<title>Raman imaging microscopy: a novel chemical imaging technique</title>

Abstract

We describe a Raman imaging microscope that produces high-fidelity, large format Raman images and Raman spectra at close to diffraction-limited spatial resolution. A silicon charge- coupled device is used as a high sensitivity array detector. Wavelength selection of Raman scattered emission is achieved by an acousto-optic tunable filter, which maintains image fidelity and provides either continuous or random wavelength selection. Laser illumination is delivered to the object by means of an infinity corrected microscope objective, either by a galvanometer scanning system or a widefield fiber optic. The laser scanning mechanism has higher power densities and provides Raman microprobe capabilities when stopped at a prescribed point. The fiber optic illumination scheme, however, is useful for delicate samples which might be damaged by the higher power densities generated by the point scanner mechanism and for sample alignment and system focusing. Instrument features, including factors that determine the system's spatial and spectral resolution, are discussed in detail. Images and spectra of test objects and samples that demonstrate the capabilities of this imaging spectrometer are presented. The potential of intrinsic chemical imaging is discussed in terms of its use in the analyses of a variety of chemical and biological samples.