Light Diffraction Research Articles

Fluid‐Induced Reconfigurable Polarization‐Insensitive Metasurfaces for Optical Wireless Communications

AbstractIn optical wireless communication (OWC), the adaptability of infrared and visible spectra is attracting growing interest. These technologies are promising solutions for various real‐world applications, including indoor, underwater, vehicular, and IoT systems. However, conventional OWC systems are constrained by their bulky structures and fixed optical properties, which limit their ability to provide on‐demand communication services and integrate with on‐chip technologies. Therefore, the demand for ultrathin, reconfigurable devices with real‐time adaptability is becoming increasingly urgent to ensure efficient and reliable communication. Here, this study introduces a fluid‐induced reconfigurable, polarization‐insensitive metasurface to enhance the performance and flexibility of OWC networks. A key feature is its ability to adjust diffracted light to meet communication requirements, irrespective of the polarization state of the incident light. This metasurface utilizes infrared light at a wavelength of 1550 nm to enhance signal transmission and reduce environmental interference. In a proof‐of‐concept, a 0.5 mm × 0.5 mm metasurface is fabricated, and its focal length variation is verified in three different fluidic environments: Air (n = 1), Polymethyl methacrylate (PMMA) (n = 1.491), and AZ‐GXR (n = 1.602). The proposed design offers reconfigurability, reduced polarization sensitivity, and consistent signal quality, making it ideal for next‐generation OWC applications.

Vectorial acousto-optic Raman–Nath diffraction effect of chiral liquid media

The acousto-optic Raman–Nath (RN) diffraction effects of vector beams diffracted by the chiral ultrasonic grating are demonstrated experimentally and theoretically. The deviation of left- and right-handed circularly polarized components in higher-order diffraction light leads to the rearrangement of their polarization states and intensity due to the different refractive indices of left- and right-hand circularly polarized lights. When the difference between the refractive indices for left- and right-hand circular polarizations is small, linear polarization components of the higher-order diffraction light with the input localized linearly polarized vector optical field rotate compared to the zero-order diffraction light. Novel, to the best of our knowledge, intensity distributions of linear polarization components appear for the input hybridly polarized vector beam.

Defect Structures in Colloidal Crystals and Their Effect on Grating Diffraction Structural Color.

Colloidal crystals of micrometer-sized colloids create prismatic structural colors through the grating diffraction of visible light. Here, we develop design rules to engineer such structural color by specifically accounting for the effect of crystal defects. The local quality and grain size of the colloidal structure are varied by performing self-assembly in the presence of a direct current (DC) electric field. The deposition, self-assembly, and crystallization of these colloids results in polycrystals of variable size, as controlled by the dissolved ion concentration (from 0.01 to 10 mM) and the applied electric current (from 1.6-310 μA/cm2). Under these operating conditions, the global 6-fold crystal bond order parameter (ψ6) of the self-assembled crystals varies from 0.45 ± 0.05 to 0.95 ± 0.01 and the crystal grain number density varies from about 5 to 100 per 0.01 mm2. We find that the grating diffraction structural color intensity of these self-assembled materials is strongly correlated with the crystal quality and grain number, with the diffraction efficiency varying by a factor of ∼2.5 over the range of ψ6 probed. Molecular dynamics (MD) simulation of the electrophoretic deposition reproduces the kinetics of the self-assembly as well as the final structures. It also extends the number and range of deposition conditions probed, thereby creating a library that can be used to study the relationship between defect properties and the grating diffraction structural color. Applying the finite-difference time domain (FDTD) method to solve for light-material interactions in the MD simulated structures yields calculated spectra that agree with experimental observations. The analysis also identifies a design trade-off between diffraction intensity and azimuthal uniformity as order parameter and grain density are varied, thereby demonstrating that the grating diffraction structural color of self-assembled crystals of micrometer-sized colloidal spheres may be controlled by means of their local crystal quality and polycrystallinity.

