Optical Approach Research Articles

Solution-Processed Metallic Nanowire Network for Wearable Transparent Thermal Radiation Shield.

Heating requirements for residential and commercial dwellings result in significant energy consumption and deleterious environmental effects. Personal radiative thermal management textiles regulate the wearer's body temperature by controlling the material's intrinsic optical properties. Passive heating textiles suppress radiative heat losses and therefore significantly reduce the energy consumption required for building heating systems. Guided by an optical theoretical approach, a transparent radiation shield (TRS) is designed based on silver nanowires (AgNWs) that can suppress human body heat with simultaneous visible light transmittance anticipated for practical fabrics. We experimentally demonstrated a TRS with large infrared light reflectance (low emissivity of 35%) and a visible (VIS) transparency value of 75% (400-800 nm). The results are well corroborated by the Mie scattering theory and the wire-mesh equivalent sheet impedance model, which provide fundamental mechanism understanding and guidance toward higher performance. The TRS is fabricated by a simple, solution-processing method with thermoplastic elastomer protective layers, granting notable stretching capabilities, mechanical robustness, and conformability to any body shape or object. The rigorous theoretical strategy enables the scalable synthesis of low-emissivity and visibly transparent textiles for personal thermal comfort.

Dielectrophoresis: Measurement technologies and auxiliary sensing applications.

Dielectrophoresis (DEP), which arises from the interaction between dielectric particles and an aqueous solution in a nonuniform electric field, contributes to the manipulation of nano and microparticles in many fields, including colloid physics, analytical chemistry, molecular biology, clinical medicine, and pharmaceutics. The measurement of the DEP force could provide a more complete solution for verifying current classical DEP theories. This review reports various imaging, fluidic, optical, and mechanical approaches for measuring the DEP forces at different amplitudes and frequencies. The integration of DEP technology into sensors enables fast response, high sensitivity, precise discrimination, and label-free detection of proteins, bacteria, colloidal particles, and cells. Therefore, this review provides an in-depth overview of DEP-based fabrication and measurements. Depending on the measurement requirements, DEP manipulation can be classified into assistance and integration approaches to improve sensor performance. To this end, an overview is dedicated to developing the concept of trapping-on-sensing, improving its structure and performance, and realizing fully DEP-assisted lab-on-a-chip systems.

Gold nanoparticles assisted colorimetric sensing of paroxetine, duloxetine, and olanzapine in aqueous and micellar systems with improved sensitivity

The present study explored a rapid and facile colorimetric identification of two antidepressants (paroxetine and duloxetine) and one antipsychotic drug (olanzapine) in aqueous and micellar systems using citrate-stabilized gold nanoparticles (Cit-AuNPs). The sensing approach involved hydrogen bonding and electrostatic interactions on the surface of Cit-AuNPs. The attributes of Cit-AuNPs and their interactions with the drugs were probed using characterization techniques like UV–Vis spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential measurement, and Fourier-transform infrared spectroscopy (FT-IR). Various factors including the volume of Cit-AuNPs, pH, reaction time, surfactant concentration, and the sequence of addition of reagents were optimized to inspect their impacts on sensing results. Under optimized conditions, the probe showed good linearity for the three drugs at the nanomolar (nM) range. Consequently, the color of the Cit-AuNP solution transformed from red to royal purple and blue, which was visible to the naked eye and monitored by visible absorption spectra. This label-free optical detection approach could recognize paroxetine (Prx), duloxetine (Dlx), and olanzapine (Olz) in aqueous system at concentrations ranging from 1 to 17 nM with a limit of detection (LOD) of 0.312, 0.258, and 0.418 nM (S/N = 3), respectively. Meanwhile, the sensitivity was improved in the Triton X-100 (TX-100) micellar system with LOD of 0.029, 0.030, and 0.029 nM for Prx, Dlx, and Olz, respectively accompanied by a shift in the absorption bands. The micellar system contributes stability to the Cit-AuNP-drug complex. The devised colorimetric approach was convenient and did not require any complex equipment. It was efficaciously used to detect three drugs in pharmaceutical products, spiked human urine, and blood serum samples with satisfactory recoveries of 99.83–103.45% and RSD < 3.5%. Notably, the sensing assay demonstrated good selectivity for three drugs in the existence of commonly encountered foreign species and certain common drugs with a relative error below 3%. The results of the present study were statistically compared with reference methodology. The results were validated with no significant difference between the devised and reported approaches considering precision and accuracy, respectively.

