Far-IR optical properties of Y_3Al_5O_12, LiYF_4, Cs_2NaDyCl_6, and Rb_2NaYF_6

The refractive indices n, power absorption constant α (cm^−1), and percent transmission T of YAG and YLF were measured in the 10–100-cm^−1 range. Only the percent transmission T of thin samples of the elpasolite hexachloride Cs_2NaDyCl_6 and hexafluoride Rb_2NaYF_6 was measured in the 10–400-cm^−1 range since T was 2–3%. A brief discussion of the far-infrared (FIR) laser possibilities of rare-earth doped crystals is presented.