arXiv subjects

Isael Herrera

Publications and source records attributed to Isael Herrera.

7 recordsLinked to original sources

arXiv2026

Multiparameter estimation for the superresolution of two incoherent sources

We experimentally demonstrate the simultaneous estimation of the three parameters characterizing a pair of incoherent optical sources in the sub-Rayleigh regime, enabling super-resolved scene characterization. Using spatial-mode demultiplexing (SPADE) with two demultiplexers--one deliberately shifted--we determine separations well below the diffraction limit and achieve sensitive joint estimation of separation, centroid, and relative brightness over a broad range of scene configurations in a single experimental setting. We benchmark our performance using Fisher-information-based Cram\'er-Rao bounds, and discuss the corresponding quantum limits. We investigate two complementary scenarios: a realistic case with slightly non-identical sources, and an idealized case of indistinguishable sources.

quant-ph↗

arXiv2025

3D Stokes polarimetric imaging at nanoscales

Optical fields polarized along three dimensions are frequent in optical microscopy and nanophotonics, and yet retrieving their polarization distribution is challenging. We present the experimental implementation of three-dimensional (3D) Stokes polarimetric imaging of nonparaxial optical fields with nanoscale spatial resolution. This approach extends classical Stokes polarimetry (traditionally limited to paraxial fields) into the nonparaxial regime. We use an array of gold nanospheres, each acting as a localized electric dipolar scatterer, to probe 3D polarization states over a field of view of tens of micrometers. The scattered signal is collected by a high numerical aperture objective lens and separated into its circular polarization components, providing a very simple imaging system. We introduce a computational algorithm to efficiently extract the physical parameters from the generated dipole spread functions with a high throughput across the whole field of view. Finally, we show that this method can also be applied to single-molecule localization and orientation fluorescence microscopy.

physics.optics↗

arXiv2024

Propagation-invariant optical meron lattices

We introduce and produce experimentally optical beams exhibiting periodic skyrmionic polarization lattices at each transverse plane of propagation. These textures are meron lattices formed by tiles mapping hemispheres of the Poincaré sphere. All presented fields are combinations of a small number of plane waves. Firstly, we propose square lattices with a Skyrme density (the Jacobian of the mapping between the Poincaré sphere and physical space) that oscillates in sign but whose intensity distribution is constant. Secondly, we present triangular lattices preserving the Skyrme density's sign. Both lattices are invariant under propagation. Finally, we introduce a family of lattices with uniform Skyrme density sign, composed of square tiles that map to the same hemisphere of the Poincaré sphere. In these lattices, the polarization state undergoes a uniform local periodic rotation during propagation, thus preserving the texture's Skyrme density distribution.

physics.optics↗

arXiv2024

Vectorial phase retrieval in super-resolution polarization microscopy

In single molecule orientation localization microscopy, valuable information about the orientation and longitudinal position of each molecule is often encoded in the shape of the point spread function (PSF). This shape, though, can be affected significantly by aberrations and other imperfections in the imaging system, leading to erroneous estimation of the measured parameters. A basic solution is to model the aberrations as a scalar mask in the pupil plane that is characterized through phase retrieval algorithms. However, this approach is not suitable for cases involving polarization-dependent aberrations, introduced either through unintentional anisotropy in the elements or by using birefringent masks for PSF shaping. Here, this problem is addressed by introducing a fully vectorial model in which the polarization aberrations are represented via a spatially-dependent Jones matrix, commonly used to describe polarization-dependent elements. It is then shown that these aberrations can be characterized from a set of PSF measurements at varying focal planes and for various polarization projections. This PZ-stack of PSFs, which contains both phase and polarization projection diversity, is used in a phase retrieval algorithm based on nonlinear optimization to determine the aberrations. This methodology is demonstrated with numerical simulations and experimental measurements. The pyPSFstack software developed for the modeling and characterization is made freely available.

physics.optics↗

arXiv2023

Periodic skyrmionic textures via conformal cartographic projections

We find periodic skyrmionic textures via conformal cartographic projections that map either an entire spherical parameter space or a hemisphere onto every regular polygon that provides regular tessellations of the plane. These textures minimize the energy inherent to the mapping and preserve the sign of the Skyrme density throughout the entire space. We show that 2D spinor fields (e.g., 2D polarization) that present periodic textures preserving the sign of the Skyrme density, unavoidably exhibit zeros. We implement these textures in the polarization state of a laser beam.

physics.optics↗

arXiv2022

Using fluorescent beads to emulate single flurophores

In this work, we study the conditions under which fluorescent beads can be used to emulate single fluorescent molecules in the calibration of optical microscopes. Although beads are widely used due to their brightness and easy manipulation, there can be notable differences between the point spread functions (PSFs) they produce and those for single-molecule fluorophores, caused by their different emission pattern and their size. We study theoretically these differences for various scenarios, e.g. with or without polarization channel splitting, to determine the conditions under which the use of beads as a model for single molecules is valid. We also propose methods to model the blurring due to the size difference and compensate for it to produce PSFs that are more similar to those for single molecules.

physics.optics↗

arXiv2022

Simple computer program to calculate arbitrary tightly focused (propagating and evanescent) vector light fields

In this work we present a simple code to calculate tightly focused vectorial light fields (propagating and evanescent) generated by input fields that have arbitrary amplitude, phase and polarization. The program considers results from previous studies, like integration via fast Fourier transforms to speed up the integration. The calculations are done in a Cartesian coordinate system that is convenient to compare with experimental results for beams that are shaped with programmable optical elements like spatial light modulators or digital micromirror arrays. We also discuss how to avoid diverging terms at the origin by shifting the angular mesh by half a point and correcting the output by cancelling the phase term that arises from the shifted Fourier transform.

physics.optics↗