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| Reflected-light – Differential Interference Contrast (DIC) |
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As an extension of polarization contrast, this method also allows the visualization of minute elevation differences in surfaces.
A birefringent prism (4) is used, which splits the polarized light beam into two partial beams on its way to the sample. These partial beams hit 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 two partial beams, one of the two beams must travel a path which is 2Δh longer and is assigned this path difference.
Once the partial beams have returned via the DIC prism (4) and the analyzer (7), they feature the same vibration direction again – due to the analyzer – and can interfere with each other in the intermediate image. The path difference assigned on the surface then changes into grey values which can be seen by the eye: steps become visible as a relief. As an auxiliary object, the lambda plate (7a) changes the grey values into colors again.
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| The structure of this brass sample can be seen only very faintly in reflected-light brightfield. | The same sample surface looks like a three-dimensional relief image in Differential Interference Contrast (DIC). |
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