At its best, one of the key benefits of coherent Raman imaging is the ability to perform chemically specific imaging without any sample preparation. Here we show two of such examples: 1) a water based body lotion where different immiscible oily components highlight as droplets in different colours (above), and 2) a surface image of a prescription free melatonin tablet showing the distribution of the ingredients (below).
As in any spectroscopic technique, the chemical specificity stems from the distinct spectra of the components, which the instrument can resolve and visualize with different colours. Visualization can take place in various ways, such as the intrinsic colour mapping from visible to the infrared as in our previous post (Colours of infrared). Another option is to use a multivariate analysis technique. Here, the example is based on simple classical least squares (CLS) analysis. The pure component spectra of the sample are identified and used to calculate the combination that minimizes error of observation to the model in a least squares sense at each pixel. As on outcome, one obtains intensity maps for each pure component, which can be coloured in a preferred way and combined to form a chemically specific image of the sample, as in the figure below.