Light Phenomena Research Articles

Superscattering of light: fundamentals and applications.

Superscattering, theoretically predicted in 2010 and experimentally observed in 2019, is an exotic scattering phenomenon of light from subwavelength nanostructures. In principle, superscattering allows for an arbitrarily large total scattering cross section, due to the degenerate resonance of eigenmodes or channels. Consequently, the total scattering cross section of a superscatterer can be significantly enhanced, far exceeding the so-called single-channel limit. Superscattering offers a unique avenue for enhancing light-matter interactions and can enable numerous practical applications, ranging from sensing, light trapping, bioimaging, and communications to optoelectronics. This paper provides a comprehensive review of the recent progress and developments in the superscattering of light, with a specific focus on elucidating its theoretical origins, experimental observations, and manipulations. Moreover, we offer an outlook on future research directions in superscattering, including potential realizations of directional superscattering, scattering-free plasmonic superscattering, enhancement of free-electron radiation and the Purcell effect via superscatterers, inelastic superscattering, and superscattering of non-electromagnetic waves.

Precomputed low-frequency lighting in cinematic volume rendering.

Cinematic Rendering (CR) employs physical models such as ray tracing and global illumination to simulate real-world light phenomena, producing high-quality images with rich details. In the medical field, CR can significantly aid doctors in accurate diagnosis and preoperative planning. However, doctors require efficient real-time rendering when using CR, which presents a challenge due to the substantial computing resources demanded by CR's ray tracing and global illumination models. Precomputed lighting can enhance the efficiency of real-time rendering by freezing certain scene variables. Typically, precomputed methods freeze geometry and materials. However, since the physical rendering of medical images relies on volume data rendering of transfer functions, the CR algorithm cannot utilize precomputed methods directly. To improve the rendering efficiency of the CR algorithm, we propose a precomputed low-frequency lighting method. By simulating the lighting pattern of shadowless surgical lamps, we adopt a spherical distribution of multiple light sources, with each source capable of illuminating the entire volume of data. Under the influence of these large-area multi-light sources, the precomputed lighting adheres to physical principles, resulting in shadow-free and uniformly distributed illumination. We integrated this precomputed method into the ray-casting algorithm, creating an accelerated CR algorithm that achieves more than twice the rendering efficiency of traditional CR rendering.

Paper Crystallisations

Abstract This essay investigates the graphical and diagrammatic techniques the Dutch mathematician and natural philosopher Christiaan Huygens (1629–1695) employs in his meteorological investigations. A distinction is discerned between Huygens’ drawings of crystalline structures under the microscope, and his hypothetical modelling of different types of atmospheric light-refracting bodies. It is demonstrated, however, that both domains of inquiry are intricately connected through Huygens’ longstanding interest in “wondrous” light refraction phenomena in the atmosphere, such as solar halos and parhelia.

Controlling directional emission of ions attached on the surface of nanoparticles

Abstract The interaction between lasers and nanoparticles holds significant theoretical and practical importance. Here, we investigate the near-field enhancement effects on silver nanotriangles and nanodiscs under ultrafast laser pulses, as well as the dynamics of protons and ions attached to the nanoparticle surfaces. By adjusting the size parameters of the nanoparticles, we explore the near-field enhancement effects and proton emission dynamics at different laser wavelengths. The results demonstrate that nanoparticles with varying morphologies substantially impact the proton momentum spectrum. The directional proton emission of nanotriangle structures is more pronounced compared to that of nanodiscs, and this effect can be further enhanced by adjusting the laser wavelength. Additionally, manipulating the thickness of particles also controls the Mie scattering phenomenon of light. Finally, we qualitatively discuss the emission processes of alpha particles and 9C6+ heavy ions. This research has important implications for proton and heavy ion radiotherapy in cancer treatment and targeted drug delivery, while providing theoretical foundations for understanding, characterizing, and controlling experimental studies of nanosystems with significant potential for expanding research into microdynamic behavior in complex nanomaterial superstructures.

