Super-resolved Mirau digital holographic microscopy

A Mirau interferometric objective can be used for common-path and vibration-immune digital holographic microscopy (DHM). However, high-magnification Mirau objectives are expensive and suffer from low working distances, and the commonly used low-magnification Mirau objectives do not have high lateral resolutions. In this paper, we report two different approaches toward enhancing the resolution in Mirau DHM. First, we show that by placing a glass microsphere (MS) within the working distance of a low-magnification Mirau objective, its effective numerical aperture can be increased, leading to super-resolved three-dimensional images. The improvement in the lateral resolution depends on the size and the vertical position of the MS, and by varying these parameters, the lateral resolution and magnification may be adjusted. In the second approach we apply structured illumination toward super-resolved 3D imaging in Mirau DHM. The structured illumination is applied by implementing successive sinusoidal gratings with different orientations, or instead, single 2D gratings, e.g. checkerboard or hexagonal patterns, onto a spatial light modulator. Our results show that with this method an improvement of 35% in the resolution power of the DHM can be achieved. As potential applications the arrangements were used for thalassemia minor red blood cell identification and 3D surface characterization of polymeric nanocomposites. The presented arrangements have the potential to serve as a table-top device for high resolution holographic microscopy.