DarkFocus: numerical autofocusing in digital in-line holographic microscopy using variance of computational dark-field gradient
Abstract We report on a novel computational technique for automatic numerical refocusing in digital in-line holographic microscopy. It is based on the adaptive filtering of the recorded on-axis hologram to eliminate its background term and extract interference intensity-component connected with light scattered on the sample (interference fringes). Numerical propagation of such filtered hologram yields the computationally generated dark-field imaging coming from the amplitude part of the complex field. We propose a simple measure in the form of the variance of the dark-field gradient, which attains its maximum value in the focal planes for all types of objects (phase, amplitude and mixed pha…
Dual-mode holographic microscopy imaging platform
We report on a novel layout capable of dual-mode imaging in real time with different magnifications and resolution capabilities in lensless microscopy. The concept is based on wavelength multiplexing for providing two illuminations with different wavefront curvatures: one is collimated, allowing a large field of view (FOV) with a poor resolution limit, and the other is divergent, to achieve a better resolution limit (micron range) over a small FOV. Moreover, our recently reported concept of MISHELF microscopy [M. Sanz, J. Á. Picazo-Bueno, L. Granero, J. García and V. Micó, Sci. Rep., 2017, 7, 43291] is applied to the divergent illumination case, improving the image quality by noise averagin…
Single-shot two-frame π-shifted spatially multiplexed interference phase microscopy
Single-shot, two-frame, π-shifted spatially multiplexed interference microscopy (π-SMIM) is presented as an improvement to previous SMIM implementations, introducing a versatile, robust, fast, and accurate method for cumbersome, noisy, and low-contrast phase object analysis. The proposed π-SMIM equips a commercially available nonholographic microscope with a high-speed (video frame rate) enhanced quantitative phase imaging (QPI) capability by properly placing a beam-splitter in the microscope embodiment to simultaneously (in a single shot) record two holograms mutually phase shifted by π radians at the expense of reducing the field of view. Upon subsequent subtractive superimposition of hol…
Upgrading a brightfield optical microscope into a robust numerically advanced interference-based phase imager
The approach to convert a brightfield microscope into an interference-based versatile quantitative phase imaging unit is presented. It employs partially coherent illumination and diffraction grating. Enhanced interferogram bio-phase retrieval is performed by two-shot numerically-robust Hilbert-Huang method.
Single-shot slightly off-axis digital holographic microscopy with add-on module based on beamsplitter cube
Slightly off-axis digital holographic microscopy (SO-DHM) has recently emerged as a novel experimental arrangement for quantitative phase imaging (QPI). It offers improved capabilities in conventional on-axis and off-axis interferometric configurations. In this contribution, we report on a single-shot SO-DHM approach based on an add-on module adapted to the exit port of a regular microscope. The module employs a beamsplitter (BS) cube interferometer and includes, in addition, a Stokes lens (SL) for astigmatism compensation. Each recorded frame contains two fields of view (FOVs) of the sample, where each FOV is a hologram which is phase shifted by π rads with respect to the other. These two …