Direct Light Research Articles

A Diffusion Approach to Radiance Field Relighting using Multi‐Illumination Synthesis

AbstractRelighting radiance fields is severely underconstrained for multi‐view data, which is most often captured under a single illumination condition; It is especially hard for full scenes containing multiple objects. We introduce a method to create relightable radiance fields using such single‐illumination data by exploiting priors extracted from 2D image diffusion models. We first fine‐tune a 2D diffusion model on a multi‐illumination dataset conditioned by light direction, allowing us to augment a single‐illumination capture into a realistic – but possibly inconsistent – multi‐illumination dataset from directly defined light directions. We use this augmented data to create a relightable radiance field represented by 3D Gaussian splats. To allow direct control of light direction for low‐frequency lighting, we represent appearance with a multi‐layer perceptron parameterized on light direction. To enforce multi‐view consistency and overcome inaccuracies we optimize a per‐image auxiliary feature vector. We show results on synthetic and real multi‐view data under single illumination, demonstrating that our method successfully exploits 2D diffusion model priors to allow realistic 3D relighting for complete scenes.

High-efficiency thermo-optic control of a longitudinal radiation angle in a silicon-based optical phased array by leveraging the backside air trench structure.

We proposed a 2D 1 × 64 silicon optical phased array with a backside silicon-etched structure to achieve high tuning efficiency and a wide longitudinal steering range. At the radiator array, the n-i-n heater was implemented to steer the light in a longitudinal direction through the thermo-optic effect. The deep reactive ion etching process was utilized to generate the 600 µm depth air trench with a 1.8 cm2 area from the backside of the radiator array. We achieved almost 100% increment in terms of tuning efficiency, which is 1.56°/W for the proposed structure and 0.78°/W for the conventional structure.

Neural Histogram‐Based Glint Rendering of Surfaces With Spatially Varying Roughness

AbstractThe complex, glinty appearance of detailed normal‐mapped surfaces at different scales requires expensive per‐pixel Normal Distribution Function computations. Moreover, large light sources further compound this integration and increase the noise in the Monte Carlo renderer. Specialized rendering techniques that explicitly express the underlying normal distribution have been developed to improve performance for glinty surfaces controlled by a fixed material roughness. We present a new method that supports spatially varying roughness based on a neural histogram that computes per‐pixel NDFs with arbitrary positions and sizes. Our representation is both memory and compute efficient. Additionally, we fully integrate direct illumination for all light directions in constant time. Our approach decouples roughness and normal distribution, allowing the live editing of the spatially varying roughness of complex normal‐mapped objects. We demonstrate that our approach improves on previous work by achieving smaller footprints while offering GPU‐friendly computation and compact representation.

Establishment and Solution of a Finite Element Gas Exchange Model in Greenhouse-Grown Tomatoes for Two-Dimensional Porous Media with Light Quantity and Light Direction

An accurate gas utilization model is essential for precisely detecting plant photosynthetic capacity. Existing equipment for measuring the plant photosynthetic rate typically considers the key parameters of mesophyll cell conductance and a photosynthetic model based on the carbon reaction process under direct light conditions. However, the light environment signals received by the plant canopy not only vary significantly in incidence angles, but the effective light intensity also differs greatly from the measured values under vertical incidence conditions. To reduce the deviation between existing photosynthetic models and the actual photosynthetic efficiency of leaves, this study employs the gas diffusion method from engineering, using the finite element approach. Based on elastic mechanics and seepage mechanics, the internal stress field control equation of tomato leaves and the two-phase flow equation under a CO2 porous medium were derived. A mathematical model of porous gas–liquid two-phase fluid-solid coupling was established, solved, and analyzed. Preliminary verification was conducted through tests. The results show that in the initial stage of CO2 entering the leaf, the gas flow velocity is higher because of the larger pressure gradient between the pore and the leaf. In this stage, the gas diffusion rate is higher. As the intake time increases, the pressure gradient gradually decreases, and the inlet velocity slows down. Consequently, the diffusion rate gradually reduces. Because of the coupling of light quantity and light direction, the gas diffusion rate significantly increases compared with the uncoupled model. Additionally, a diffusion model that does not consider fluid–solid coupling will overestimate the gas flow rate as the depth of gas entry increases. Therefore, the internal gas diffusion model must account for the effect of coupling on the diffusion rate.

