arXiv subjects

Cefe López

Publications and source records attributed to Cefe López.

10 recordsLinked to original sources

arXiv2026

Robust Radiative Cooling in Functionalizable Silica Microsphere Paints

Disordered coatings based on silica microspheres provide a scalable and robust platform for passive daytime radiative cooling. While particle-size optimization is often considered critical for enhancing solar scattering, the role of microsphere diameter once a coating operates in the multiple-scattering regime remains unclear. Here, we characterize the radiative cooling performance of disordered, optically thick photonic glass coatings with diameters ranging from 2 to 8 um. Despite measurable differences in microscopic scattering properties, both the spectral radiative response and the net cooling performance are robust to variations in particle diameter when the system operates deep in the diffusive regime. Outdoor thermal measurements reveal nearly identical steady-state temperature reductions across the full size range. These results indicate that radiative cooling in photonic glass coatings is governed by collective light transport, enabling microsphere size to be selected based on surface chemistry or processing constraints without compromising cooling performance.

physics.optics↗

arXiv2026

Universality and anisotropy of the Photonic Urbach Tail

Disorder in photonic crystals and waveguides creates states inside the photonic band gap. These states are often described as Lifshitz tails despite exhibiting energy distributions inconsistent with Lifshitz statistics near the band edge. Here we show that in photonic-crystal waveguides with intentionally engineered anisotropic disorder, the band-edge tail accessible experimentally follows an Urbach law universally, with cumulative statistics $F(Δ)=\exp[-(Δ/α)^β]$, where $Δ$ is the spectral detuning from the band edge, and an exponent $β\approx 1$ independent of disorder strength and orientation. In contrast to Lifshitz behavior, the density of states is maximal at the band edge and decays into the gap. Crucially, we find that the Urbach energy $α$ is anisotropic, with a pronounced directional splitting and qualitatively different scaling for disorder parallel and perpendicular to the waveguide axis. These conclusions are supported by quantitative agreement between optical measurements of GaAs photonic-crystal waveguides and full-vector simulations. The anisotropic Urbach energy emerges as a sensitive probe of disorder-mode coupling and a practical metric to characterize structural disorder in photonic devices.

physics.optics↗

arXiv2025

Wavelength-commensurate anatase TiO\_2 particles for ro-bust and functional Mie resonances across the visible and near infrared

Earth-abundant materials exhibiting Mie resonances across the visible and near-infrared offer opportunities for efficient and sustainable sensing, thermal regulation, and sunlight harvesting. For anatase TiO$_2$, a broadband optical and abundant material, Mie calculations indicate that robust resonances require size tunability and monodispersity (standard deviation, $\lesssim$ 5\%) over an extended range (0.5-2 $μ$m) not yet experimentally covered, while maintaining a refractive index above 2 to ensure optical contrast, for example with biomolecules. Here, we demonstrate that a simple UV-assisted thermal hydrolysis route yields anatase particles that meet all these criteria and remain aqueous-processable. Consequently, the materials display intense and modulable Mie resonances across the visible/near-infrared regions (including biological windows), outperforming previous results that were limited by size. Strong optical resonances combined with ambient-temperature processability enable robust, broadband, label-free detection of transparent biomolecules. Our insights advance precise synthesis and Mie-based photonics of an earth-abundant material, and indicate the potential for cost-effective and rapid-on-demand integration via printing technologies, further enhanced by anatase's biocompatibility and photochemical properties.

cond-mat.mtrl-sci↗

arXiv2025

Rough Fabry-Perot cavity: a vastly multi-scale numerical problem

A commercial Fabry-Perot laser diode is characterized by highly disproportionate dimensions, which poses a significant numerical challenge, even for state-of-the-art tools. This challenge is exacerbated when one of the cavity mirrors is rough-ened, as is the case when fabricating random laser diodes. Such a system involves length scales from several hundred mi-crometres (length) to a few nanometres (roughness) all of which are relevant when studying optical properties in the visi-ble. While involving an extreme range of dimensions, these cavities cannot be treated through statistical approaches such as those used with self-similar fractal structures known to show well-studied properties. Here we deploy numerical meth-ods to compute cavity modes and show how random corrugations of the Fabry-Perot cavity wall affect statistical proper-ties of their spectral features. Our study constitutes a necessary first step in developing technologically essential devices for photonic computation and efficient speckle-free illumination.

