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

[1] Yttrium is the substitutional element in LiYF4.

The hardness of YLF is significantly lower than other commons crystalline laser media, i.e. yttrium aluminium garnet.

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