Realization of nonreciprocal photon statistics by manipulating the quantum nonlinearity of cold atoms in an asymmetric cavity

In a strongly coupled cavity quantum electrodynamics (QED) system, the second-order correlation function g(2)(τ) of the transmitted probe light from the cavity is determined by the nonlinearity of the atom in the cavity. Therefore, the system provides a platform for controlling the photon statistics by manipulating nonlinearity. In this paper, we experimentally demonstrate nonreciprocal quantum statistics in a cavity QED system with several atoms strongly coupled to an asymmetric optical cavity, which is composed of two mirrors with different transmittivities. When the direction of the probe light is reversed, the intracavity light field alternates to a different level. Distinct photon statistics are then observed due to the quantum nonlinearity associated with strongly coupled atoms. Sub-Poissonian photon-number statistics for forward light and a Poissonian distribution for backward light are then realized. Our work provides an effective approach for realizing nonreciprocal quantum devices, which have potential applications in the unidirectional generation of nonclassical light fields and quantum sensing.

Protective properties of spectacle lenses used as ultraviolet blockers

In this study, we evaluated the UV transmittance of spectacle lenses in the Turkish market, which are reported to have UV blocking properties, and tested their suitability. Samples were obtained from patients who were admitted to the ophthalmology outpatient clinic of our hospital for refractive error and who wore glasses as UV block. No limitation was made regarding the spectacle size and duration of spectacle wear. Measurements were tested by the principal investigator using an ultraviolet detector. The right and left lens were measured separately. All measurements were performed at room temperature (22-25°C) in a humidity regulated (20-40%) room without direct light. UV protection level was measured for 120 spectacles used for refractive errors. Only 28 (23.3%) of 120 glasses had protection level up to 400 nm UV. Twenty-four (20%) of the glasses had a protection level of 0 even though they were labeled as having UV blocking properties. It is clear that strict regulations need to be implemented to improve the protection levels of glasses.

Geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 from first-principles calculation

In this paper, the geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 have been systematically studied by first-principles calculation. The results show that Na3AgO2 is mechanically stable and has small compressibility. Na3AgO2 is an indirect band-gap semiconductor with weak interatomic interaction. The bandgap calculated by HSE06 is 2.314 eV, and that calculated by GGA is 1.261 eV. For Na3AgO2, in the valence band near the Fermi level, the curve peaks of TDOS at −2.11 eV and −0.885 eV are primarily composed of O 2p states, which hybridize the 4 d and 4p states of Ag. The conduction band mainly consists of the 4p, 4 d, and 5s states of Ag, while hybridizing a few 2p states of O and a few 2p and 3s states of Na. As can be seen from the phonon dispersion spectrum there is no negative phonon frequency in the whole Brillouin region, indicating the structure is stable. Mulliken bond population of Na3AgO2 shows that O–Ag bonds have strong covalency, O–Na bonds have strong ionic properties, Na–Na bonds and Na–Ag bonds are antibonding. Na3AgO2 has a small reflectivity and a small absorption coefficient in the direction of (100) and (010) and has good transparency. The transparency of blue-violet light in the (001) direction is not as good as that of low-energy visible light. The obtained results lead to the conclusion that Na3AgO2 is a promising p-type transparent conducting material and is expected to be applied in practice.

