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14 May 2018 Infrared spectroscopy below the diffraction limit using an optical probe
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Optical (visible) microscopy has established itself as an invaluable tool in Materials Science, and perhaps the canonical technique in Biology. Unfortunately, an optical image provides extremely limited information regarding chemical composition. A great deal of effort has been spent to circumvent this limitation through the use chemical dyes - most notably fluorescent markers - to achieve contrast between different chemical species. Infrared spectroscopy is an ideal technique to chemically fingerprint materials. Specifically, infrared microspectroscopy holds great promise as a labelless technique to achieve chemically specific microscopy. Unfortunately, the long wavelengths of the infrared lead to low spatial resolution in infrared microscopy, on the order of several microns. Traditionally, this limitation has been circumvented via scanning probe techniques such as s-SNOM and AFM-IR. While the scanning probe techniques provide excellent resolution, their contact nature and low signal levels limit the speed at which images can be acquired. We have developed a new technique to collect infrared hyperspectral images below the IR diffraction limit. Optically Sensed photothermal InfraRed Imaging micro-Spectroscopy (OSIRIS) permits the construction of infrared images on a resolution limited by the wavelength of the probe beam. In this technique, an infrared laser is used to excite the sample, while a short wavelength probe beam senses the resultant change in temperature. With this technique, hyperspectral images can be acquired orders of magnitude faster than the scanning probe techniques. Furthermore, a confocal setup permits tomography, which is extremely limited in the scanning probe techniques due to their surface nature.
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T. J. Huffman, Robert Furstenberg, Christopher A. Kendziora, and R. A. McGill "Infrared spectroscopy below the diffraction limit using an optical probe", Proc. SPIE 10657, Next-Generation Spectroscopic Technologies XI, 106570O (14 May 2018);

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