Yttrium lithium fluoride
Yttrium lithium fluoride (LiYF4, sometimes abbreviated YLF) is a birefringent crystal, typically doped with neodymium and used as a gain medium in solid-state lasers.
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Wikipedia
Yttrium lithium fluoride (LiYF4, sometimes abbreviated YLF) is a birefringent crystal, typically doped with neodymium and used as a gain medium in solid-state lasers.