Figure 2
Natural barite (BaSO4) ore sample, ground in a mortar and pestle, was mostly transparent grains with a fair number of pink/red components. Analysis by powder X-Ray diffraction indicates the presence of other minerals such as quartz and cerusitte (PbCO3). Grains were placed on a coverslip and a drop of cyanacrylate glue was added on top, then placed on a slide. The cyanoacrylate was allowed to cure for about 1 hour before imaging. Laser conditions were 40 mW at 943 nm and 20 mW at 1040 (modulated). (a) The strong backward propagating signal (shown in red) spatially overlaps, consistently, with the red colored grains in the sample, whereas the forward-collected SRS signal (shown in cyan) is tuned to the sulfate Raman resonance of BaSO4 at 985 cm−1. Volume is 205 × 205 × 40 microns into a 256 × 256 × 40 voxel data set. Focal slices were collected at 1 micron intervals. The total data collection time was about 90 s. (b) 2D image of the Raman spectral scan of the region of interest (red oval), confirms the BaSO4 Raman resonance at 985 cm−1, shown in (c).