A novel application of laser speckle imaging technique for prediction of hypoxic stress of apples

BackgroundFruit storage methods such as dynamic controlled atmosphere (DCA) technology enable adjusting the level of oxygen in the storage room, according to the physiological state of the product to slow down the ripening process. However, the successful application of DCA requires precise and reliable sensors of the oxidative stress of the fruit. In this study, respiration rate and chlorophyll fluorescence (CF) signals were evaluated after introducing a novel predictors of apples' hypoxic stress based on laser speckle imaging technique (LSI).ResultsBoth chlorophyll fluorescence and LSI signals were equally good for stress detection in principle. However, in an application with automatic detection based on machine learning models, the LSI signal proved to be superior, due to its stability and measurement repeatability. Moreover, the shortcomings of the CF signal appear to be its inability to indicate oxygen stress in tissues with low chlorophyll content but this does not apply to LSI. A comparison of different LSI signal processing methods showed that method based on the dynamics of changes in image content was better indicators of stress than methods based on measurements of changes in pixel brightness (inertia moment or laser speckle contrast analysis). Data obtained using the near-infrared laser provided better prediction capabilities, compared to the laser with red light.ConclusionsThe study showed that the signal from the scattered laser light phenomenon is a good predictor for the oxidative stress of apples. Results showed that effective prediction using LSI was possible and did not require additional signals. The proposed method has great potential as an alternative indicator of fruit oxidative stress, which can be applied in modern storage systems with a dynamically controlled atmosphere.

Materiality & light: case studies exploring architectural surfaces informed by light behavior

This paper outlines three case studies that explore the relationship between form, material behavior, and light performance. Each case study appropriates methods of computational analysis, parametric design, and digital fabrication to construct directed light fields and patterns from architectural surfaces in public spaces. Each project explores how controlled conditions of materiality and light phenomena may provide opportunities to reengage the physicality of human experience by generating effects that attempt to enhance human interaction and spatial perception.

Occlusion-aware deep convolutional neural network via homogeneous Tanh-transforms for face parsing

Face parsing infers a pixel-wise label map for each semantic facial component. Previous methods generally work well for uncovered faces, however, they overlook facial occlusion and ignore some contextual areas outside a single face, especially when facial occlusion has become a common situation during the COVID-19 epidemic. Inspired by the lighting phenomena in everyday life, where illumination from four distinct lamps provides a more uniform distribution than a single central light source, we propose a novel homogeneous tanh-transform for image preprocessing, which is made up of four tanh-transforms. These transforms fuse the central vision and the peripheral vision together. Our proposed method addresses the dilemma of face parsing under occlusion and compresses more information from the surrounding context. Based on homogeneous tanh-transforms, we propose an occlusion-aware convolutional neural network for occluded face parsing. It combines information in both Tanh-polar space and Tanh-Cartesian space, capable of enhancing receptive fields. Furthermore, we introduce an occlusion-aware loss to focus on the boundaries of occluded regions. The network is simple, flexible, and can be trained end-to-end. To facilitate future research of occluded face parsing, we also contribute a new cleaned face parsing dataset. This dataset is manually purified from several academic or industrial datasets, including CelebAMask-HQ, Short-video Face Parsing, and the Helen dataset, and will be made public. Experiments demonstrate that our method surpasses state-of-the-art methods in face parsing under occlusion.

Understanding the Photoprocesses in Biological Systems: Need for Accurate Multireference Treatment.

Light-matter interaction is crucial to life itself and revolves around many of the central processes in biology. The need for understanding these photochemical and photophysical processes cannot be overemphasized. Interaction of light with biological systems starts with the absorption of light and subsequent phenomena that occur in the excited states of the system. However, excited states are typically difficult to understand within the mean field approximation of quantum chemical methods. Therefore, suitable multireference methods and methodologies have been developed to understand these phenomena. In this Perspective, we will describe a few methods and methodologies suitable for these descriptions and discuss some persisting difficulties.

A Possible Aether Explanation for Two Light Phenomena: Varying Speed with Medium and Cosmological Redshift

The speed of light (3.00 x 105 km/s in a vacuum) lies beyond human comprehension, especially if one is to postulate that it can be achieved ballistically by a particle, even a “massless” one such as a photon. If such speeds are attainable, which experimentation and astronomical observation apparently have “proven,” then it is slightly less of a leap of faith to imagine such speeds to result from wave phenomena, suggesting that a propagating medium for light must exist (an “aether”) despite such allegedly having been disproven pre-Einstein. With this possibility in mind, two light phenomena are examined from the perspective of an aether as light’s medium of transmission.

P‐257: Late‐News Poster: Highly Efficient Geometrically Stretchable Organic Light Emitting Diodes with Angle Independent Narrow‐Band Emission

Herein, we demonstrated the first highly efficient geometrical stretchable top‐emitting organic light emitting diode by incorporating the pre‐stretched optical adhesive (OA) film. The enhancement of device efficiencies with light extraction phenomenon brought by the nanowavy corrugated structures of OA substrate. GSOLED shows stability in stretchable conditions and displays narrowband emission with color purity. The device shows very high current efficiency and EQE of 221 cd A ‐1 and 51 %.

