arXiv subjects

Martín Molezuelas-Ferreras

Publications and source records attributed to Martín Molezuelas-Ferreras.

4 recordsLinked to original sources

arXiv2026

Characterizing the Backscattered Spectrum of Mie Spheres

This study describes both experimentally and theoretically an important hitherto undiscovered feature of the scattering of micron_sized spherical objects when illuminated with highly focused circularly polarized light. This is a regime of high experimental relevance which has not been described in full detail. The experiments are complemented with the analytical formulas explaining the field scattered directed toward the backward hemispace. In particular, it is proven that this field shows a very regular oscillatory dependency with the optical size. This phenomenon is typically hidden in the total scattered field, as the field is scattered much less toward the backward hemisphere than toward the forward one. These regular oscillations are measured experimentally. It is proven that, by analyzing them, it is possible to determine the index of refraction of isolated micron_sized particles, opening new paths for applications in sensing and metrology.

physics.optics↗

arXiv2026

Optical forces, helicity, angular momentum and how they are all intertwined

The theoretical description of optical forces and torques on micron_sized particles is a crucial area of research and has formed the foundation for advancements in optical trapping and manipulation technologies. In this study, we derive analytical expressions for optical forces and torques on micron_sized spherical particles illuminated by focused Laguerre_Gaussian (LG) beams, employing the well_defined helicity multipolar decomposition of electromagnetic fields and Mie theory. We developed a multifunctional program, Multipolar Optical Forces Toolbox, based on this theoretical framework. The program, available on GitHub, was used to generate optical trapping stability maps. These maps predict trap stability across a wide range of system parameters and serve as a practical tool for designing advanced optical trapping experiments. Our analysis reveals the important role of helicity p and orbital angular momentum l on the dynamics of particles trapped off_axis in LG beams and demonstrates the unique nature of the tangential torque. Our findings also highlight notable differences in longitudinal optical forces resulting from pure helicity modifications in Gaussian beams. Furthermore, we showcase the ability of LG beams to isolate Mie resonances, offering a novel approach to locate the spectral positions of the resonances of high multipolar modes. These insights deepen the understanding of helicity in LG optical traps and pave the way for the development of more advanced optical manipulation techniques.

physics.optics↗

arXiv2026

On-Axis Optical Trapping with Vortex Beams: The Role of the Multipolar Decomposition

Optical trapping is a well_established, decades old technology with applications in several fields of research. The most common scenario deals with particles that tend to be centered on the brightest part of the optical trap. Consequently, the optical forces keep the particle away from the dark zones of the beam. However, this is not the case when a focused doughnut_shaped beam generates on_axis trapping. In this system, the particle is centered on the intensity minima of the laser beam and the bright annular part lies on the periphery of the particle. Researchers have shown great interest in this phenomenon due to its advantage of reducing light interaction with trapped particles and the intriguing increase in the trapping strength. This work presents experimental and theoretical results that extend the analysis of on_axis trapping with light vortex beams. Specifically, in our experiments, we trap micron_sized spherical silica (SiO2) particles in water and we measure, through the power spectrum density method, the trap stiffness constant \k{appa} generated by vortex beams with different topological charge orders. The optical forces are calculated from the exact solutions of the electromagnetic fields provided by the generalized Lorentz_Mie theory. We show a remarkable agreement between the theoretical prediction and the experimental measurements of \k{appa}. Moreover, our numerical model gives us information about the electromagnetic fields inside the particle, offering valuable insights into the influence of the electromagnetic fields present in the vortex beam trapping scenario.

physics.optics↗

arXiv2021

Bandwidth control of the biphoton wavefunction exploiting spatio-temporal correlations

In this work we study the spatio-temporal correlations of photons produced by spontaneous parametric down conversion. In particular, we study how the waists of the detection and pump beams impact on the spectral bandwidth of the photons. Our results indicate that this parameter is greatly affected by the spatial properties of the detection beam, while not as much by the pump beam. This allows for a simple experimental implementation to control the bandwidth of the biphoton spectra, which only entails modifying the optical configuration to collect the photons. Moreover, we have performed Hong-Ou-Mandel interferometry measurements that also provide the phase of the biphoton wavefunction, and thereby its temporal shape. We explain all these results with a toy model derived under certain approximations, which accurately recovers most of the interesting experimental details.

quant-ph↗