Near-field Raman Imaging is a combined microscopy technique that links chemical Raman information to high resolution Scanning Near-field Optical Microscopy (SNOM). It allows the acquisition of high-resolution confocal Raman images. Lateral resolutions of down to 60 nm can be achieved.
The near-field Raman imaging principle
The excitation laser light is focused through the SNOM-tip resulting in an evanescent field (near-field) on the far side of the aperture. While the sample is moved on a piezo-driven scan stage, the transmitted light is spectroscopically detected point by point and line by line in order to generate a hyperspectral image. The optical resolution of the transmitted light is limited only by the diameter of the aperture (down to 60 nm).
Using a beam deflection setup as in AFM contact mode, it is ensured that the cantilever is always in contact with the sample. In this way the topography is recorded simultaneously along with the Near-field Raman measurement.