Light Diffusion Research Articles

Recent Progress in Block Copolymer Self-Assembly for the Fabrication of Structural Color Pigments.

The self-assembly of block copolymers (BCPs) into photonic materials has garnered increasing interest due to the versatility and ease of fabrication offered by the synthesized building blocks. BCPs are highly tunable, with their self-assembled structures' size being adjustable by modifying the block lengths, molecular weight(Mw), and polymer composition. This review provides a concise summary of the use of BCPs as photonic pigments, which generate color through structural manipulation rather than relying on chemical pigmentation. These photonic crystal pigments manipulate light behavior, including interference, diffraction, and diffusion, to generate specific colors. BCPs are categorized into two types: linear block copolymers (LBCPs) and brush block copolymers (BBCPs), each involving different monomers that form photonic crystals(PCs). The structural evolution and advancements of BCPs in various practical applications are also explored. It concludes by suggesting that structural color(SC) pigments based on eco-friendly PCs may replace traditional chemical ones in fields such as printing ink, biosensing, chemical sensing, and adaptive photonic materials.

Method for simultaneous reconstruction of a depth and clear image with a single blurred image in microscopy

The evaluation of imaging blur degradation characteristics of high-magnification optical microscopes is greatly influenced by complex imaging mechanisms, image textures, and illumination, which seriously limit the observation precision at the micro-nano scale. This paper proposes a method for simultaneous reconstruction of the depth and clear image of a blurred image based on the light intensity distribution law of the microscopic imaging system. First, based on the diffraction characteristics of the light in the circular stable cavity, the light intensity distribution function on the imaging plane of the imaging system is established, and the law of the light intensity diffusion degree with the scene depth variation is obtained by curve fitting, that is, the 3D blur degradation model of the system. Secondly, the normalized blurring degree of blurred images with different textures and different illuminations is calculated, and the mapping relationship between the blurring degree of different images and the light intensity diffusion degree of the system is established with the depth change as the intermediate variable. Thirdly, an adaptive spectral clustering method is introduced to classify the blurred images, and the weighted K-nearest neighbor method is used to automatically classify any blurred image and calculate its normalized blurring degree value and the corresponding system energy diffusion value. Based on the 3D blur degradation model and the normalized blurring degree, the depth calculation of the blurred image and the reconstruction of the clear image are realized simultaneously. The precision of the method proposed in this paper is verified by various standard nano-scale grid images and various real biological tissue samples.

InSitu Measurements of Light Diffusion in an Optically Dense Atomic Ensemble.

This study introduces a novel method to investigate insitu light transport within optically thick ensembles of cold atoms, exploiting the internal structure of alkaline-earth metals. A method for creating an optical excitation at the center of a large atomic cloud is demonstrated, and we observe its propagation through multiple scattering events. In conditions where the cloud size is significantly larger than the transport mean free path, a diffusive regime is identified. We measure key parameters, including the diffusion coefficient, transport velocity, and transport time, finding a good agreement with diffusion models. We also demonstrate that the frequency of the photons launched inside the system can be controlled. This approach enables direct time- and space-resolved observation of light diffusion in atomic ensembles, offering a promising avenue for exploring new diffusion regimes.

Composition of Quantum Dot Color Conversion Layer with ZnS Nanoparticle for Facile Ink Formulation and Uniform Inkjet Printing