Feasibility of Using SWIR-Transformed Reflectance (STR) in Place of Surface Temperature (Ts) for the Mapping of Irrigated Landcover

(1) Background: A simple approach to map irrigated landcover has been introduced by using measures derived from the optical spectral range as an alternative to the thermal range. It has been demonstrated that substituting surface temperature (Ts, ‘thermal approach’) with SWIR-transformed reflectance (STR, ‘optical approach’) to detect surface moisture is feasible with comparable results. (2) Methods: Using an iterative thresholding procedure to minimize within-class variance, the bilevel segmentation of variables derived from Landsat-8 representing surface moisture and vegetation cover was achieved for the 2020–2021 summer for a key irrigation district in Australia. (3) Results: The results of irrigated landcover by the optical approach were found to be comparable with those obtained by the thermal approach. The classification accuracy was assessed using water delivery records at the farm level. Although the overall accuracy was high in both cases, the optical approach (97.6%) performed slightly better than the thermal approach (93.9%). (4) Conclusions: The feasibility of using STR to map irrigated landcover has been confirmed by a high-level overall accuracy assessment. This has broader implications in terms of irrigated landcover assessment, as the use of satellite imagery in these applications may not necessarily be limited to microwave or thermal sensors.

Instantaneous thermometry imaging using two-photon laser-induced fluorescence.

Measuring temperature in complex two-phase flows is crucial for understanding the dynamics of heat and mass transfer. In this Letter, we introduce a novel, to the best of our knowledge, optical approach based on the combination of two-photon laser-induced fluorescence (2p-LIF) imaging and two-color laser-induced fluorescence (2CLIF) for instantaneous temperature mapping of complex liquid media. Using Kiton Red (KR) and Rhodamine 560 (R560), a temperature sensitivity of 1.54%/∘C has been achieved over a range of 17-60°C. The monitoring of two-dimensional transient temperature dynamics in the heating and degassing of water shows the efficiency of the 2p-2CLIF. This new approach contributes to the toolkit of optical temperature measurement techniques, providing a robust solution for studying transient scattering media and high-speed two-phase flows.

Testing a Hyperspectral, Bio‐Optical Approach to Identification of Phytoplankton Community Composition in the Chesapeake Bay Estuary

AbstractThe multi‐to hyperspectral evolution of satellite ocean color sensors is anticipated to enable satellite‐based identification of phytoplankton biodiversity, a key factor in aquatic ecosystem functioning and upper ocean biogeochemistry. In this work the bio‐optical Phytoplankton Detection with Optics (PHYDOTax) approach for deriving taxonomic (class‐level) phytoplankton community composition (PCC, e.g. diatoms, dinoflagellates) from hyperspectral information is evaluated in the Chesapeake Bay estuary on the U.S. East Coast. PHYDOTax is among relatively few optical‐based PCC differentiation approaches available for optically complex waters, but it has not yet been evaluated beyond the California coastal regime where it was developed. Study goals include: (a) testing the approach in a turbid estuary including novel incorporation of colored dissolved organic matter (CDOM) and non‐algal particles (NAP), and (b) performance assessment with both synthetic mixture and field data sets. Algorithm skill was robust on synthetic mixtures. Using field data, cryptophyte and/or cyanophyte phytoplankton groups were predicted, but diatom and dinoflagellate detection was not conclusive. For one field data set, small but significant improvements were observed in predicted PCC groups when tested with incorporation of CDOM and NAP into the algorithm, but not for the second field data set. Sensitivity to three hyperspectral‐relevant spectral resolutions (1, 5, 10 nm) was low for all field and synthetic data. PHYDOTax can identify some phytoplankton groups in the estuary using hyperspectral, field‐collected measurements, but validation‐quality data with broad temporospatial coverage are needed to determine whether the approach is robust enough for science applications.

