Vertical Microscope Based on Parallel Phase-Shifting Digital Holography

The authors present an optical microscope based on parallel phase-shifting digital holography. The microscope was constructed on an optical breadboard standing vertical to an optical table. In this microscope, a high-speed polarization-imaging camera was employed to record four phase-shifted holograms with a single-shot exposure. This camera can record intensities of four linearly-polarized light waves contained in the incident light wave to the image sensor by every $2 \times 2$ pixels. As the magnification optical system in this microscope, an afocal optical system was employed in order that the lateral and longitudinal magnifications of the optical system are independent of the depth position of an object. The microscope was designed so as to be a transmission microscope to measure three-dimensional (3D) shape or 3D behavior of transparent specimens such as live cells. Besides, the microscope was designed as an inverted microscope, in which the specimen is irradiated by the illumination light from above. The authors recorded the transparent gas blasted from the syringe, as the first demonstration for a dynamic transparent object at the rate of 1000 frames per second (fps). The transparent gas consisted of carbon dioxide and dimethyl ether. Phase delay by blasting gas flow were successfully recorded and reconstructed by the microscope. Thus, high-speed motion-picture of phase of a dynamic minute object was experimentally demonstrated by the microscope.