Quantum dot (QD) is excellent material for next-generation displays because of their superior optical properties, such as high quantum efficiency, narrow full width at half maximum, high color purity, and photoluminescence quantum yield. QD demonstrated efficient absorption of blue light, coupled with high color-conversion efficiency, fabricated them suitable for use as color-conversion layers (CCLs). However, robustness in pixel patterning uniformity and a printing resolution should be further studied. Light emission via conversion through QD films or converter pixels still need to be improved because the blue light can directly transmit the QD layers, sometimes leading to insufficient energy to excite the QDs. Thus, many studies on QD CCLs have focused on improving the absorption and emission properties of QDs, formulating CCL resins with enhanced color conversion efficiency. Scattering can alter the optical path and incident angle of the emitted light to increase internal reflection so that light emission of the optical film can be enhanced for excitation of photons. Thus, light scattering particles, such as titanium dioxide (TiO2), silicon dioxide (SiO2), zinc oxide (ZnO), and zirconium oxide (ZrO2) were carefully tuned to achieve outstanding properties as QD CCLs, increasing color conversion efficiency.In this work, zinc sulfide (ZnS) light diffusers with hydrophobic properties and various size distribution were synthesized. ZnS and QD were mixed in acrylic resin, isobornyl acrylate, with proper composition of initiator and photocrosslinker. The recipe of mixing was considered for a fabrication of QD CCL ink with optimum viscosity, dispersion stability and uniformity, and printability. For the QD-CCL ink with relatively high viscosity, evaluation of jetting profile and pixel-patterning was conducted with commercial ink cartridge, Sapphire QE-256/30AAA (Fujifilm), combined with the custom-built inkjet printer and high-speed camera. With the scale up to 200ppi QD-CCL pattern, the color spectrum, printability, dispersion, optical properties (evaluation of color-emitting image), and surface uniformity were evaluated. Overall, this work will demonstrates the enhanced light converion behavior of QD-CCL layer fabricated by inkjet-printing process and provide a novel evaluation prorocol of uniformity for QD-CCL layer and color conversion device using blue micro-LED.

Development of α-ray visualization survey meter in high gamma and neutron background environment.

A survey meter was developed to reliably detect and visualize surface contamination of suits and objects by α-nuclides in high γ/n-rays background radiation environment. The survey meter features a semi-opaque ZnS:Ag scintillator mounted directly onto a multi-anode photomultiplier tube (MA-PMT) and amplification circuits, ensuring output gain equalization for all channels. α-ray events induce localized light emission in thin-film scintillators. By directly mounting the scintillator, diffusion of light before reaching the MA-PMT is suppressed, concentrating it in just a few channels, thereby facilitating discrimination from background radiation. This design also enables clear visualization of the shape of surface contamination. The prototyped survey meter is capable of responding up to 2.1×107cpm, with no γ-ray response even in high-radiation environments exceeding 1Sv/h. In actual environments with high background radiation, contamination of ~1/100th of the surface contamination density limit of 4Bq/cm2 could be reliably detected.

Ibuprofen encapsulation inside non-conventional O/W Pickering emulsions stabilized with partially hydrophobized silica

The encapsulation of active ingredients is an important process in various industrial sectors including pharmaceutics, foods and cosmetics. For the first time, the capacity of non-conventional anti-Bancroft oil-in-water Pickering emulsions stabilized by partially hydrophobized silica to encapsulate an apolar active is addressed. A dispersed phase volume of paraffin oil of 50% coupled to 0.5 wt.% of silica has been employed to avoid excess of silica in the continuous phase and encapsulate higher amount of ibuprofen (the model drug). Three ibuprofen contents ranging from 100 mg (1.6 mg/mL of paraffin) to 420 mg (6 mg/mL of paraffin) have been tested. The encapsulation efficiency as well as the emulsions properties are investigated by the means of light diffusion, microscopy, rheology, and HPLC coupled to mass balance. The Pickering emulsion is very efficient for the encapsulation of ibuprofen with encapsulation rates of 99% obtained inside droplets of 30 µm for all the 3 ibuprofen concentrations. This encapsulation ability is perfectly maintained, whether during ageing (during 90 days), or when the emulsion is diluted by a factor 100 inside physiological media at basic and acidic pH.

Investigating the pH-Dependence of gelation process in chitosan-glutaraldehyde hydrogels with diffusing wave spectroscopy

The gel time of functional hydrogels is an essential property that dictates their utility in various applications. To accurately assess this parameter, the chitosan-glutaraldehyde hydrogels were characterized here using two complementary analytical tools, rotational rheometer, and diffusing wave spectrometer (DWS). Rotational rheometers are widely used to continuously monitor the macro-mechanical properties of hydrogels during the gelation process. By observing the modulus change curve, one can gain insights into the instantaneous changes occurring within the gel network. This method provides a direct measurement of the gel's mechanical strength; however, it involves applying external forces to the sample, which may introduce artifacts such as measurement lag and potential sample deformation or destruction. Results of this study indicated that the application of external force during rotary rheometer measurements disrupted the gelation process. In contrast, DWS detected alterations in the microstructure by measuring light diffusion, allowing to track microstructural changes post-crosslinking, and curing without the interference of external stress. Thus, DWS offers a non-invasive approach to studying gelation as it detected the Brownian motion of particles within the hydrogel by monitoring the diffraction of light, thereby providing undisturbed dynamic information about the gel's behavior. The DWS technique is particularly useful for tracking microstructural changes that occur during hydrogel crosslinking and curing, without altering the gel's native state. An additional advantage of DWS is its ability to investigate the pH effect on gelation. By measuring changes in gelation time as a function of pH, we could achieve precise control over the gelation process. This fine-tuning of gelation kinetics is crucial for applications that require rapid or delayed gelation, offering a level of precision that is difficult to match with traditional rheological methods.

