Topographic confocal Raman imaging enables 3D chemical characterization on rough, inclined or irregularly-shaped samples and can be carried out precisely along or at a set distance from a surface without requiring sample preparation.
The topographic sensor operates according to the confocal chromatic sensor principle: A white-light point source is focused onto the sample with a lens system that has a strong linear chromatic error (hyperchromatic lens system). Every color has therefore a different focal distance. The light reflected from the sample is focused through a pinhole onto a dedicated spectrometer on top of the sensor. As only one specific color is in focus at the sample surface, only this light can pass through a confocal pinhole. The detected wavelength is therefore directly related to the surface topography.
Scanning the sample in the x-y-plane reveals a topographic map of the sample. With this map the sample's surface can be kept in focus during the entire measurement procedure, irrespective of its topography.
The optical sensor controls the distance between the objective and the sample surface with sub-micrometer precision. Thus, any variation occurring during measurements with long integration times is compensated for, resulting in sharp and detailed images.