Wednesday, 25 May 2005 - 1:30 PM

This presentation is part of: Applications of Vibrational Spectroscopy in Forensic Science II

Novel Method for ATR Microanalysis of Multilayer Paint Chips

Thomas J. Tague Jr., Bruker Optics, Billerica, MA

A new reflecting objective for attenuated total reflection (ATR) infrared microanalysis has been designed to provide excellent sample viewing, high infrared sensitivity, and increased ease-of-use. The ATR objective incorporates a unique vertical sliding mechanism, which allows the internal reflection element (IRE) to be positioned out of the field of view (FOV) for viewing of the sample and in the FOV for high throughput infrared analysis. When the IRE is out of the FOV, contrast enhancement methods can be readily employed, such as visible polarization, fluorescence illumination, darkfield illumination, etc. The IRE is an anvil design with an 80-micron tip providing access to small areas within the sample of interest.

There are five contact pressure levels to choose from, where the contact pressure can be optimized for the sample hardness and tractability. Optimal pressure is indicated by an LED indicator and an audible beep. The germanium IRE functions as an immersion lens yielding a 4x magnification of the IR field aperture. This increases the spatial resolution to significantly better than the wavelength of light.

Multilayer paint chips from ancient works of art, aircraft, and automobiles, were visualized utilizing crossed polarized light and fluorescence illumination. The IR aperture was visually adjusted to mask each area of interest followed by infrared ATR data collection. Pure spectra were obtained for each component of the chip without contamination from adjacent areas.

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