Raman Imaging and Raman Mapping - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 94

5
Raman Imaging and Raman Mapping
Francis W.L. Esmonde-White and Michael D. Morris
Abstract Raman spectroscopy can be used to non-destructively add image con-
trast in visualizing structures and dynamics in living systems and materials. Image
contrast can be derived from any information contained in Raman spectra, including
band intensities, positions and widths. Because these parameters are functions of
the local physical and chemical environment of a constituent, the images can dis-
play these properties as well. This chapter discusses instrumentation for acquiring
low definition Raman maps and high definitions Raman images in two and three
dimensions. Experimental configurations and their advantages and drawbacks are
described. Methods for enhancing resolution are discussed. Finally several examples
these techniques are presented, with an emphasis on application areas not elsewhere
discussed in the topic.
5.1 Introduction
Raman spectroscopy can be used to construct images, whose contrast is based
on any sample property directly or indirectly contained in the spectrum. In
this chapter, instrumentation for Raman imaging is reviewed, along with se-
lected recent developments. Methods for the analysis of Raman images are
described in Chap. 8 and will not be repeated here. The two major uses of
Raman imaging are for determining relative chemical composition and clas-
sification. Chemical composition is most commonly used to provide contrast
for determining spatial distributions of chemical components (as shown in
Figs. 5.3 and 5.4). The intensity at any pixel in the image is proportional to
the amount of component at the point corresponding to that pixel. Similarly,
the intensity ratio of two components can also be used to determine a relative
composition. Some of the physical properties that influence the spectrum of
a component can also be used to generate contrast. Important examples in-
clude lattice strain and component orientation. Further chemical and physical
properties can be detected through parameters such as the center of gravity,
area, and width of Raman bands.