Phase contrast techniques (Zernike, Nomarski, DPC) provide images that are similar to the derivative of the phase of objects.

Visual analysis of these images can lead to interpretation errors. The example below shows the image of DPC of a grid of micro-cuvettes etched in a silica slide:
DPC image of a grid of micro-cuvettes (left) and intensity cross-section (right).
Phase image of a micro-cuvette grid (left) and intensity cross section (right).
The OQaPI software allows to reconstruct phase images from 4 relief images recorded with µLight. OQaPI can be used in combination with the free ImageJ software as a plugin:
Depending on the reconstruction choices, OQaPI provides:

  • QPI: phase images in a stack;
  • DPC: a differential phase contrast image;
  • BF: a super-resolved brightfield image.
Example of images returned by OQaPI and their use with ImageJ.
The information contained in the different images is complementary and can be used jointly. For example, the images opposite represent a grain of colored pollen and observed by bright field (A) and by phase imaging (B) with OQaPI.

For this example, we have an unambiguous decomposition of absorption and phase.

The high color quality of the bright field image makes it possible to identify the regions which have retained the dye.

The spatial resolution of the phase image is very high and makes possible to locate details that are very difficult to detect in the bright field image.
The combination of the two techniques makes possible to extract more information from the same sample than the conventional brightfield observation only .