Transverse dynamics of charmed hadrons in ultra-relativistic nuclear collisions

Transverse momentum pT spectra and anisotropic flow distributions are studied for charmonia and charmed hadrons produced in Pb-Pb collisions and measured with the ALICE detector at the CERN Large Hadron Collider (LHC). The investigations are performed within the framework of the Statistical Hadronization Model with the transverse dynamics evaluated using predictions from relativistic viscous hydrodynamics as implemented in the computer codes MUSIC and FluiduM. With this essentially parameter-free approach good agreement is obtained for pT spectra in the range pT < 10 GeV/c. The observed wide distribution in pT of anisotropic flow coefficients v2 and v3 for charmonia is also well reproduced, while their magnitude is generally somewhat over predicted. This finding may be connected to a difference in spatial distribution between light and charmed hadrons due to a different diffusion of light and heavy quarks in the hot fireball.

Novel polystyrene‐based light diffusing materials: Introduction of magnesium hydroxide to enhance scattering range and thermal conductivity

AbstractIn high‐power lighting, large‐screen display, and other practical application scenarios, Light diffusing materials (LDMs) with favorable thermal conductivity are desired to assist in heat dissipation. In this paper, platy magnesium hydroxide (pMH) and mesoporous spherical magnesium hydroxide (sMH) were introduced as scattering particles for the first time to prepare polystyrene (PS)‐based LDMs. The limited refractive index mismatch allowed MH to be filled in large quantities with less sacrifice of light transmission performance. Owing to the complex surface morphology and large specific surface area, sMH possesses stronger scattering capability, and its combination addition with pMH could effectively increase scattering range. Meanwhile, an effective filler network was constructed with the combined use of pMH and sMH, and thus enhanced the thermal conductivity of the composites. Additionally, PS/pMH‐sMH composites exhibited higher thermal stability. This study expands the auxiliary thermal management capability of light diffusion materials and presents a new application possibility for MH as scattering particles.Highlights A new application possibility for Magnesium hydroxide as scattering particles. Light transmittance degradation of PS/MH at high filler loadings was mitigated by RI matching. Complex surface morphology endowed sMH with strong scattering capability. Optimal filling ratio of pMH to sMH was tested for better scattering performance. Extended scattering range, improved TC and thermal stability was achieved.

Revolutionizing superhighway traffic board lighting with remote LED spotlights

In this paper, we present a groundbreaking approach to enhance the illumination of traffic boards along superhighways, addressing significant challenges associated with conventional lighting systems. Our innovative method revolves around the strategic placement of remote spotlights at the side of the roadway to illuminate traffic signs equipped with retroreflector film (RTRF). The essence of our approach lies in remote illumination, which requires meticulous adjustment of the divergence angle of the spotlights to match the size of the signs and their distance from the projection source. To achieve the desired spotlight configuration, we have developed a hybrid optical system that incorporates a paraboloid reflector and a lens mounted on a bridge holder situated on top of the mirror. Through spot light illumination, we discovered that the initial divergence angle of the RTRF was too narrow. To improve projection angle tolerance, we recommend attaching a light diffuser film onto the surface of the RTRF. The coverage area ratio of the diffuser film can be adjusted to select the desired divergence angle for the reflected light. Our experimental measurements have yielded significant results, showcasing the half-divergent angle of the RTRF ranging from 3° to 7° for different coverage area ratios of the diffuser. In practical terms, with a target luminance of 300 nits at the white word on the traffic board, the power consumption of the spotlight fixture of the roadway was only 40 W, representing over 75% power savings when compared to traditional lighting methods. Consequently, our approach opts to utilize spotlights for illuminating specific traffic boards on superhighways, offering a more efficient and manageable lighting solution that greatly benefits both motorists and road maintenance personnel.

