Diffraction phase microscopy: principles and applications in materials and life sciences

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The main obstacle in retrieving quantitative phase with high sensitivity is posed by the phase noise due to mechanical vibrations and air fluctuations that typically affect any interferometric system. In this paper, we review diffraction phase microscopy (DPM), which is a common-path quantitative phase imaging (QPI) method that significantly alleviates the noise problem. DPM utilizes a compact Mach–Zehnder interferometer to combine several attributes of current QPI methods. This compact configuration inherently cancels out most mechanisms responsible for noise and is single-shot, meaning that the acquisition speed is limited only by the speed of the camera employed. This technique is also nondestructive and does not require staining or coating of the specimen. This unique collection of features enables the DPM system to accurately monitor the dynamics of various nanoscale phenomena in a wide variety of environments. The DPM system can operate in both transmission and reflection modes in order to accommodate both transparent and opaque samples, respectively. Thus, current applications of DPM include measuring the dynamics of biological samples, semiconductor wet etching and photochemical etching processes, surface wetting and evaporation of water droplets, self-assembly of nanotubes, expansion and deformation of materials, and semiconductor wafer defect detection. Finally, DPM with white light averages out much of the speckle background and also offers potential for spectroscopic measurements.