Determining Spatial Resolution in Raman Spectral Imaging – What is Different from Optical Microscopy Imaging

Abstract

Raman microscopy is a hybrid technique between Raman spectroscopy and microscopy. Raman microscopes using optical microscopes were introduced in the 1970's, and take advantage of diffraction-limited optics to provide molecular and crystalline information. The spatial resolution of a Raman microscope is reported to be the order of the laser wavelength [1, 2]. A Raman microscope equipped with a automated stage records Raman maps using the point mapping method, which is, so far, the most popular method to record Raman maps. Successful data processing of Raman spectra within a Raman map results in Raman images that represent spatial/volumetric distribution of different chemical components within the sample. Since Raman images are distillations of spectral information, the spectral quality (e.g. signal-to-noise ratio) is directly correlated to the image quality [3]. Also, the spectral differences between two point measurements (chemical contrast) are directly correlated to the resolving power between two points, which influences the spatial resolution [4]. As a result, the spatial resolution in Raman Imaging must be determined differently from that of optical (?) microscopy.