Imaging mechanisms analysis of compact digital holographic microscope for microparticles measurement

Conventional optical microscopy suffers from small depth of focus due to its high numerical aperture and magnification of the microscope objective. In comparison, digital in-line holographic microscopy (DIHM) provides information about the entire 3D volume through numerical reconstruction of the single hologram at several depths. This advantage makes DIHM an effective tool for the measurement of microparticles in suspension. Recently, our group has demonstrated the potential of DIHM for accurate measurement of particles with sizes ranging from 40 microns to a few millimetres. In this paper, the applicability of DIHM is extended for measurement of near-micron sized particles. A compact digital holographic microscope with a single microscope objective is presented. The system imaging mechanisms of the microscope is analyzed first and the recording distance of digital hologram is calculated using spatial frequency analysis. Then the system magnification, lateral resolution and depth resolution are analyzed in terms of the hologram recording distance. Finally, the characterization of microparticles with a diameter of 1 micron and 10 microns is demonstrated with the compact setup. The experimental results show the efficiency and accuracy of this method with a measured error less than 1.55% in the diameter of certified particles.