Design and Development of a Non-invasive Opto-Electronic Sensor for Blood Glucose Monitoring Using a Visible Light Source.

Background The management of diabetes is critically dependent on the continuous monitoring of blood glucose levels. Contemporary approaches primarily utilize invasive methods, which often prove to be uncomfortable and can deter patient adherence. There is a pressing need for the development of novel strategies that improve patient compliance and simplify the process of glucose monitoring. Aim and objectives The primary objective of this research is to develop a non-invasive blood glucose monitoring system (NIBGMS) that offers a convenient alternative to conventional invasive methods. This study aims to demonstrate the feasibility and accuracy of using visible laser light at a wavelength of 650 nm for glucose monitoring and to address physiological and technical challenges associated with in vivo measurements. Methods Our approach involved the design of a device that exploits the quantitative relationship between glucose concentration and the refraction phenomena of laser light. The system was initially calibrated and tested using glucose solutions across a range of concentrations (25-500 mg/dL). To get around the problems that come up when people's skin and bodies are different, we combined an infrared (IR) transmitter (800 nm) and receiver that checks for changes in voltage, which are indicative of glucose levels. Results The prototype device was compared with a commercially available blood glucose monitor (Accu-Chek active machine; Roche Diabetes Care, Inc., Mumbai, India). The results demonstrated an average linearity of 95.7% relative to the Accu-Chek machine, indicating a high level of accuracy in the non-invasive measurement of glucose levels. Conclusions The findings suggest that our NIBGMS holds significant promise for clinical application. It reduces the discomfort associated with blood sampling and provides reliable measurements that are comparable to those of existing invasive methods. The successful development of this device paves the way for further commercial translation and could significantly improve the quality of life for individuals with diabetes, by facilitating easier and more frequent monitoring.

Tunable Fano resonance in a novel compact metal–insulator–metal structure

A novel compact scheme to realize tunable Fano resonance is proposed and investigated theoretically and numerically. The scheme is based on two slot cavities in a metal–insulator–metal structure. The model and formation mechanism of Fano resonance in this structure are studied. A new method based on four-mode temporal coupled-mode theory is used to analyze model of the structure with two slot cavities. Compared with previous studies, this method only considers the interaction between modes within two cavities rather than considering the energy coupling between them. The tunability and slow light phenomenon in the new structure are also studied. It is believed that research in this article can provide a new method to achieve Fano resonance. Furthermore, it is helpful to establish the Fano resonance model and reveal the formation mechanism of Fano resonance.

Beyond the Pump: A Narrative Study Exploring Heart Memory.

The field of organ transplantation, particularly heart transplantation, has brought to light interesting phenomena challenging traditional understandings of memory, identity, and consciousness. Studies indicate that heart transplant recipients may exhibit preferences, emotions, and memories resembling those of the donors, suggesting a form of memory storage within the transplanted organ. Mechanisms proposed for this memory transfer include cellular memory, epigenetic modifications, and energetic interactions. Moreover, the heart's intricate neural network, often referred to as the "heart brain," communicates bidirectionally with the brain and other organs, supporting the concept of heart-brain connection and its role in memory and personality. Additionally, observations from hemispherectomy procedures highlight the brain's remarkable plasticity and functional preservation beyond expectations, further underscoring the complex interplay between the brain, body, and identity. However, ethical and philosophical questions regarding the implications of these findings, including the definition of death and the nature of personal identity, remain unresolved. Further interdisciplinary research is needed to unravel the intricacies of memory transfer, neuroplasticity, and organ integration, offering insights into both organ transplantation and broader aspects of neuroscience and human identity. Understanding these complexities holds promise for enhancing patient care in organ transplantation and deepens our understanding of fundamental aspects of human experience and existence.

