Effect of a silicone contaminant film on the transmittance properties of AR-coated fused silica

摘要

We present the results of a laboratory test to determine the effects of bulk-deposited DC-704 silicone-oil contaminant film on the transmittance properties of an anti-reflective (AR) coated fused-silica optical substrate. Testing and optical measurements were performed in vacuum in the Boeing Contamination Effects Test Facility (CETF). The test and measurement procedures are described herein. Measurement results are presented showing the change in transmittance characteristics as a function of contaminant deposit thickness and vacuum-ultraviolet (VUV) exposure levels. The results show an initial degradation in the transmittance of the contaminated sample. This is followed by a partial recovery in transmittance as the sample is exposed to additional VUV radiation. The results also show a loss of transmittance in the ultraviolet portion of the spectrum and an increase in transmittance in the infrared portion of the spectrum. Thin-film interference analysis indicates that some of the observed transmittance results can be successfully modeled, but only if the contaminant film is assumed to have the complex index of refraction of SiO_2 rather than DC-704 silicone oil. Post-test Scanning Electron Microscope (SEM) scans of the test sample indicate the formation of contaminant islands and the presence of a thin uniform contaminant film on the sample.