Solid-State Lasers With Direct Emission at 413 nm and 435 nm

Many fields in industry and research rely on lasers in the violet and blue spectral range. However, most of them are bulky and complex owing to multiple steps of frequency conversion. Reports on simple direct emitting solid-state lasers in the UV and blue spectral range are sparse, and output powers are limited to a few mW. Here, we present new solid-state lasers directly emitting around 413 nm and 435 nm based on Tb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>:LiYF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> (Tb:YLF) as the gain medium. Tb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> has gained attention in recent years as a laser ion for yellow laser emission from the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^5 \mathrm{D}_4$</tex> level under blue [1] or UV pumping [2]. The latter approach works efficiently at typical Tb doping concentrations of 15% or higher [3] due to a cross-relaxation process (see Fig. 1(a)). Suppressing this cross relaxation by reduced doping concentrations of below 1% gives rise to a fluorescence lifetime longer than 2 ms of the violet-blue emitting <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^5 \mathrm{D}_3$</tex> level. Under UV excitation this results in fluorescence ranging from 375 nm to 485 nm, with the strongest emission peaks at 415 nm and 435 nm terminating in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^7 \mathrm{F}_5$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^7 \mathrm{F}_4$</tex> levels, respectively.