Optical switching with high-Q Fano resonance of all-dielectric metasurface governed by bound states in the continuum

The discovery of bound states in the continuum (BIC) of optical nanostructures has garnered significant research interest and found widespread application in the field of optics, leading to an attractive approach to achieve high-Q (Quality factor) Fano resonance. Herein, an all-dielectric metasurface consisting of four gallium phosphide (Gap) cylinders on the MgF2 substrate is designed and analyzed by the finite element method (FEM). By breaking the symmetry of the plane, specifically by moving the two cylinders to one side, it is possible to achieve a transition from the symmetry-protected BIC to quasi-BIC. This transition enables the excitation of sharp dual-band Fano resonance at wavelengths of 1,045.4 nm and 1,139.6 nm, with the maximum Q factors reaching 1.47 × 104 and 1.28 × 104, respectively. The multipole decomposition and near-field distributions show that these two QBICs are dominated by the electric quadrupole (EQ) and magnetic quadrupole (MQ). Furthermore, bidirectional optical switching can be accomplished by changing the polarization direction of the incident light. As a result, the maximum sensitivity and figure of merit (FOM) are 488.9 nm/RIU and 2.51 × 105 RIU-1, respectively. The results enrich our knowledge about BIC and reveal a platform for the development of high-performance photonics devices such as optical switches and sensors.

A Fully-correlated Anisotropic Micrograin BSDF Model

We introduce an improved version of the micrograin BSDF model [Lucas et al. 2023] for the rendering of anisotropic porous layers. Our approach leverages the properties of micrograins to take into account the correlation between their height and normal, as well as the correlation between the light and view directions. This allows us to derive an exact analytical expression for the Geometrical Attenuation Factor (GAF), summarizing shadowing and masking inside the porous layer. This fully-correlated GAF is then used to define appropriate mixing weights to blend the BSDFs of the porous and base layers. Furthermore, by generalizing the micrograins shape to anisotropy, combined with their fully-correlated GAF, our improved BSDF model produces effects specific to porous layers such as retro-reflection visible on dust layers at grazing angles or height and color correlation that can be found on rusty materials. Finally, we demonstrate very close matches between our BSDF model and light transport simulations realized with explicit instances of micrograins, thus validating our model.

Half-wave voltage controllable optical voltage sensor with arbitrary electric field direction modulation*

Abstract An optical voltage sensor with an arbitrary electric field direction modulation (AEFDM) mode is proposed to increase the half-wave voltage. The mode is realized by heterogeneous electrodes arranged in a center-symmetric way, and generates an electric field with a direction at an arbitrary angle to the light propagation direction. The finite element method and coupling wave theory are used to design and optimize the electrodes and field distribution. The experimental results show that heterogeneous electrodes and AEFDM mode are able to regulate the sensor’s half-wave voltage in a range from 1 to 30 times (47–1409 kV), with 0.5 class accuracy and 99.99% linearity. This novel AEFDM method proposes a new electrode shape and position, reducing temperature drift to 50% compared to solid-state voltage divider method.

Organic Semiconductor-BiVO4 Tandem Devices for Solar-Driven H2O and CO2 Splitting.

Photoelectrochemical (PEC) devices offer a promising platform toward direct solar light harvesting and chemical storage through artificial photosynthesis. However, most prototypes employ wide bandgap semiconductors, moisture-sensitive inorganic light absorbers, or corrosive electrolytes. Here, the design and assembly of PEC devices based on an organic donor-acceptor bulk heterojunction (BHJ) using a carbon-based encapsulant are introduced, which demonstrate long-term H2 evolution and CO2 reduction in benign aqueous media. Accordingly, PCE10:EH-IDTBR photocathodes display long-term H2 production for 300 h in a near-neutral pH solution, whereas photocathodes with a molecular CO2 reduction catalyst attain a CO:H2 selectivity of 5.41±0.53 under 0.1 sun irradiation. Their early onset potential enables the construction of tandem PCE10:EH-IDTBR - BiVO4 artificial leaves, which couple unassisted syngas production with O2 evolution in a reactor completely powered by sunlight, sustaining a 1:1 ratio of CO to H2 over 96 h of operation.