See-through characteristics of a holographic contact lens display and design consideration for a spatial light modulator

The holographic contact lens display offers an ultra-thin and compact form factor as a visual interface device for augmented reality. It uses a transmission-type spatial light modulator (SLM) and a polarizer to overlay three-dimensional images onto real scenes, affecting the display’s see-through capability. This study explores theoretical and experimental aspects of light efficiency, higher-order diffraction light generation, and see-through image resolution. Increasing the SLM’s fill factor improved the light efficiency and reduced the higher-order diffraction light generation, without impacting the image resolution. Additionally, we investigated removing the polarizer to further enhance light efficiency and demonstrated its effects.

Investigation of the corner rounding effect near the diffraction limit in advanced projection lithography with a rigorous imaging model.

The corner rounding effect in lithography refers to the phenomenon where the corners or angles of a pattern created by lithography are rounded off, rather than remaining square and sharp. This occurs mainly due to the diffraction of light. In addition, mask pattern design, numerical aperture, and the limited resolution of the lithographic process also influence it. The rounding of corners can severely degrade the performance and reliability of microelectronic devices due to incomplete pattern transfer. Therefore, minimizing the corner radius in mask correction is crucial for enhancing pattern fidelity. We propose a methodology that relates the corner radius to the diffraction-limited spot width. By employing aerial image simulation, we delve into the factors that significantly impact the corner radius in projection lithography. By combining a rigorous computational imaging model with the optimization of lithography parameters, the limit of the corner radius is determined in immersion lithography. Our comprehensive investigation reveals the nature of the corner rounding effect, analyzes the contributing factors for corner rounding, and ultimately leads to improvements in imaging quality in photolithography.

A carbon fiber modified with tin oxide/graphitic carbon nitride as an electrochemical indirect competitive immuno-sensor for ultrasensitive aflatoxin M1 detection.

The importance of developing multifunctional nanomaterials for sensing technologies is increasing with the arrival of nanotechnology. In this study, we describe the introduction of novel nanoprobe electro-active material into the architecture of an electrochemical immuno-sensor. Based on the electrochemical immuno-sensor, functionalized tin oxide/graphitic carbon nitride nanocomposite (fSnO2/g-C3N4) was synthesized and then analyte specific anti-aflatoxin M1 monoclonal antibody (AFM1-ab) combined to form an electro-active nanoprobe (fSnO2/g-C3N4/AFM1-ab). First, aflatoxin M1 (AFM1) conjugated bovine serum albumin (BSA-AFM1) was electro-oxidized on the surface of carbon fiber (CF) followed by the consequent addition of nanoprobe. The formation of nanocomposite was substantiated through various characterization techniques, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Dynamic light scattering (DLS). Immuno-sensor fabrication was characterized via Field emission scanning electron microscopy (FE-SEM), optical microscope images, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). This immuno-sensor demonstrated good reproducibility, selectivity, specificity and sensitivity for AFM1 (LOD of 0.03ng mL-1). Following spiking, this immuno-sensor produced good recovery values in the range of 94-96% against real sample, such as milk. The development of sophisticated sensing methods for a range of analytes can greatly benefit from the widespread application of this innovative immuno-sensing approach.

Phase calibration of spatial light modulators using self-generated phase-discontinuity.

In this paper, we introduce a new method for precise determination of the calibration function of liquid crystal spatial light modulators (LC-SLMs). The proposed method shares the advantages of commonly used methods, interferometric and diffraction-based methods, and is free of their disadvantages. The method proposed here is based on the evaluation of Fresnel diffraction of light from a phase-discontinuity pattern loaded into the SLM device. In one version, the phase step pattern consists of two parts, one remains constant at zero, while the other changes with steps of 5 from 0 to 255 gray levels, for each measurement. By fitting the experimental intensity distribution measured in this configuration on the corresponding theoretical intensity distribution, complete phase calibration can be obtained. We also propose a second version, employing a phase wedge pattern, allowing the phase calibration curve of the SLM to be determined by just a single frame measurement which is a great asset.

Diffraction-free partially coherent Pearcey beam.

