Direct imaging Raman microscope based on tunable wavelength excitation and narrow band emission detection

A new type of imaging Raman microscope is described. First the advantages and disadvantages of the two possible approaches to Raman microscopy based on signal detection by means of a charge-coupled-device camera (i.e., direct imaging and image reconstruction) are discussed. Arguments are given to show that in most cases direct imaging is to be preferred over image reconstruction, because it provides the desired information in less time. In the direct imaging Raman microscope presented in this communication, detection of scattered light occurs in a narrow interval around a fixed wavelength. Selection of the Raman wavenumber shift at which an image is recorded is established by tuning the wavelength of the exciting laser light in such a way that the wavelength of the Raman scattered light with the desired Raman shift coincides with the detected wavelength. The microscope has been incorporated in a Raman microspectrometer in a way that enables easy switching between the imaging and the multichannel spectroscopy modes of operation. Bright field, fluorescence, and Raman microscopic images can be obtained.