Exploration of Pilobolus sp. Fungi from Various Livestock Manures in Kedung Pacul Village, Klaten

Pilobolus is a coprophilous fungus belonging to the Zygomycota. Pilobolus sp. is called a coprophilous fungus because it can live in animal feces. The uniqueness of this fungus is that it can shoot its spores, so Pilobolus sp. is called a shotgun fungus. Pilobolus sp. exhibits a phototropism mechanism in which the sporangium shoots spores in the direction of light. Pilobolus has a unique living habitat, namely in the manure of herbivores such as cows, goats, sheep, etc. This habit of life may seem terrible to us, but fungi like Pilobolus sp. are very important in life because they are a type of decomposer, capable of breaking down organic matter from dead living things. So the purpose of this study was to observe the spores produced by the fungus Pilobolus sp. (a fungus in animal waste). The method used was to cultivate the fungus Pilobolus sp. for seven days on various animal wastes placed in jam bottles. The results showed that the Pilobolus sp. fungus grew on various media of animal feces, such as horses, cows, goats, and pigs, with different growth times, and there were also spores shot on the glass walls that had been perforated.

Linearly polarized GaN micro-LED with adjustable directional emission integrated with a continuous metasurface

Traditional LEDs emit light that exhibits incoherence and displays a Lambertian distribution. To achieve linearly polarized (LP) light and control the emission direction, a variety of optical components are required to be stacked, which is unsuitable for compact applications and results in low deflection efficiency. Here, we propose and and numerically simulate a novel single-chip micro-resonant cavity LED (micro-RCLED) device that generates directional LP light by integrating a continuous metasurface. This device includes a bilayer grating at the GaN layer's bottom, providing high transverse electric (TE) reflectivity above 89.5% and an extinction ratio exceeds 57 dB at 500 nm. The top distributed Bragg reflector (DBR) and the bilayer grating together constitute a TE mode Fabry–Pérot resonant cavity. This not only promotes the emission of the TE wave, but also guarantees its collimation with the appropriate phase, thereby enhancing its spatial coherence. A functional metasurface above the DBR layer precisely controls the TE wave's deflection angle. It maintains a low aspect ratio while enabling efficient, large-angle deflection. The simulation results demonstrate that this device provides an effective solution for generating highly spatially coherent directional LP light, with broad potential applications in fields such as polarized light imaging and advanced 3D micro-LED display systems.

Enhancing photoluminescence of WSe2 in vapor grown WSe2/VOCl bilayer heterojunctions via surface passivation.

Monolayer tungsten selenide (WSe2) has attracted attention due to its direct bandgap-generated strong light emission and light-matter interaction. Herein, vertical WSe2/VOCl bilayer heterojunctions with enhanced PL of WSe2 were synthesized by the vapor growth method. The morphology, crystal structure, and chemical composition of the WSe2/VOCl heterojunctions were systematically investigated, which confirmed the successful formation of the heterojunctions. The PL emission intensity of WSe2 obtained from the WSe2/VOCl heterojunction was about 2.4 times higher than that of the WSe2 monolayer, demonstrating the high optical quality of the WSe2/VOCl heterojunction, which was further confirmed by time-resolved PL measurements. The insulator top VOCl, which was deposited on the surface of the semiconductor bottom WSe2 as a surface passivation material, reducing the impurities and resulting in an atomically clean surface, successfully enhanced the PL emission of the bottom WSe2. This vertical WSe2/VOCl bilayer heterojunction with PL enhancement could provide a promising platform for optical devices.

