Abstract: Despite the widespread exploration and application of digital lensless holographic microscopes (DLHMs), there remains a scarcity of portable implementations tailored specifically for fieldwork applications such as remote diagnosis, medical analysis, on-field biological sample study, and even outreach and academic demonstrations. This paper introduces a portable prototype that assembles a digital lensless holographic microscope (DLHM) with a smartphone camera designed specifically for such fieldwork scenarios. The prototype incorporates a customized illumination system, based on a freeform lens, enhancing efficiency and simplifying alignment. A 3D-printed tube houses all components, facilitating easy alignment adjustments by incorporating two axes that keep the optical axis aligned. The design replaces conventional scientific camera sensors with the digital sensor of smartphone cameras. The customized mechanical coupling accommodates the specific light source, and an off-the-shelf microscope and telescope adapter (GoSky) ensures seamless cellphone attachment. The portable freeform-based DLHM assembly requires only a few components, with precise CAD design guiding the production of five 3D-printed parts. The resulting DLHM is compact, measuring 13.6 cm in height, 5 cm in diameter, and weighing about 250 grams. This approach successfully employs the digital sensor of a HUAWEI P8 Lite smartphone after removing its camera lens to ensure free space propagation to the sensor. The system allows recording holograms with variable magnification ranging from 1× to 20× approximately, with a maximum numerical aperture (NA) of 0.12 and resolution of 1.71 µm. To validate the performance of this portable DLHM system, imaging experiments are conducted using a USAF resolution test target and a buccal mucosa sample containing epithelial cheek cells. This study underscores the practicality of the proposed DLHM system for fieldwork applications.

Abstract: The normalized cross-correlation ( N C C ) is widely used for image registration due to its simple geometrical interpretation and being feature-agnostic. Here, after reviewing N C C definitions for images with an arbitrary number of dimensions and channels, we propose a generalization in which each pixel value of each channel can be individually weighted using real non-negative numbers. This generalized normalized weighted cross-correlation ( N W C C ) and its zero-mean equivalent ( Z N W C C ) can be used, for example, to prioritize pixels based on signal-to-noise ratio. Like a previously defined N W C C with binary weights, the proposed generalizations enable the registration of uniformly, but not necessarily isotropically, sampled images with irregular boundaries and/or sparse sampling. All N C C definitions discussed here are provided with discrete Fourier transform ( D F T ) formulations for fast computation. Practical aspects of N C C computational implementation are briefly discussed, and a convenient function to calculate the overlap of uniformly, but not necessarily isotropically, sampled images with irregular boundaries and/or sparse sampling is introduced, together with its D F T formulation. Finally, examples illustrate the benefit of the proposed normalized cross-correlation functions.

Abstract: We report electromagnetic field modes solving the inhomogeneous Maxwell equations for parabolic gradient index fibers in the low refractive index contrast approximation. The first family comprises accelerating fields characterized by an intensity distribution center tracing a circular trajectory transverse to the fiber optical axis. These fields maintain an invariant shape for both their intensity and phase distributions while rotating around their center. The second family comprises breathing fields characterized by an intensity distribution center aligned with the fiber optical axis. These fields exhibit intensity distribution scaling along propagation, while their phase swirls and rotates around the optical axis without changing their intensity distribution shape and topological charge.

Abstract: We investigate the radiation generated by a current loop situated within an unbounded uniaxial dielectric-magnetic material characterized by a uniform current distribution. We employ dyadic Green functions in the frequency domain to derive closed-form expressions for the far-field radiation. Our analytical findings distinguish between two scenarios: one in which the loop’s axis aligns parallel to the optic axis and another where it is perpendicular to the optic axis. In cases where the loop’s axis parallel’s the optic axis, only magnetically extraordinary wave is emitted as a consequence. However, when the loop’s axis is perpendicular to the optic axis, both electrically and magnetically extraordinary waves are emitted. Our results demonstrate a pronounced dependence of the radiation pattern on the loop’s size, as observed for various loop radii.