Effects of ultraviolet solar photons on thin-film optical filters for space applications

Ultraviolet solar photons could induce some variation in the performance of optical coatings exposed to solar irradiation. Consequently optical components and instruments containing such coatings can suffer performance degradation in the space environment. The effects of ultraviolet solar photons on the transmittance of single layer coatings and optical filters, has been investigated. The beamline of a synchrotron light source was used for the irradiation test, being the irradiance in the ultraviolet region comparable to the solar spectrum. Some changes induced by such irradiation are detected in silicon dioxide, which shows an increased absorption below 350 nm. On the contrary, hafnium oxide characteristics seem unaffected. Narrow-band filters containing both these materials show a reduction of transmission in the passband.