Meller Optics Inc. offers sapphire wave plates from 0.3 to 4.7 µm for Er:YAG and holmium lasers at 2.94 and 2.10 µm, respectively. They are available in a quarter-wave version for switching polarization between linear and circular or vice versa, and in a half-wave version for changing the state of polarization completely. The devices feature 10-5 scratch-dig surface quality and less than 1 arc sec parallelism. The company says the wave plates provide superior damage resistance to quartz and mica and are impervious to chemicals. The optics are offered with diameters ranging from 10 to 30 mm with either a V coat or a broadband AR coating at ≤0.25% reflectance per surface.