Two-dimensional hierarchically porous C3N4 for photocatalysis: perspective and challenges

Owing to its unique structure, porosity and photoresponse properties, two-dimensional hierarchically porous (2D-HP) C3N4 has attracted wide attention in environmental remediation and sustainable energy evolution fields. Up to today, 2D-HP C3N4 has been developed as an efficient photocatalyst for various environmental/energy photocatalytic applications. Its advantages in promoting light harvesting, reactant diffusion and transportation, surface molecule activation and photoinduced carrier separation have been verified. In this perspective, we highlighted the advantages of 2D-HP C3N4 in various photocatalytic reactions such as water splitting and H2O2 production. The relevant mechanism was simultaneously discussed. Moreover, the prospects and obstacles for the industrial utilization of 2D-HP C3N4-based photocatalysts are outlined and summarized. Finally, we envision available approaches for the deployment of 2D-HP C3N4-based materials to promote its practical application.

Realization of Time-Reversal Invariant Photonic Topological Anderson Insulators.

Disorder, which is ubiquitous in nature, has been extensively explored in photonics for understanding the fundamental principles of light diffusion and localization, as well as for applications in functional resonators and random lasers. Recently, the investigation of disorder in topological photonics has led to the realization of topological Anderson insulators characterized by an unexpected disorder-induced phase transition. However, the observed photonic topological Anderson insulators so far are limited to the time-reversal symmetry breaking systems. Here, we propose and realize a photonic quantum spin Hall topological Anderson insulator without breaking time-reversal symmetry. The disorder-induced topological phase transition is comprehensively confirmed through the theoretical effective Dirac Hamiltonian, numerical analysis of bulk transmission, and experimental examination of bulk and edge transmissions. We present convincing evidence for the unidirectional propagation and robust transport of helical edge modes, which are the key features of nontrivial time-reversal invariant topological Anderson insulators. Furthermore, we demonstrate disorder-induced beam steering, highlighting the potential of disorder as a new degree of freedom to manipulate light propagation in magnetic-free systems. Our work not only paves the way for observing unique topological photonic phases but also suggests potential device applications through the utilization of disorder.

Functional light diffusers based on hybrid CsPbBr3/SiO2 aero-framework structures for laser light illumination and conversion

The new generation of laser-based solid-state lighting (SSL) white light sources requires new material systems capable of withstanding, diffusing, and converting high intensity laser light. State-of-the-art systems use a blue light emitting diode or laser diode in combination with color conversion materials, such as yellow emitting Ce-doped phosphors or red and green emitting quantum dots (QD), to produce white light. However, for laser-based high-brightness illumination thermal management and uniform light diffusion are still major challenges in the quest to convert a highly focused laser beam into an efficient lighting solution. Here, we present a material system consisting of a highly open porous (> 99%) framework structure of hollow SiO2 microtubes. This framework structure enables efficient and uniform light distribution as well as ensuring good thermal management even at high laser powers of up to 5 W, while drastically reducing the speckle contrast. By further functionalizing the microtubes with halide perovskite QDs (SiO2@CsPbBr3 as model system) color conversion from UV to visible light is achieved. By depositing an ultrathin (~ 5.5 nm) film of poly(ethylene glycol dimethyl acrylate) (pEGDMA) via initiated chemical vapor deposition (iCVD), the luminescent stability of the QDs against moisture is enhanced. The demonstrated hybrid material system paves the way for the design of advanced and functional laser light diffusers and converters that can meet the challenges associated with laser-based SSL applications.Graphical

Bijel-based mesophotoreactor with integrated carbon nitride for continuous-flow photocatalysis

