Abstract: The objectives of the present invention are to prevent or inhibit the deterioration of optical systems that determine the longevity of an optical apparatus which delivers effects such as light transmission, diffraction, reflection, spectrum generation, and interference, and these combinations, and by so doing, decrease the frequency of maintenance operations such as window replacement and to reduce the costs for such operations. This invention is characterized by steps of creating a near vacuum zone with a presence of active energy to excite an oxidation reaction of carbon wherein the near vacuum zone faces the lighting surfaces of the optical system; generating negative ions or radicals in the near vacuum zone such as unstable chemical seeds containing oxygen atoms, such as OH radicals, OH— ions, ozone, O2— ions, O-radicals; and removing or reducing the accumulated carbon which deposits on the lighting surface, by reacting the deposited carbon with the negative ions or radicals.