Real-time digital holographic microscopy

A multi-camera implementation of the in-line phase-shifting digital holographic microscopy is a straightforward solution for real-time measurement. The work presents a portable phase-stepping holographic microscope for measurement in a real time operation mode. The interferometric system is based on a parallel arrangement of four Mach-Zehnder interferometers with equalized optical paths. A conventional microobjective-projective optical system is used to form the image in infinity. A set of beam splitters and adjustable polarization filters on the way of the object and reference wavefronts ensure the same contrast of fringe patterns in the plane of CCD targets. High precision of the phase shift in every interferometer is achieved by incorporation of highly accurate optical retarders. The registration module consists of four monochrome CCD cameras and a color camera for simultaneous recording of four phase shifted monochrome images together with a color image in white light. The laser source is CIF or pulse generating DPSS laser at 532 nm wavelength which is suitable for investigation of leaving cells by 3D imaging and fluorescence analysis. Taking in view the pointwise nature of the phase-shifting. technique, a modified algorithm for phase retrieval is derived. The algorithm requires preliminary calibration of the system by a phase-stepping interferometric measurement in each channel. The calibration allows for compensation of errors induced by the misalignments between the object and reference wavefronts. The modeling of the system performance and error analysis confirm its reliable behavior without imposing drastic restrictions on system alignment. Some experimental verification is also provided.