Partially coherent beams are renowned for their inherent resilience against environmental perturbations. However, traditional versions are prone to distortion due to light diffraction, which presents significant challenges for related applications such as information transfer. In this paper, we theoretically and experimentally construct a non-diffraction, partially coherent Pearcey beam. The results clearly demonstrate such a beam remains invariant during propagation under different coherence conditions. The experimental results align closely with the theoretical predictions. We believe that this beam has the potential to offer new insights as an information carrier for optical communication and information transmission, particularly in adverse environments.

Unconventional Photo‐Control of Structural Features Using Elliptically Polarized Light

AbstractThe holographic interference of either same‐handed or orthogonal polarized beams is commonly employed in the fabrication of optical elements as it enables the development of an ideal sinusoidal surface modulation by inducing the mass migration of photochromic polymer. However, this approach encounters challenges in producing multiplexed optical elements with a complex surface topography, primarily due to only sinusoidal surface topography which limits control over the feature's shape and size. Here, a versatile approach is demonstrated for fabricating spatially multiplexed optical elements using ellipticity‐controlled orthogonally elliptically polarized (OEP) beams that offer distorted square‐like and rhombus‐like pillars on the azopolymer layer by asymmetric azopolymer migration driven by spatially varying ellipticity and azimuth angle of interference beam. These multiplexed distorted shapes enable selective energy transfer during light diffraction and also induce a phase‐shift to polarization states. Ellipticity control of both writing and interference beams provides an additional degree of freedom for structuring the surface topography of optical elements. Furthermore, a quantitative analysis of the multiplexed OEP surface relief is performed to achieve distinct diffraction properties, thereby rendering its suitability for fabricating complex optical elements.

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.

Bifunctional Design of Ferroelectric-Order and Band-Engineering in Cu:KTN Crystal for Extended Self-Powered Photoelectric Response.

Photoelectric conversion in ferroelectric crystals can support many important applications in modern on-chip technology, but suffering from two problems, low responsive current and narrow responsive range. Especially, wide-gap ferroelectric oxides are only active at short-wavelength ultraviolet region with weak photocurrent at nanoampere levels. Here, a bifunctional design strategy of ferroelectric-order and electronic-band to improve the photocurrent and extend the responsive range simultaneously, is proposed. In a Cu-doped KTa1- xNbxO3 (KTN) perovskite crystal, a conductive channel is constructed by "head-to-head" ferroelectric domains, associated with the emergence of micrometer-scale supercells. In addition, the introduction of Cu+ ion can induce defect levels, thus extending the responsive range beyond the inherent absorption of pure KTN. Through rational device optimization, a record self-powered responsivity of 5.23 mA W-1 is realized in Cu:KTN photodetector, which is two orders of magnitude higher than undoped KTN crystal. The temperature-dependent light diffraction and photocurrent show that the ferroelectric-order is dominated in this photoresponse behavior. Moreover, Cu:KTN detector is active in the broadband range from 390 to 1030 nm, covering ultraviolet, visible, and near-infrared regions. This work provides an effective method for the design of next-generation self-powered photodetectors with ultrahigh responsivity and ultrawide responsive range.

Luminescent Nanocrystal Probes for Monitoring Temperature and Thermal Energy Dissipation of Electrical Microcircuit.

In this work, we present an experimental approach for monitoring the temperature of submicrometric, real-time operating electrical circuits using luminescence thermometry. For this purpose, we utilized lanthanide-doped up-converting nanocrystals as nanoscale temperature probes, which, combined with a highly sensitive confocal photoluminescence microscope, enabled temperature monitoring with spatial resolution limited only by the diffraction of light. To validate our concept, we constructed a simple model of an electrical microcircuit based on a single silver nanowire with a diameter of approximately 100 nm and a length of about 50 µm, whose temperature increase was induced by electric current flow. By driving electric current only along one half of the nanowire, we created a dual-function microstructure, where one section is a resistive heater, while the other operates as a radiator. Such a combination realistically reflects the electronic circuit and its thermal behavior. We demonstrated that nanocrystals distributed around this circuit allow for remote temperature readout and enable precise monitoring of the thermal energy propagation and heat dissipation processes, which are crucial for designing and developing highly integrated electronic on-chip devices.

