Effects Of Contamination On Performance Of Optical Coatings For Space Applications

Space is an extremely complicated and harsh environment, the stability of the optical system’s performance and lifetime will be face with various challenges when operated in space environment. The hazards include high vacuum, solar UV radiation, charging particles radiation, atomic oxygen, severe temperature cycles, contamination, micrometeoroids and debris. Optics will always be plated with optical films to improve its performance. As the weakest link in optical system, optical films of course are the important factor which will restrict the optical system’s performance and lifetime. In this paper, we analyzed the constituents of risks in space environment, and combined laboratory apparatus to design a proper accelerated experiment. The effects of space charging particle and solar UV irradiation on the performance of optical films under the condition of contamination are investigated respectively.We prepared Al+Mg F2 high reflectance film by Vacuum resistive heating evaporation and prepared Hf O2/Si O2 structure anti-reflective film at 1064 nm by Ion beam sputtering deposition respectively. The charging particles irradiation experiment was carried on by radiation apparatus of; irradiated samples are treated with solvent cleaning, UV cleaning and high annealing, the performance degradation of samples after charging particles irradiation in different spectrum range are compared; We try to illustrate the mechanism of performance degradation and radiation damage in different spectrum range under the condition of contamination. The results indicate that charging particles radiation and radiation-induced contamination are the reason of optical performance degradation of the samples. Especially the Al+Mg F2 film sample in UV range degraded more seriously. Using component solvent of alcohol and ethereal can basically cleaned the surface contamination of the samples. After cleaning, the main reason of optical performance degradation of the samples is radiation damage. The radiation damage of Al+Mg F2 film sample in the UV range is more serious than the Hf O2/Si O2 structure anti-reflective film sample in the infrared range. After irradiation, the surface defects of the Al+Mg F2 film sample obviously increased. The radiation damage of the Hf O2/Si O2 structure anti-reflective film sample is mainly caused by displacement effect that lead to vacancy damage.Hf O2 and Si O2 are usually used to prepare laser optical film at 1064 nm as the low and high refractive index material due to their excellent physical and chemical properties and higher laser induced damage threshold. We prepared Hf O2/Si O2 structure anti-reflective film at 1064 nm by Ion beam sputtering deposition. The contamination was made by spin coating using 2ml of dioctylphthalate(DOP). Solar UV radiation and radiation-induced contamination experiment are performed by laboratory UV radiation apparatus. After the radiation, spectrophotometer and laser calorimeter are used to measure the change of the optical parameters of the sample; Atomic force microscope is used to measure surface roughness; Optical microscope is used to observe the surface contamination and its evolution; These experimental data of the optical performance degradation and the behavior of the Hf O2/Si O2 structure anti-reflective film sample under the UV radiation and radiation-induced contamination are useful to space application of optical coatings.