Infrared spectroscopic chemical imaging

Abstract

Infrared (IR) spectroscopy is a powerful, widely used technique for identifying materials or chemical compounds. An IR spectrum often provides a specific fingerprint for a given molecular component or species. IR frequencies, intensities, and line widths are also extremely sensitive to environmental perturbations and changes in molecular structure. Infrared spectroscopic images recorded through a Fourier transform infrared (FT-IR) microscope attachment have traditionally been constructed by translating a mapping stage a single pixel at a time through the sample area of interest; this is a very tedious and time-consuming procedure. Recently, a technique for rapidly performing high-fidelity FT-IR imaging spectroscopy using an indium antimonide (InSb) focal-plane array (FPA) detector coupled to an IR microscope and a step-scanning FT-IR spectrometer has been developed. These multichannel IR detectors were originally developed for thermal-imaging applications (mainly in the military), but they have tremendous potential as chemical imaging detectors when used as part of a spectrometer. The multiple detector elements enable images from all pixels to be collected simultaneously for each mirror retardation position of the interferometer. Use of an interferometer allows the entire IR spectrum over some wavelength range to be measured. The combination of a step-scanning FT-IR microscope and an InSb FPA detector provides unprecedented speed and image quality, limited only by the diffraction limit and/or the number of detector elements on the array.