arXiv subjects

Iker Gómez-Viloria

Publications and source records attributed to Iker Gómez-Viloria.

8 recordsLinked to original sources

arXiv2026

Upper bound to optical forces through the multipolar control of optical beams

Optical tweezers enable the manipulation of microscopic objects using light, yet the fundamental limits to the optical forces that can be exerted on matter remain unknown. Here we derive a general upper bound to the maximum optical force that can be applied to a particle, based on an expansion of electromagnetic fields into well-defined helicity multipolar modes. This method finds the optimal force for any kind of fields external to the particle, including evanescent fields. We apply the method to homogeneous spherical particles in a stable trap and identify the field distributions that saturate this bound for the trapping stiffness. We further provide experimentally accessible strategies to approach these optimal conditions, including configurations using counterpropagating and single-beam traps. Experiments demonstrate a threefold enhancement of trapping forces relative to conventional designs, while theoretical predictions indicate that order-of-magnitude improvements are achievable for larger particles and high angular momentum beams. Our results establish fundamental design principles for maximizing optical forces and define the ultimate limits of optical manipulation.

physics.optics↗

arXiv2026

Controlling the centre of mass motion of levitated particles using structured wavefronts

Optically levitated particles have great potential to form the basis of novel quantum- enhanced sensors. These systems are very well suited for inertial sensing, as the particles are isolated from the environment when they are levitated at low pressures. However, there are many challenges in the experimental realization that may affect the performance of these systems. For example, optical aberrations in the wavefront of the trapping laser which arise from optical elements or misalignment have a great impact on the trapping potential. The detrimental effect of optical aberrations has not been thoroughly studied, and usually they are iteratively corrected, giving some conflicting results depending on the figures of merit that are used. In this work, we present a thorough study of the effects of structuring the wavefront of the trapping beams. We observe that clean beams, i.e. highly focused beams with unaberrated wavefronts, may be used to optimize the longitudinal frequencies, at the cost of the transversal ones. Our work is based in a combination of experimental studies using a complete basis of orthogonal polynomials (Zernike polynomials) to control the wavefront and a set of numerical calculations, which allow us to compare the impact of structured wavefronts on the quality of traps for optically levitated particles in vacuum. This will have direct applications in quantum sensing and fundamental studies of quantum mechanics, as it allows the reduction of optical backaction and thermal decoherence of the particles.

physics.optics↗

arXiv2026

Detection of Hybrid Optical Anapoles in Dielectric Microspheres

Nonradiating optical anapoles are special configurations of charge_current distributions that do not radiate. It was theoretically predicted that, for microspheres, electric and magnetic dipolar coefficients can simultaneously vanish by engineering the incident light, leading to the excitation of nonradiating hybrid optical anapoles. In this work, the experimental detection of hybrid optical anapoles in dielectric microspheres (TiO2) is reported using dual detection optical spectroscopy, developed to enable sequential measurement of forward and backward scattering under tightly_focused Gaussian beam (TFGB) illumination. The results show that the excitation of TiO2 microspheres (diameter, d approx. 1 um) under TFGB illumination leads to the appearance of scattering minima in both the forward and backward directions within specific wavelength ranges. These scattering minima are found to be due to vanishing electric and magnetic dipolar coefficients associated with hybrid optical anapoles. The ability to confine electromagnetic fields associated with hybrid optical anapoles can give rise to several novel optical phenomena and applications.

physics.optics↗

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↗

arXiv2023

Characterizing cylindrical particles upon local measurements of two Stokes parameters

Researchers routinely characterize optical samples by computing the scattering cross-section. However, the experimental determination of this magnitude requires the measurement and integration of the components of the scattered field in all directions. Here, we propose a method to determine the scattering cross-section and global polarization state of radiation through measurements of two Stokes parameters at an angle of choice in far-field. The method applies to cylindrically symmetric samples whose optical response is well-described by a single multipolar order j. Moreover, the formalism is applicable for a wide range of different illuminations, and it only requires the use of a single camera and conventional wave plates. Our findings significantly reduce the complexity of routine characterization measurements for cylindrical samples in optical laboratories.

physics.optics↗

arXiv2023

Capturing near-field circular dichroism enhancements from far-field measurements

Molecular Circular dichroism (CD) spectroscopy faces significant limitations due to the inherent weakness of chiroptical light-matter interactions. In this view, resonant optical antennas constitute a promising solution to this problem since they can be tuned to increase the CD enhancement factor, fCD, a magnitude describing the electromagnetic near-field enhancement of scatterers associated with a given helicity. Here, we derive an exact multipolar expansion of fCD, which is valid to deduce the integrated near-field CD enhancements of chiral molecules in the presence of scatterers of any size and shape under general illumination conditions. Based on our analytical findings, we show that the near-field fCD factor can be related to magnitudes that can be computed in the far-field, i.e., the scattering cross-section and the helicity expectation value. Moreover, we show that in the case of lossless cylindrically symmetric samples, the near-field fCD factor can be inferred experimentally only from two far-field measurements at specific scattering angles. Our contribution paves the way for the experimental characterization of devices capable of enhancing molecular CD spectroscopy.

physics.optics↗