Physical phase compensation in digital holographic microscopy

Abstract

In digital holographic microscopy (DHM), using microscope objective for sample imaging may introduce additional spherical phase curvature. It can be physically compensated by introducing a same phase curvature in the reference beam. A theoretical analysis of the wavefront interefence between the reference beam and object beam is provided to indicate the physical phase compensation. The spatial frequency spectra of the hologram are involved for the judgement of the physical phase compensation status. Different DHM setups are presented in order to fulfill the physical compensation of the introduced spherical phase. In the DHM setups based on the Michelson interferometric configuration, an adjustable lens is used to perform the quasi physical phase compensation during the hologram recording. In the common-path DHM setups, digital off-axis holograms are recorded by using a single cube beam splitter in a non-conventional configuration so as to both split and combine a diverging spherical wavefront emerging from a microscope objective. A simple plane numerical reference wavefront is used for the reconstruction and the correct quantitative phase map of the test object is obtained after phase unwrapping. Its simplicity of the presented setups make it easy to be well aligned and with lower cost.