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Lensless inline digital holography versus Fourier ptychography: phase estimation of a large transparent bead

Abstract. Lensless inline digital holographic microscopy (LI-DHM) and Fourier ptychographic microscopy (FPM) are two widespread quantitative phase imaging (QPI) techniques. They have been employed in various fields, especially for biological slice imaging because of their simplicity in use, stability in structure, and also large field of view. Spherical phase response (for example from HeLa cells) is commonly observed in biological imagery. As a consequence, for calibration and validation purposes, small (several to tenth of microns in diameter) transparent microbeads have been used as standards. Phase imaging of their large counterparts (hundreds of microns in diameter) using either LI-DHM or FPM has not been reported so far. We are aiming to analyze the phase response of a 146-μm soda-lime microsphere. It has been immersed in Canada balsam to reduce phase difference and to avoid overexposed diffraction rings. The phase estimation issue has been tackled using approaches that involve either Gerchberg–Saxton type algorithms or an inverse problem-based procedure. Confronting the results confirms the QPI capability for both imaging techniques to assess phase responses from such a large transparent object.