Bulk and surface-scattering loss measurements of CeF3 crystals at 532 nm via cavity ring down spectroscopy

CeF 3 is a relatively new magneto-optical crystal with a wide transparency window (down to 300 nm) and an outstanding Verdet constant in the UV and visible spectral regions. The high transmittance of this fluoride in the visible was recently demonstrated in cavity ring-down measurements at 532 nm, where bulk losses of no more than 0.004 cm − 1 were measured (Xygkis et al., 2023), although the total losses were significantly higher and dominated by surface scattering. Here, we show that by reducing surface scattering and improving crystal quality, by suppressing the random formation of hexagonal micro-void defects in the bulk of the crystal, which cause bulk scattering, lead to significantly reduced overall losses. Bulk loss coefficients as low as 0.002 cm − 1 at 532 nm, half the previously measured value, are achieved in select samples, which is the current state-of-the-art in high-quality CeF 3 single crystals. Further elimination of micro-voids in the bulk is expected to further improve transmittance. Compared to other magneto-optical crystals and glasses, the present CeF 3 crystals achieve the highest values of the Figure of Merit (FoM) we have defined for both single-pass and multi-pass (optical cavity) applications. • Growth of high quality CeF 3 crystals for very low bulk and surface scattering losses. • Measurement of very low bulk scattering losses of CeF 3 crystals (<0.002 cm −1 ), using cavity ringdown spectroscopy. • Demonstrate that these CeF 3 crystals have the highest magneto-optic Figure of Merit for single-pass or multi-pass applications, in the near UV and visible.