Differential Interference Contrast (DIC)
DIC in incident light
This method, an extension of polarization contrast, is suitable for the visualization of even minute differences in height on surfaces. A birefringent prism (4) is used which splits the polarized light beam into two partial beams on its way to the sample. These two partial beams strike the sample (6) with lateral displacement from each other. If the surface is completely flat, nothing will happen. However, if there is a small step between the partial rays, one of the two beams has to travel along a path which is 2 delta h longer and receives this path difference. Once the partial beams have returned via DIC prism (4) and analyzer (7), they display the same direction of vibration again – due to the
|analyzer – and can interfere with each other in the intermediate image. The path difference experienced on the surface then changes into gray values which can be seen by the eye: steps become visible in the form of relief. As an auxiliary object, the lambda-plate (7a) finally changes the gray values into colors again.|
The structure of this brass specimen can only be seen very faintly in incident-light brightfield.
The same sample surface appears to have three-dimensional relief in DIC.
|Altough the KTH NanoFabLab microscope is not equipped with a DIC option for transmitted light there is a similar description of that here.|