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Wednesday, May 15 • 2:30pm - 3:00pm
(Research & Technical Studies) Hyperspectral Imaging on the Microscopic Scale: Challenges and Successes of Instrument Design for Materials Characterization

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Hyperspectral imaging has become an increasingly ubiquitous tool for the technical study of cultural heritage objects. It has been used to non-invasively characterize pigments and binding media on painted surfaces, as well as a variety of other object types from manuscripts to wood, over a wide field of view. However, the interpretation of hyperspectral data cubes can be complicated by the nonlinear mixing response of two or more colorants present below the resolution limits of the camera. Consequently, complimentary point analysis techniques, such as Raman or FTIR spectroscopy, are usually employed to obtain ground truth detailed material information. When possible, samples are removed and mounted in resin for further elemental and molecular characterization. However, some challenges are encountered with traditional analytical techniques when used to map molecular phases in these samples, notably the contaminating fluorescence background which can swamp the signal in Raman microspectrometry or the low signal-to-noise ratio in FTIR which can necessitate long integration times prohibitive for imaging. Avoiding these obstacles, a hyperspectral imaging technique with high spatial resolution would offer advantages for characterizing at the sub-micron range, with little additional sample prep or need to access more expensive equipment such as electron microscopy. As of yet, hyperspectral microscope configurations are rarely applied outside of the biological sciences. However, a recent hyperspectral optical microscopy experiment demonstrated excellent spatial resolution for the detection of single silver nanoparticles down to 100 nm diameters using a high numerical aperture objective, indicating the technique’s potential for material studies across many disciplines. This work presents the design and development of a simple dark field, reflectance hyperspectral microscope system for the purpose of extracting high spatially- and spectrally-resolved information, particularly for pigmented samples. Using a tunable light source to illuminate monochromatically over a range of visible to Near Infrared wavelengths, diffusely reflected light was collected with a long working distance, 20x objective. The challenges of fully automating and mechanizing the experimental construction of the hyperspectral data cube will be discussed as well as best practices determined for normalizing the acquired reflectance spectra as the surface texture of reflectance standards can become problematic under magnification. The developed microscope was used to characterize the pigment distribution in the stratigraphy of painting cross sections as well as other materials systems such as red opaque glass.

Speakers
avatar for Lindsay Oakley

Lindsay Oakley

Postdoctoral Fellow, Center for Scientific Studies in the Arts
Lindsay completed her PhD in Materials Science and Engineering at Northwestern University in 2017 and spent time as a postdoc at the Natural History Museum of Denmark. At the Center for Scientific Studies in the Arts, her research interests include using combinations of experimental... Read More →

Co-Author
avatar for Marc Sebastian Walton

Marc Sebastian Walton

Co-Director, Research Professor, Center for Scientific Studies in the Arts
Marc Walton joined the Northwestern University / Art Institute of Chicago Center for Scientific Studies in the Arts in 2013 as its inaugural Senior Scientist and as a Research Professor of Materials Science and Engineering at Northwestern University. In January of 2018, he was appointed... Read More →
avatar for Victoria Cooley

Victoria Cooley

Graduate Student, Northwestern University
Victoria is a PhD student in Materials Science & Engineering at Northwestern University. Her research interests include combining microscopic hyperspectral measurements with super-resolution imaging techniques for materials characterization. She received her BS in Chemistry with a... Read More →


Wednesday May 15, 2019 2:30pm - 3:00pm EDT
Nehantic/Pequot/Paugussett Rooms Sky Convention Center, Mohegan Sun
  Specialty Session, Research & Technical Studies