physics.optics↗

arXiv2022

Artificial Intelligence and Advanced Materials

Artificial intelligence is gaining strength and materials science can both contribute to and profit from it. In a simultaneous progress race, new materials, systems and processes can be devised and optimized thanks to machine learning techniques and such progress can be turned into in-novative computing platforms. Future materials scientists will profit from understanding how machine learning can boost the conception of advanced materials. This review covers aspects of computation from the fundamentals to directions taken and repercussions produced by compu-tation to account for the origins, procedures and applications of artificial intelligence. Machine learning and its methods are reviewed to provide basic knowledge on its implementation and its potential. The materials and systems used to implement artificial intelligence with electric charges are finding serious competition from other information carrying and processing agents. The impact these techniques are having on the inception of new advanced materials is so deep that a new paradigm is developing where implicit knowledge is being mined to conceive materi-als and systems for functions instead of finding applications to found materials. How far this trend can be carried is hard to fathom as exemplified by the power to discover unheard of mate-rials or physical laws buried in data.

cond-mat.mtrl-sci↗

arXiv2021

Electrically driven random lasing from a modified Fabry-Perot laser diode

Random lasers (RLs) are intriguing devices with promising applications as light sources for imaging, sensing, super resolution spectral analysis or complex networks engineering. RLs can be obtained from optically pumped dyes, optical fibers and crystals, or electrically pumped semiconductor heterostructures. Semicon-ductor RLs are usually fabricated by introducing scattering defects into the active layer, adding a degree of complexity to the fabrication process and losing the ease of realization potentially offered by disordered structures. Ready availability of electrically pumped RLs, avoiding costly fabrication approach, would boost the use of these devices in research and applications. Here, we realize an incoherent semiconductor RL by simply processing the output mirror of an off-the-shelf Fabry-Perot laser diode via controlled laser ablation. Optical feedback provided by the intact back mirror and the ablated front mirror results in multi-mode ran-dom lasing with low spatial coherence and speckled output emission profile.

physics.optics↗

arXiv2020

End-coupled random lasers: a basis for artificial neural networks

Light interference in strongly disordered photonic media can generate lasers where random modes are amplified in unpredictable way. The ease of fabrication, along with their low coherence caused by multiple small-linewidth peaks, made random lasers (RL) emerging, efficient, speckle-free light sources and a means to achieve spectral super-resolution. With potential to become a mature and accessible technology, their complex system's nature furnishes endless opportunities to unveil fundamental physics, since they can act as elements of optical network architectures. To date no experimental studies have analyzed the optical interaction between independent resonators in networks of RLs. Realizing RLs with a pumped strip joining two rough mirrors, we experimentally investigate and numerically simulate the emergence of networks when, by sharing scattering centers, RLs become coupled. We prove that the emission of a single RL can be manipulated by the action of others in the network, giving rise to substantial peak rearrangements and energy redistribution, fingerprint of mode coupling. Our findings, involving a few coupled RLs, firmly set the basis for the study of full-grown photonic networks. Oddly, both their deep understanding and their deployment as hardware clearly point in the direction of a novel disruptive technology: artificial intelligence on photonic random neural networks.

physics.optics↗

arXiv2016

Percolation in photonic crystals revealed by Fano Resonance

The understanding of how the arrangement of defects in photonic crystals impacts its photonic properties is cru-cial for the design of functional materials based thereon. By preparing photonic crystals with random missing scatterers we create crystals where disorder is embodied as vacancies in an otherwise perfect lattice rather than the usual positional or size disorder. We show that the amount of defects not only determines the intensity but also the nature of the light scattering. As the amount of defects varies, light scattering undergoes a transition whereby the usual signatures of photonic gaps (Bragg peak) suffer line-shape changes (Bragg dip) that can be readily described with the Fano resonance q parameter. When the amount of vacancies reaches the percolation threshold, q undergoes a sign change signaling the transition from a crystal to a mosaic of microcrystals through a state where scattering is maximum. Beyond that point the system reenters a state of low scattering that ap-pears in the guise of normal Bragg diffraction.

physics.optics↗

arXiv2011

Measurement of transport mean free path of light in thin systems

We extensively investigate in-plane light diffusion in systems with thickness larger than but comparable with the transport mean free path. By exploiting amplified spontaneous emission from dye molecules placed in the same holder of the sample, we obtain a directional probe beam precisely aligned to the sample plane. By comparing spatial intensity distribution of laterally leaking photons with predictions from random walk simulations, we extract accurate values of transport mean free path, opening the way to the investigation of a previously inaccessible kind of samples.

physics.optics↗

arXiv2010

Optical amplification enhancement in photonic crystals

Improving and controlling the efficiency of a gain medium is one of the most challenging problems of laser research. By measuring the gain length in an opal based photonic crystal doped with laser dye, we demonstrate that optical amplification is more than twenty-fold enhanced along the Gamma-K symmetry directions of the face centered cubic photonic crystal. These results are theoretically explained by directional variations of the density of states, providing a quantitative connection between density of the states and light amplification.

physics.optics↗