How Light Affects Circadian Rhythm and Mood Regulation

Light is full of the world and illuminates our lives, and scientists believe that light must play a crucial role in affecting humans either positively or negatively including circadian functions and emotion-related behaviors. Through experiments, researchers have revealed the fact that light can affect humans significantly and the principles behind phenomena of light influencing humans both physically and mentally. This essay focuses on how light works in humans’ circadian rhythm and mood regulation, and how exactly nocturnal light exposure induces depression-like behaviors. Many research results indicate that natural light can help reset circadian rhythm of humans when the normal circadian rhythm is disturbed by trans meridian travel or working during night. Thus, scientific time of light exposure helps to relieve jet-lag symptoms and allows people to have a healthier mental and physical state. Studies by Fernandez D C et al. and An K. et al. are included in this essay to demonstrate the effects of light on mood. Fernandez D C et al. experimentally confirm that PHb (perihabenular nucleus) is necessary in the circuit of light affecting mood through ipRGC which is the only receptor of light input to influence circadian functions of the brain. Subsequently, An K. et al. conducted a series of experiments on mice to investigate the role of a subcortical pathway regulated by circadian rhythms in modulating mood-related behaviors resulted from nighttime light exposure in mice. The findings provide insights into the mechanisms underlying the impact of nocturnal light on mood regulation and highlight the importance of considering circadian rhythms in understanding the effects of environmental factors on mental health. Overall, these studies allow more scientists to think about how to employ light as therapy as well as development of new anti-depressants based on the research of the ipRGC circuit.

Chirp-driven control over fast-slow light effects in epsilon-near-zero metamaterials.

Optical applications based on fast and slow light effects force the usage of metamaterials famous for their flexible dispersion properties. In this work, we apply the unique optical nonlocality of metal nanorod-based epsilon-near-zero (ENZ) metamaterials along with the chirp of femtosecond laser pulses for astonishing control of these effects. We demonstrate the switching between the fast and slow light phenomena via the change of the angle of incidence and/or the central wavelength of chirped pulses in the vicinity of metamaterial zero-transmission regime mediated by the ENZ nonlocality. We elucidate that the laser chirp allows one to manipulate and enhance the fast-slow light phenomena.

Low-cost optical home-lab experiments

Low-cost experiments have the advantage of being affordable to schools, universities, and families. In the particular case of optics, these experiments can be important to help students understand the properties of light and optical phenomena. In this article, we demonstrate optical experiments to be carried out at home by students learning remotely. These experiments were designed and performed at the 16th Summer School in Physics, which is a five-day activity for high school students organized by the University of Porto. This activity was organized remotely, with all lectures and activities being performed through video conferencing. The materials needed for the proposed experiments were sent by post to students before the beginning of school. The students were able to build optical experiments from scratch, perform measurements, analyse data and present their findings on the last day of the school in a public session dedicated to online presentations.

In-Depth Analysis on the Fabry-Perot Effect of Cs2AgBiBr6 Double Perovskite-Based Solar Cells via Optical Path Length Modulation

Herein, the Fabry-Perot (F-P) interference of cesium silver bismuth bromide (Cs2AgBiBr6) double perovskite solar cells has been analyzed by modulating the optical path length of each layer step by step using the finite-difference time-domain (FDTD) method. The study was performed pass through three main steps. In step 1, for the fluorine-doped tin oxide (FTO)/Cs2AgBiBr6 double perovskite/gold (Au) architecture, we increased the absorption layer thickness from 150 to 600 nm at intervals of 150 nm and then predicted the optical performance including the absorption and reflection. In step 2, titanium dioxide (TiO2) layer was added between FTO electrode and Cs2AgBiBr6 double perovskite and then scaled from 20 to 200 nm at intervals of 20 nm. In the analysis process, short-circuit current density (Jsc) repeatedly fell and rose as the TiO2 layer thickness increased, and when TiO2 layer thickness is 100 nm, Jsc showed the highest value of 13.91 mA/cm2. In step 3, by applying a spiro-OMeTAD layer between the Cs2AgBiBr6 double perovskite absorption layer and Au electrode, the Jsc showed a continuous increase with slight decrease as the spiro-OMeTAD layer thickness increased from 110 to 200 nm, and when the spiro-OMeTAD layer thickness was 200 nm, Jscwas calculated as 14.57 mA/cm2, which is the highest value in the range. In the case of the optimal condition of full structure device, the Fabry-Perot resonance peaks were discovered at 477, 520, 572, 659, and 778 nm five wavelength regions, and the influence of the Fabry-Perot resonance on the generation rate inside the absorption layer on the 520, 572, and 659 nm monochromatic wavelength light was analyzed according to the position in the device. Our study approaches the Cs2AgBiBr6 double perovskite solar cell from an F-P cavity perspective and shows the light trapping phenomenon of the device according to the optical path length modulation.

