Quantitative phase imaging by pupil modulation different phase contrast (PMDPC)

Abstract

Differential phase contrast (DPC) is a non-interference quantitative phase imaging method achieved by asymmetric optical systems. Quantitative DPC images are achieved previously with asymmetric illumination systems. However, it works well for on-focus thin samples only. Considering the limitation, we develop a pupil modulation differential phase contrast (PMDPC) imaging method. Instead of modulating the illumination, we use a spatial light modulator (SLM) to modulate a 4f imaging system's pupil plane. When half of the pupil plane is blocked by the SLM, a phase gradient image forms on the image plane. Using two such phase gradient images captured separately by applying complementary half-circle pupils on SLM, a DPC image can be constructed that carries the sample's phase information. A quantitative phase image of the sample can be reconstructed after a deconvolution procedure. Further, we are able to combine this quantitative phase with the sample's intensity image to obtain the complete complex object field which then allows us to post-process the image. We report experimentally that aberrations arising from the optical elements in the system can be corrected by deconvolving the reconstructed image with a pre-calibrated pupil function. We can also digitally extend the depth of field using angular spectrum propagation algorithm. With our PMDPC imaging setup where NA equals to 0.36, a quantitative phase image with periodic resolution of 1.73µm is obtained. The depth of field for a 20x, 0.4NA objective is extended digitally by 20 times to -50~50 micrometers.

Additional details