Three-dimensional chemical imaging with a confocal scanning laser Fourier transform-Raman microscope

Traditional approaches in confocal microscopy have focussed on techniques that use elastically, or Rayleigh, scattered photons to generate volumetric intensity or phase images of an object. Common to these imaging modes is an inability to discriminate between optically similar but chemically distinct materials. We report in this paper on a new class of confocal microscope which uses inelastically, or Raman, scattered light to generate volumetric chemical images of a material. We designed and built a prototype instrument, called a confocal scanning laser FT-Raman microscope, which combines a confocal scanning laser microscope with a FT Raman spectrometer. The high depth and lateral spatial resolution of the confocal optics design defines a volume element from which the Raman scattered light is collected and then analyzed by the spectrometer for its spectral content. The sample is scanned through the microscope focal volume and a 3D chemical image is generated based on the content of the Raman spectrum measured at each scan position. The results to be presented include instrument characterization measurements and examples of volumetric chemical imaging.