A transmitting optical element of polycrystalline material that includes crystallites of magnesium spinel MgAl2O4 or lutetium-aluminum garnet Lu3Al5O12, wherein the polycrystalline material includes an average total concentration of foreign element contamination caused by Y, Sc, Co, Ni, Zr, Mo, Sn and/or Nb of less than 50 ppm, preferably of less than 20 ppm, and more preferably of less than 15 ppm.