CeF ₃ single crystals for UV‐VIS‐IR optical isolators

Optical isolators (OIs) are needed to protect laser sources from back‐reflections. Driven by the fast‐growing market of laser marking and machinery, and the increasing cost of rare‐earth‐based permanent magnets, single‐crystalline Faraday rotators (FRs) with a large Verdet constant V are highly desired to reduce the cost and size of OIs. Furthermore, the need for finer laser procedures (marking, cutting, welding) is shifting the used laser emissions toward shorter wavelengths: into the visible (VIS), where standard Tb 3 Ga 5 O 12 (TGG) has a poor transmittance, and even into the ultraviolet (UV), where TGG possesses overlapping Tb 4f‐4f absorption bands. In recent years CeF 3 has emerged as a new FR with a unique transmittance and an outstanding V in the UV wavelength region, and a superior figure‐of‐merit in the VIS range compared to TGG. Recently, its small thermal lensing and high damage threshold for high‐power have been demonstrated, exhibiting optical isolation > 30 dB under 600 W @ 1070 nm. This review first summarizes the basic properties and crystal growth of CeF 3 , then focuses on its Faraday magneto‐optical performance. Last but not the least, the typical crystal defects encountered during the development of CeF 3 are discussed.