A successful application of self-interference digital holographic microscopy in combination with a sample-rotation-based tomography module for three-dimensional (3-D) label-free quantitative live cell imaging with subcellular resolution is demonstrated. By means of implementation of a hollow optical fiber as the sample cuvette, the observation of living cells in different 3-D matrices is enabled. The fiber delivers a stable and accurate rotation of a cell or cell cluster, providing quantitative phase data for tomographic reconstruction of the 3-D refractive index distribution with an isotropic spatial resolution. We demonstrate that it is possible to clearly distinguish and quantitatively analyze several cells grouped in a "3-D cluster" as well as subcellular organelles like the nucleoli and local internal refractive index changes.

A tunable graphene-based hyperbolic metamaterial is designed and numerically investigated in the mid-infrared frequencies. Theoretical analysis proves that by adjusting the chemical potential of graphene from 0.2 eV to 0.8 eV, the reflectance can be blue-shifted up to 2.3 µm. Furthermore, by modifying the number of graphene monolayers in the hyperbolic metamaterial stack, we are able to shift the plasmonic resonance up to 3.6 µm. Elliptic and type II hyperbolic dispersions are shown for three considered structures. Importantly, a blue/red-shift and switching of the reflectance are reported at different incident angles in TE/TM modes. The obtained results clearly show that graphene-based hyperbolic metamaterials with reversibly controlled tunability may be used in the next generation of nonlinear tunable and reversibly switchable devices operating in the mid-IR range.

We propose a novel tomographic measurement approach that enables a noise suppressed characterization of microstructures. The idea of this work is based on a finding that coherent noise in the input phase data generates an artificial circular structure whose magnitude is the highest at the centre of tomographic reconstruction. This method decreases the noise level by applying an unconventional tomographic measurement configuration with an object deliberately shifted with respect to the rotation axis. This enables a spatial separation between the reconstructed sample structure and the area of the largest refractive index perturbations. The input phase data defocusing that is a by-product of the introduced modification is numerically corrected with an automatic focus correction algorithm. The proposed method is validated with simulations and experimental measurements of an optical microtip.

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