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Molecular surface contaminants can cause degradation of optical systems, especially if the contaminants exhibit strong absorption bands in the region of interest. Different strategies for estimation of spectral degradation responses due to uniform films for various types of systems are reviewed. One tool for calculating the effects of contaminant film thickness on signal degradation in the mid IR region is the simulation program CALCRT. The CALCRT database will be reviewed to correlate spectral n and k values associated with specific classes of organic functional groups. Various schemes are also investigated to estimate the spectral degradation in the UV-Vis region. Experimental measurements of reflectance changes in the IR to UV-Vis regions due to specific contaminants will be compared. Approaches for estimating changes in thermal emissivity and solar absorptivity will also be discussed.

Semi-volatile residues on aerospace hardware can be analyzed using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). This method can be correlated with quantitative Mil-STD 1246 NVR measurements while simultaneously providing qualitative identification of a large variety of compounds. Its high sensitivity supports the direct sampling of small areas of critical surfaces. This method involves transferring the contaminant film to a small solvent-saturated wipe, followed by extraction of the wipe, then concentration of the solvent extract and subsequent spectroscopic analysis using an FT-IR with a diffuse reflectance accessory. A library of standard curves for different classes of typical aerospace contaminants has been established. Quantitative analysis has been proven successful over orders of magnitude and detection limits exceeding 0.1 ug/cm 2 are routinely achieved. Several practical applications have been performed using this analytical method and detailed discussion of analysis techniques is presented. The discussion will include: instrumentation setup, selection and preparation of sample collection materials, sample extract preparation, preparation of standard calibration curves and spectral interpretation.

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