Validating light phenomena conceptual assessment through the lens of classical test theory and item response theory frameworks

The light phenomena conceptual assessment (LPCA) is a conceptual survey of light phenomena that has been recently established by physics education research (PER) scholars. Studying the LPCA psychometric properties is imperative to inform its measurement validity to potential LPCA users as well as general educational researchers. Classical test theory (CTT) and item response theory (IRT) are two popular statistical frameworks that can be utilized to explore the LPCA measurement validity. To our knowledge, no PER studies have attempted to make a head-to-head comparison of these methods while validating the LPCA. This study is the first to delineate the LPCA measurement by statistically comparing CTT- and IRT-based analyses. The LPCA dataset was drawn from physics students from eight secondary schools presented by Ndihokubwayo and Uwamahoro (2020 Phys. Educ. 55 035009). Our results accomplish harmony between the CTT and IRT arguments to estimate the LPCA item performance and student ability probed by the LPCA. They support the idea that the LPCA may be used as an inventory for evaluating conceptual understanding of light phenomena from the low to high ability range of students, and even some LPCA items should be flagged based on CTT- and IRT-based validity arguments. Special considerations for further refinement related to the discriminating power of problematic LPCA items are discussed.

Adversarial catoptric light: An effective, stealthy and robust physical‐world attack to DNNs

AbstractRecent studies have demonstrated that finely tuned deep neural networks (DNNs) are susceptible to adversarial attacks. Conventional physical attacks employ stickers as perturbations, achieving robust adversarial effects but compromising stealthiness. Recent innovations utilise light beams, such as lasers and projectors, for perturbation generation, allowing for stealthy physical attacks at the expense of robustness. In pursuit of implementing both stealthy and robust physical attacks, the authors present an adversarial catoptric light (AdvCL). This method leverages the natural phenomenon of catoptric light to generate perturbations that are both natural and stealthy. AdvCL first formalises the physical parameters of catoptric light and then optimises these parameters using a genetic algorithm to derive the most adversarial perturbation. Finally, the perturbations are deployed in the physical scene to execute stealthy and robust attacks. The proposed method is evaluated across three dimensions: effectiveness, stealthiness, and robustness. Quantitative results obtained in simulated environments demonstrate the efficacy of the proposed method, achieving an attack success rate of 83.5%, surpassing the baseline. The authors utilise common catoptric light as a perturbation to enhance the method's stealthiness, rendering physical samples more natural in appearance. Robustness is affirmed by successfully attacking advanced DNNs with a success rate exceeding 80% in all cases. Additionally, the authors discuss defence strategies against AdvCL and introduce some light‐based physical attacks.

Prediction of absorptivity in Multi-Jet Fusion manufactured polypropylene structures through laser flash and corrected porosity method

For the first time in the literature, this study validates the absorption phenomena in Multi-Jet Fusion (MJF) printed polypropylene (PP) structures through Laser Flash (LFA) and Corrected Porosity (CP) methods. The influence of process parameters such as build height and build orientation was investigated on tensile properties, crystallinity, porosity and thermophysical attributes in MJF printed PP coupons. Results showed that both crystallinity and tensile performance did not significantly vary with either location or build orientation. Interestingly, samples printed in the Z orientation showed a 35% decrease in strain, indicating that Z-oriented MJF coupons were more brittle than the flat samples (XY). Samples printed in Z orientation also possessed higher porosity and relatively lower crystallinity than the XY orientation. However, large deviations within porosity values were an obstacle to determining a suitable build chamber location for manufacturing dense samples. Therefore, a detailed investigation on porosity of printed samples using micro-CT scans and CT image analysis was necessary. Initially, poor contrast was obvious when MJF printed samples were positioned vertically in the micro-CT chamber which was mainly due to high value of horizontal intensity profile (HIP ~ 70%). Contrast in MJF samples improved significantly in the horizontal orientation (HIP ~ 40%). In parallel, the half-time and heat loss were measured in LFA to understand changes in absorption phenomena with height and orientation of the build. A direct correlation was found between LFA half-time and porosity only when the porosity correction method was implemented. Corrected porosity value was found to be inversely proportional to the heat loss of printed PP samples which indicated higher absorption for samples printed in the bottom of build chamber, XY12, whereas lower absorption was observed for less dense Z samples. Finally, heat loss phenomenon was verified using dense reference Pyroceram samples as they possess high diffusivity and low half-time and porosity compared to MJF printed samples. There is a science behind understanding the absorptivity of the MJF process which is related to the complexity of the process and is challenging to address in MJF PP samples when mixed with carbon black. The study showed that accurately determining the level of porosity is the key to validate absorption phenomena within MJF printed coupons. The contributions of this work are the investigation of the light absorption phenomena in MJF printed PP structures, and the establishment of the absorption-porosity correlation. These contributions help to predict the mechanical properties and subsequently the overall quality of the produced parts which can save cost and time in effectively utilising the MJF process.