. Liquid Phase Epitaxy (LPE) is a viable solution for the growth of low-loss (< 0.1 dB/cm), single-crystalline waveguiding layers supporting Watt-level output powers. Recently, microstructuring of such epilayers by precision diamond saw dicing was proposed as an efficient approach for fabricating surface channel (ridge) waveguides with small surface roughness and well-defined cross-sections [2]. In this work, we report on the first ridge Pr:LiYF4 waveguide laser featuring >50% optical efficiency.