Off-Axis Digital Holographic Microscope With A Rotating Diffraction Plate For Speckle Suppression

Off-axis digital holographic microscopy (DHM) is a technique that can convert a single image, called hologram, into a 3D volume. A hologram encodes the phase and intensity information of the samples. Through post-processing, it can be used to reconstruct the quantitative phase map and track the spatial position of multiple samples. The temporal resolution is only limited by the acquisition speed of the camera. These unique features have been applied to studying sperm motility and bacterial dynamics. The phase information is encoded by the coherence fringes in the hologram and hence inevitably suffers from speckle noise of the laser. To suppress this speckle noise, we mounted a diffraction plate in front of the laser. The plate rotates at the velocity greater than the acquisition speed of the camera creating a time averaged hologram. The addition of the rotating diffraction plate significantly reduces the speckle noise, in turn mitigating errors during phase map reconstruction. We show here how this approach improves image quality and the reconstruction process and the ease with which it can be implemented in an open-frame DHM platform.