The integration of continuous-flow technologies with heterogeneous photocatalysis has recently emerged as a promising strategy for the development of sustainable processes. Although conventional packed bed reactors have been extensively utilized in industrial catalytic applications, they face challenges related to energy transfer in the photocatalytic systems. This study presents an innovative approach to address this issue by integrating heterogeneous photocatalysts with an organic polymer, leading to the fabrication of a mesophotoreactor featuring a bijel-based structural configuration. This novel strategy involves hybridizing polypentadecalactone and in situ confining of carbon nitride in a bicontinuous porous mesoarchitecture. The structural and physicochemical properties of the resulting catalytic composite material are evaluated through an array of characterization methods, affirming the successful integration of carbon nitride within the overall structure. The unique bicontinuous porous architecture of the composite and its suitability for industrial applications is verified, as exemplified by its exceptional efficiency in the photodegradation of methylene blue (>99 %) under flow conditions and remarkable stability up to three reaction cycles. A mathematical model is developed to describe continuous photocatalytic processes occurring in the novel tubular mesophotoreactor, with a specific focus on the degradation of the methylene blue dye. This model is successfully validated, leading to results in agreement with the experimental measurements. Additionally, fluid dynamics simulations demonstrate that the mesophotoreactor design allows for the effective diffusion of light through its channels, resulting in higher irradiation levels compared to conventional systems such as packed bed reactors. The innovative design of the catalytic reactor presented in this work offers a versatile and efficient alternative to the conventional heterogeneous systems, significantly broadening the range of applications for photocatalytic processes.

Ultra high-speed 3D shape measurement technology for specular surfaces based on μPMD

Phase measuring deflectometry (PMD) has been extensively applied to measure specular surfaces due to its non-contact, high-precision, full-field measurement capabilities. Liquid crystal display (LCD) screen is the most common structured light source in PMD. However, the response time of liquid crystal molecules limits its frame rate to around 100 frames per second (fps). Therefore, it is quite difficult for traditional PMD to measure rapidly moving surfaces. This paper proposes a 3D dynamic sensing technique, microsecond-PMD (µPMD) based on the high-frame-rate sinusoidal fringe display (HSFD). In the proposed method, the switching time for each fringe pattern display is at a sub-microsecond level, enabling high-speed fringe acquisition with kHz-level area array detection or 100kHz-level line array scanning. The HSFD method uses a specially designed LED array and two-step optical expansion. The high-speed switching characteristic of LED sources is utilized to allow a superfast display rate. Moreover, the superior sinusoidal property can be achieved by the combination of the specially designed discrete sinusoidal LED array, the light-diffracting effect of orthogonal gratings, and the filtering effect of the light diffuser. The mechanism and analytic model of fringe generation are thoroughly analyzed and discussed in this work. Furthermore, the swarm optimization algorithm and corresponding weighted fringe quality evaluation function are presented to obtain the optimal fringes. To the best of our knowledge, the proposed µPMD, for the first time, achieved a superfast fringe acquisition rate of 4000fps with sub-micrometer precision in three-dimensional (3D) reconstruction for specular surfaces. We envision this proposal to be broadly implemented for real-time monitoring in manufacturing.

Photonic Mpemba effect.

The Mpemba effect (ME) is the counterintuitive phenomenon in statistical physics for which a far-from-equilibrium state can relax toward equilibrium faster than a state closer to equilibrium. This effect has raised great curiosity for a long time and has been studied extensively in many classical and quantum systems. Here, it is shown that the Mpemba effect can be observed in optics as well. Specifically, the process of light diffusion in finite-sized photonic lattices under incoherent (dephasing) dynamics is considered. Rather surprisingly, it is shown that certain highly localized initial light distributions can diffuse faster than initial broadly delocalized distributions. The effect is illustrated by considering the random walk of optical pulses in fiber-based temporal mesh lattices, which should provide an experimentally accessible setup for the demonstration of the Mpemba effect in optics.

STAR-FDTD: space-time modulated acousto-optic guidestar in disordered media

Abstract We developed a 2D Finite-difference time-domain (FDTD) method for modeling a space-time modulated guidestar targeting wavefront shaping applications in disordered media. Space-time modulation in general (a particular example being the acousto-optic effect) is used here as a guidestar for the transverse confinement of light around the tagged region surrounded by disorder. Together with the guidestar, the iterative optical phase conjugation (IOPC) method is used to overcome the diffusion of light due to multiple scattering. A phase sensitive lock-in detection technique is utilized to estimate the steady-state amplitude and phase of the modulated wavefronts emerging from the guidestar region continuously operating in the Raman-Nath regime. As the IOPC scheme naturally converges to the maximally transmitting eigenchannel profile, one could use the position of the guidestar within the disorder to channelize the maximal transmission through the tagged region. The associated code developed in MATLAB® is provided as an open source (The MIT License) package. The code package is referred by the acronym STAR-FDTD where STAR stands for Space-Time modulated Acousto-optic guidestaR.