Resolving viral structural complexity by super-resolution microscopy.

In this review, we discuss different super-resolution microscopy (SRM) techniques employed to study viral structures and virus composition with nanometric resolution. We describe the basic principles of the different microscopy methods utilized to break the light diffraction limit, enabling the study of protein composition in viral structures. Finally, we demonstrate for the first time the differential spatial distribution of two structural proteins in an individual baculovirus using single-molecule super-resolution microscopy. We discuss the future of these powerful methods for virology, medicine, and biotechnology applications.

Physics-informed deep learning for 3D modeling of light diffraction from optical metasurfaces.

We propose an alternative data-free deep learning method using a physics-informed neural network (PINN) to enable more efficient computation of light diffraction from 3D optical metasurfaces, modeling of corresponding polarization effects, and wavefront manipulation. Our model learns only from the governing physics represented by vector Maxwell's equations, Floquet-Bloch boundary conditions, and perfectly matched layers (PML). PINN accurately simulates near-field and far-field responses, and the impact of polarization, meta-atom geometry, and illumination settings on the transmitted light. Once trained, the PINN-based electromagnetic field (EMF) solver simulates light scattering response for multiple inputs within a single inference pass of several milliseconds. This approach offers a significant speed-up compared to traditional numerical solvers, along with improved accuracy and data independence over data-driven networks.

Liposomal and Nanostructured Lipid Nanoformulations of a Pentacyclic Triterpenoid Birch Bark Extract: Structural Characterization and In Vitro Effects on Melanoma B16-F10 and Walker 256 Tumor Cells Apoptosis.

Background/Objectives: Pentacyclic triterpenoids are increasingly studied as anticancer agents with many advantages compared to synthetic chemotherapeutics. The aim of this study was to prepare liposomal and nanostructured lipid formulations including a standardized extract of silver birch (Betula pendula) outer bark (TTs) and to evaluate their potential as anticancer agents in vitro, using Melanoma B16-F10 and Walker carcinoma cells. Methods: Appropriate solvents were selected for efficient TTs extraction, and original recipes were used to obtain Pegylated liposomes and nanolipid complexes with entrapped TTs, comparative to pure standards (betulinic acid and doxorubicin) in similar conditions. The composition, morphology, and sizes of all nanoformulations were checked by high-performance liquid chromatography/mass spectrometry, Transmission Electronic Microscopy, and Diffraction Light Scattering. The entrapment efficiency and its impact on cell viability, cell cycle arrest, and apoptosis by flow cytometry was also measured on both cancer cell lines. Conclusions: The standardized TTs, including betulin, lupeol, and betulinic acid, showed good stability and superior activity compared to pure betulinic acid. According to experimental data, TTs showed good entrapment in liposomal and NLC nanoformulations, both delivery systems including natural, biodegradable ingredients and enhanced bioavailability. The apoptosis and necrosis effects were more pronounced for TTs liposomal formulations in both types of cancer cells, with lower cytotoxicity compared to Doxorubicin, and can be correlated with their increased bioavailability.

Synergistic Nonreciprocity of Linear and Nonlinear Optical Diffraction.

Linear optical diffraction of light is a basic natural phenomenon subject to a long history study and it obeys the well-known reciprocity in transport. In this work we report observation of synergistic nonreciprocal linear and nonlinear diffraction of a Ti:sapphire femtosecond laser beam against a periodic poled lithium niobate (PPLN) thin plate nonlinear grating with a front surface corrugated with a shallow grating of a depth only 67nm and a smooth back surface. A high peak power pump laser beam shining upon the geometrically asymmetric nonlinear grating from either the front surface and back surface will both cause significant second-order nonlinear (2nd-NL) Raman-Nath diffraction and Cerenkov radiation, in addition to apparent linear optical diffraction and modest third-order nonlinear (3rd-NL) spectral broadening. These linear, 2nd-NL, and 3rd-NL optical processes all exhibit significant differences between the front-back forward and back-front backward transport processes, in that the linear and 2nd -NL nonlinear diffraction have distinctly different patterns, while the 3rd-NL spectral broadening extent is different. The apparent synergistic nonreciprocal linear and nonlinear diffraction can be ascribed to the different coupling strength between the linear, 2nd -NL, and 3rd-NL processes of pump laser within the PPLN nonlinear grating in the forward and backward pump. The observation of both strong nonreciprocal linear and nonlinear optical diffraction would enrich the concept and physics of fundamental optical reciprocity and nonreciprocity laws.