First-principles simulations of high-order harmonics generation in thin films of wide bandgap materials [Invited

High-order harmonics generation (HHG) is the only process that enables tabletop-sized sources of extreme ultraviolet (XUV) light. The HHG process typically involves light interactions with gases or plasma––material phases that hinder wider adoption of such sources. This motivates the research in HHG from nanostructured solids. Here, we employ the time-dependent density function theory (TDDFT) to investigate material platforms for HHG at the nanoscale using first-principles supercomputer simulations. We reveal that wide bandgap semiconductors, aluminum nitride (AlN) and silicon nitride (Si3N4), are highly promising for XUV light generation when compared to silicon, one of the most common nonlinear nanophotonic materials. In our calculations, we assume excitation with a 100 fs pulse duration, 1×1013W/cm2 peak power, and 800 nm central wavelength. We demonstrate that in AlN material the interplay between the crystal symmetry and the incident light direction and polarization can enable the generation of both even and odd harmonics. Our results should advance the development of high-harmonics generation of XUV light from nanostructured solids.

Light induced self-assembly of one-dimensional PT-symmetric optical system exhibiting pulling force

Light induced self-assembly’s non-contact and non-invasive nature, along with its versatility and dynamic assembly capabilities, make it particularly well-suited for the self-organization of particles. Previous self-assembly configurations are either in a static equilibrium state or in a dynamic equilibrium state driven by a pushing force. In this study, we introduce a one-dimensional parity-time symmetric (PT-symmetric) multilayer optical system consisting of balanced gain and loss, enabling the generation of a total pulling force on the structure. By conducting molecular dynamics simulations, we achieve the self-organized structure exhibiting pulling force. Furthermore, by reversing the direction of the incident light, we realized pushing force induced binding. The stability of the bound structure is also analyzed using linear stability analysis. Additionally, the light induced self-assembly exhibiting pulling and pushing force is achieved in the one-dimensional multilayer system with unbalanced gain and loss. This work provides an additional degree of freedom in the self-organization of particles.

Concrete crack pixel-level segmentation: a comparison of scene illumination angle of incidence

Previous research has demonstrated how angled and directional lighting can enhance the detection of concrete cracks in low-light environments and outperform diffused lighting alternatives. This paper investigates the effect of different angles of incidence of directional lighting for concrete crack pixel-level segmentation. Five directional lighting datasets of cracked concrete slabs were captured, each using an angle of incidence of 10, 20, 30, 40, and 50 degrees, respectively. A directional lighting crack segmentation algorithm was applied to each lighting angle dataset. Algorithm output comparisons with ground truths revealed that the directional lighting method performed best on the 50-degree lighting dataset, obtaining a recall, precision, and F1 score of 68%, 81%, and 74%, respectively. However, qualitative analysis of the segmentation outputs on a sub-image scale revealed that towards the edges of the images, the segmentation performance of 30-degree lighting was significantly better, with results closely matching those of the ground truth. This research highlights that the lighting angle of incidence can increase the performance of directional lighting concrete crack segmentation depending on defect position. The results from this work have the potential to improve low-light environment concrete crack detection and monitoring.

Peroxymonosulphate activation by ultra-small Ni@NiFe2O4/ZnO magnetic nanocomposites for solar photocatalytic degradation of β-lactam antibiotic - cefadroxil