Exploring visible spectrum wavelengths in light transmission through wood material

Wood is a multiscale heterogeneous natural composite material with properties depending on its growing conditions and its genetic heritage. This variability is challenging for industries that work to perform homogeneous and reliable products. In industry, different non-destructive testing methods are in use to classify, grade, and select wood products to optimize their usage. Among them, the use of lasers to detect fiber orientation with different wavelengths. This orientation significantly influences the mechanical behavior of wood, including stress limits and stiffness. According to our knowledge, the use of laser diffusion still is limited to grain angle measurement. Our objective in this paper is to realize transmission light scattering maps for wood samples from several wood species (poplar, oak, Douglas fir, beech), and then identify the most suitable wavelength to study light diffusion in wood, depending on the property that will be measured. A supercontinuum laser is used over a wavelength range from 500 to 800 nm, allowing precise adjustment of the wavelengths. It was found that near-infrared light better scatters in the studied wood species than lower wavelength. However, the wavelength that gives the best contrast between earlywood and latewood depends on the sample studied and is not necessarily in the near infrared rays.

Development of single-sided structure collimation film for direct-lit collimated backlight module.

In this paper, we proposed an optical structure to enhance the collimation and uniformity of 405 nm LED backlight modules. The structure is called a single-sided structure collimation film (SSSCF), which consists of a lenticular lens array, slit apertures, and a highly reflective coating surface. A lenticular lens array with slit apertures converts the angle of diffusive incident light into collimated light. The high-reflective coating of the collimation film can reflect back the light that does not enter the slit aperture to the backlight module for energy recycling. Finally, we have developed a direct-lit backlight module with optimized collimation properties (FWHM = ±3.4°, gain = 2.3%, NSR = 0) and great uniformity (uniformity > 83.5%). We also demonstrated good consistency between our simulation results with optical measurement. The collimated backlight module developed in this study has great potential for future applications, including high-precision 3D printing objects, liquid crystal displays with high contrast ratio or narrow viewing angles, and telecentric illumination devices used in precision machine vision systems.

Dynamic viscosity, interfacial tension and diffusion coefficient of n-hexane, cyclohexane, 2-methylpentane with dissolved CO2

In this work, n-hexane, cyclohexane and 2-methylpentane were selected to represent linear-alkane, cycloalkane and branched-alkane, respectively. Based on the dynamic light method (DLS), the viscosity, interfacial tension and diffusion coefficient of n-hexane/CO2, cyclohexane/CO2 and 2-methylpentane/CO2 systems under saturation condition were measured in order to explore the change trend of thermophysical properties of the systems with the same carbon atom number but different molecular structures. The experiments were conducted at the temperatures of 303, 343 and 383 K and at pressures up to 5.64 MPa. The expanded uncertainties（k = 2）of dynamic viscosity, interfacial tension and diffusion coefficient were 3 %, 3 % and 4.4 % respectively. The experimental results show that n-hexane and 2-methylpentane with similar molecular structure have more similar value of the properties. The effects of different alkane structures on system viscosity, interfacial tension, and diffusion coefficient were explained at the molecular level through radial distribution function, interface thickness, and CO2 coordination number. At 303.15 K and 4 MPa, the peak radial distribution function of CO2/cyclohexane is 1.845, which is greater than that of CO2/n-hexane and CO2/2-methylpentane molecules. It has been proven that the arrangement of CO2/cyclohexane is more orderly, resulting in higher viscosity and lower diffusion coefficient of the system. The interface thickness of CO2/cyclohexane is 6.13 nm, which is smaller than CO2/n-hexane (7.53 nm) and CO2/2-methylpentane (6.3 nm). The smaller the interface thickness, the more compact the structure, the stronger the intermolecular forces, and the greater the interfacial tension. At 303.15 K and 2 MPa, the number of CO2 coordination sites within 1 nm around liquid phase alkanes is 3.96, which is smaller than 4.78 for cyclohexane and 6.62 for 2-methylpentane. Prove that the coordination number is directly proportional to the diffusion coefficient and inversely proportional to viscosity and interfacial tension.