Boundary-artifact-free quantitative phase imaging with Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) enables high-resolution, wide-field imaging of both amplitude and phase, presenting significant potential for applications in digital pathology and cell biology. However, artifacts commonly observed at the boundaries of reconstructed images can significantly degrade imaging quality and phase retrieval accuracy. These boundary artifacts are typically attributed to the use of the fast Fourier transform (FFT) on non-periodic images. Another significant physical factor that should not be overlooked is the transverse diffraction of light across boundaries. Here, we introduce a boundary extension reconstruction framework for FPM, termed BE-FPM, which provides boundary-artifact-free quantitative phase imaging (QPI) with minimal computational overhead. In this method, the reconstructed image is initialized with zero-padding and then self-extrapolated during the subsequent iterative reconstruction process. This approach allows for partial restoration of the sample beyond the boundary, ensuring sample consistency around the boundary and addressing the boundary artifact problem fundamentally. We demonstrate the effectiveness of the proposed BE-FPM on both microlens array and live cells, establishing it as an effective FPM solver for boundary-artifact-free QPI and accurate phase characterization for various types of samples.

Research on Adjustable Cold View Field Diaphragm in Optical System with Linear Array Detector in AIMS

Abstract The infrared Fourier transform spectrometer needs a cold view field diaphragm to reduce stray radiation. For an infrared spectrometer with linear array detectors, the part of the view field diaphragm where the light passes can be regarded as a slit. If the infrared detectors are in small size, the width of the slit is also small, this will cause serious diffraction phenomena. If the width of the view field diaphragm and the optical system are designed by geometric optics theory, the diffraction light cannot be fully received by the detectors, this will cause energy loss. Expanding the width of the view field diaphragm will introduce stray radiation. Meanwhile, spectrometer follow-up optics should be set in cold environments to reduce the infrared background of the instrument. Optical materials have different thermal characteristics, the optical and mechanical structures will deform at low-temperature, and the cold view field diaphragm is installed at room temperature, so it is impossible to guarantee that the cold view field diaphragm remains in its design position when working at low-temperature.
This paper solves the above problems by designing an adjustable cold view field diaphragm installed in its cryogenic vacuum chamber. The width and position of the view field diaphragm can be adjusted when working in cold temperatures, without opening the cryogenic vacuum chamber. Contrasting the interference signal obtained by the detectors in the adjustment process, the system can get the most suitable width and position of the cold view field diaphragm. The above works are based on the spectrometer used in the Accurate Infrared Magnetic Field Measurements of the Sun (AIMS).

Synchrotron computed tomography combined with AI-based image analysis for the advanced characterization of spray dried amorphous solid dispersion particles

Particle engineering aims to design particles with specific properties. A deeper understanding of how particle formation relates to material attributes and process conditions are critical to strengthen knowledge on powder properties and enhance modeling capabilities. New, alternative powder characterization techniques can offer novel and more accurate measures for particle properties, giving more advanced characterization information. In this context, a case study is presented in which spray dried amorphous solid dispersion powders produced by modifying process conditions were characterized by both well-established compendial methods (i.e., laser light diffraction, SEM image analysis, bulk and tapped density, and gas adsorption), as well as a new method combining synchrotron computed tomography (SyncCT) with AI-based image analysis. SyncCT was used to classify and quantify the spray dried particles as hollow spheres and solid particles, giving a more detailed quality measure of the particle shape, as they impact downstream processing differently. Moreover, hollow particle wall thicknesses, as well as internal and external particle surface areas were measured by SyncCT. Altogether, powder characterization data from SyncCT show similar trends to that obtained from compendial techniques and giving additional quality measure regarding particle shape, showing promise of this new and advanced characterization method.

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.