In this study, ultra-small nickel nanoparticles on NiFe2O4 (Ni@NiFe2O4) and Ni@NiFe2O4/ZnO magnetic nanocomposites were synthesized and utilized for the solar light-driven photocatalytic degradation of cefadroxil. The drug cefadroxil is widely used to treat bacterial infections and cefadroxil is a non-biodegradable pharmaceutical compound detected in the groundwater sources because of its low removal efficiency. The Raman active phonon at 540 cm−1 confirms the presence of Ni nanoparticles at the surface of NiFe2O4/ZnO. DR-UV-Vis analysis exhibited surface plasmon resonance at 350 nm for ultra-small nickel nanoparticles. The observed optical bandgap values for Ni@NiFe2O4 and NiFe2O4/ZnO are 1.2 eV and 2.43 eV, respectively. Which indicates that these magnetic nanocomposites can be utilized for the mineralization of cefadroxil (β-lactam antibiotic) under ambient environmental conditions. The efficiency was determined by the direct solar light driven photocatalytic oxidation of cefadroxil in the presence and absence of peroxymonosulphate (PMS). The experimental findings exhibits that ∼95 % of cefadroxil (CDL) was eliminated by the ultra-small Ni@NiFe2O4/ZnO within 60 min (k = 7.5 × 10−4 s−1) of direct solar light irradiation. Further, the addition of PMS enhanced the photodegradation to achieve 100 % cefadroxil oxidation within 40 min (k = 25 × 10−4 s−1) of direct sunlight. The efficiency of the nanocatalyst was compared with controlled experiments and was found to be Fe2O3 < ZnO < TiO2 (P25) < Ni@NiFe2O4 < Ni@NiFe2O4/ZnO under absence and presence of PMS. Moreover, ultra-small Ni@NiFe2O4/ZnO nanophotocatalyst were stable up to 3 consecutive cycles.

Reinforcing the photocatalytic removal of ibuprofen antibiotic over S-scheme 2D/1D Bi12O17Cl2/V2O5 heterojunction under solar light illumination

In our work, the Bi12O17Cl2/V2O5 hybrid with a favorable S-scheme mechanism was prepared via a simple self-assembly procedure for ibuprofen (IBF) oxidation under solar light energy. The 2D Bi12O17Cl2 provides abundant active sites to immobilize 1D V2O5 nanorods, enhancing the interaction between two semiconductors. The establishment of the 2D/1D structure reflected a positive effect on the surface area of Bi12O17Cl2/V2O5-10 %, which was linked to the reduction in the aggregation rate of V2O5 nanorods. Amazingly, optimal Bi12O17Cl2/V2O5 photocatalysts achieved exceptional IBF degradation capacities of 88.6 % and 71.3 % under LED and direct solar light irradiation, respectively. Among the samples, the optimized Bi12O17Cl2/V2O5-10 % reflected the best IBF oxidation kinetic with a reaction constant of 0.03894 min− 1, which is stronger than pristine Bi12O17Cl2 (0.00885 min− 1) and V2O5 (0.0119 min− 1) by 4.4 and 3.27 times, respectively. The promoted catalytic activity was correlated to the S-scheme heterojunction between Bi12O17Cl2 and V2O5 that could upgrade the solar light absorbance, facilitate the separation and transportation of charge carriers, and strengthen the redox potential of Bi12O17Cl2/V2O5. Furthermore, the parameters revealed the best IBF treatment at a catalyst dosage of 0.6 g/L and a pH value of 7. Besides, Bi12O17Cl2/V2O5-10 % recorded outstanding catalytic stability in six cycles without notable alteration in its structure, morphology, or optical properties. On the other hand, the radical quenching tests declared that •O2− and •OH play major contributions in IBF photooxidation over Bi12O17Cl2/V2O5-10 %. Finally, our work offers vital guidance towards designing robust bismuth-based heterojunctions for efficient degradation of IBF antibiotics in a sustainable and cost-effective strategy.

Goos–Hänchen shifts on spin representation

We analyze the Goos–Hänchen (GH) shift and longitudinal spin splitting (LSS) at a planar interface between two optical media in the spin representation. While these optical effects have been studied previously, we examine the direct and cross-reflected light fields, and their interference from the spin representation to reveal the physical mechanism of the GH shift and establish a quantitative relationship between it and LSS. Furthermore, we show that angular asymmetric spin splitting occurs under the spin representation when linearly polarized light with a phase difference of 180° and an amplitude ratio angle deviating from 45° impinges on the air–glass interface at Brewster’s angle. Finally, we reveal that the spin component field of the reflected light field for the total reflection case is different from that of the Brewster angle reflection, the most typical manifestation is that the intensity of the two spin component fields is not equal.