Absorption coefficients and scattering losses of TGG, TGP, KTF, FS, and CeF₃ magneto-optic crystals in the visible via cavity ring down spectroscopy

We demonstrate a method for determining small absorption coefficients and surface scattering losses of crystals using cavity ring down spectroscopy, and perform measurements on crystals of TGG, TGP, FS, KTF, and CeF₃, at 532nm and 634nm. We separate the surface-scattering and absorption losses by using crystals of different length. The measurements differ from those in the literature, especially for small absorption coefficients. We define a figure of merit (FoM) for magneto-optic crystals in signal-reversing cavity-ringdown polarimetry, which depends on the cavity losses, and on the crystal Verdet constant and absorption coefficient, and use it to evaluate the crystals for suitability for intra-cavity applications. We show that TGP has a significantly higher FoM compared to the other crystals, for crystal lengths up to 16 mm, whereas CeF₃ and FS outperform TGP for longer crystals.