A novel interferometry-based method to study the anisotropy and kinetics of liquid to solid transition in polymer

We propose and demonstrate a first Twin -interferometry based optical approach for studying and exploring anisotropy and directional dependent crystallization kinetic of curing polymers under isothermal condition. A commercial polymeric solution of polyvinylidene fluoride hexa-fluoropropylene (PVDF-HFP) with five different concentrations were prepared and utilised for this study. A Twin-interferometer (TIM) is designed to record the rate of shift in Michelson’s fringes caused by rate of change of optical path length of a transparent polymeric solution in two orthogonal directions during curing. Pair of interferogram referred as Twin- interferogram (TIG) is recorded for the sample of all concentration during its liquid to solid transition. An extraction approach for various crystallization parameters such as anisotropy, crystallization half-life time, constants governing the rate and dimensionality of crystallization, and their variation along distinct direction from TIM is demonstrated. The results provided by TIM are verified by a method of anisotropy annihilation and other experimental techniques includes Scanning electron microscopic (SEM), Polarising optical microscopic (POM) and Dielectric spectroscopic studies.

Spatial-temporal optical vortex pendulum on a curved surface.

Spatial-temporal optical vortices (STOVs) have recently become the focus of newly structured optical fields. In this paper, their propagation on a 2D curved surface named the constant Gaussian curvature surface (CGCS) is studied. Using the matrix optics approach, we provide the analytical solution of the STOV propagation under the paraxial approximation on the CGCS with positive curvature. One method of creating timers is made possible by the spatiotemporal distribution direction of STOV light intensity, which swings like a pendulum throughout the evolution, in contrast to propagation on a flat surface. This swing, however, stops when the curved surface's curvature radius matches the light's Rayleigh distance. Besides, the transverse orbital angular momentum of STOV is deduced, and we find that the intrinsic and extrinsic OAM periodically exchange, but the total transverse OAM is always zero during the propagation on CGCS. It aids in controlling the transverse extrinsic orbital angular momentum of STOV in nontrivial space.

Viewing early life without labels: optical approaches for imaging the early embryo†.

Embryo quality is an important determinant of successful implantation and a resultant live birth. Current clinical approaches for evaluating embryo quality rely on subjective morphology assessments or an invasive biopsy for genetic testing. However, both approaches can be inherently inaccurate and crucially, fail to improve the live birth rate following the transfer of in vitro produced embryos. Optical imaging offers a potential non-invasive and accurate avenue for assessing embryo viability. Recent advances in various label-free optical imaging approaches have garnered increased interest in the field of reproductive biology due to their ability to rapidly capture images at high resolution, delivering both morphological and molecular information. This burgeoning field holds immense potential for further development, with profound implications for clinical translation. Here, our review aims to: (1) describe the principles of various imaging systems, distinguishing between approaches that capture morphological and molecular information, (2) highlight the recent application of these technologies in the field of reproductive biology, and (3) assess their respective merits and limitations concerning the capacity to evaluate embryo quality. Additionally, the review summarizes challenges in the translation of optical imaging systems into routine clinical practice, providing recommendations for their future development. Finally, we identify suitable imaging approaches for interrogating the mechanisms underpinning successful embryo development.

Characterization of individual spores of two biological insecticides, Bacillus thuringiensis and Lysinibacillus sphaericus, in response to glutaraldehyde using single-cell optical approaches.

Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus (Ls) are the most widely used microbial insecticides. Both encounter unfavorable environmental factors and pesticides in the field. Here, the responses of Bt and Ls spores to glutaraldehyde were characterized using Raman spectroscopy and differential interference contrast imaging at the single-cell level. Bt spores were more sensitive to glutaraldehyde than Ls spores under prolonged exposure: <1.0% of Bt spores were viable after 10min of 0.5% (v/v) glutaraldehyde treatment, compared to ~ 20% of Ls spores. The Raman spectra of glutaraldehyde-treated Bt and Ls spores were almost identical to those of untreated spores; however, the germination process of individual spores was significantly altered. The time to onset of germination, the period of rapid Ca2+-2,6-pyridinedicarboxylic acid (CaDPA) release, and the period of cortex hydrolysis of treated Bt spores were significantly longer than those of untreated spores, with dodecylamine germination being particularly affected. Similarly, the germination of treated Ls spores was significantly prolonged, although the prolongation was less than that of Bt spores. Although the interiors of Bt and Ls spores were undamaged and CaDPA did not leak, proteins and structures involved in spore germination could be severely damaged, resulting in slower and significantly prolonged germination. This study provides insights into the impact of glutaraldehyde on bacterial spores at the single cell level and the variability in spore response to glutaraldehyde across species and populations.

Photonic-electronic integrated circuit-based coherent LiDAR engine

Chip-scale integration is a key enabler for the deployment of photonic technologies. Coherent laser ranging or FMCW LiDAR, a perception technology that benefits from instantaneous velocity and distance detection, eye-safe operation, long-range, and immunity to interference. However, wafer-scale integration of these systems has been challenged by stringent requirements on laser coherence, frequency agility, and the necessity for optical amplifiers. Here, we demonstrate a photonic-electronic LiDAR source composed of a micro-electronic-based high-voltage arbitrary waveform generator, a hybrid photonic circuit-based tunable Vernier laser with piezoelectric actuators, and an erbium-doped waveguide amplifier. Importantly, all systems are realized in a wafer-scale manufacturing-compatible process comprising III-V semiconductors, silicon nitride photonic integrated circuits, and 130-nm SiGe bipolar complementary metal-oxide-semiconductor (CMOS) technology. We conducted ranging experiments at a 10-meter distance with a precision level of 10 cm and a 50 kHz acquisition rate. The laser source is turnkey and linearization-free, and it can be seamlessly integrated with existing focal plane and optical phased array LiDAR approaches.

Wave optical model for tomographic volumetric additive manufacturing

Tomographic Volumetric Additive Manufacturing (TVAM) allows printing of mesoscopic objects within seconds or minutes. In TVAM, tomographic patterns are illuminated onto a rotating glass vial which contains a photosensitive resin. Current pattern optimization is based on a ray optical assumption which ultimately leads to limited resolution around 20 µm and varying throughout the volume of the 3D object. In this work, we introduce a rigorous wave-based optical amplitude optimization scheme for TVAM which shows that high-resolution printing is theoretically possible over the full volume. The wave optical optimization approach is based on an efficient angular spectrum method of plane waves with custom written memory efficient gradients and allows for optimization of realistic volumes for TVAM such as (100μm)3 or (10 mm)3 with 5503 voxels and 600 angles. Our simulations show that ray-optics start to produce artifacts when the desired features are 20 µm and below and more importantly, the amplitude modulated TVAM can reach sub 20 µm features when optimizing the patterns using a full wave model.

Evaluation of calibrated and uncalibrated optical imaging approaches for relative cerebral oxygen metabolism measurements in awake mice

Objective. The continuous delivery of oxygen is critical to sustain brain function, and therefore, measuring brain oxygen consumption can provide vital physiological insight. In this work, we examine the impact of calibration and cerebral blood flow (CBF) measurements on the computation of the relative changes in the cerebral metabolic rate of oxygen consumption (rCMRO2) from hemoglobin-sensitive intrinsic optical imaging data. Using these data, we calculate rCMRO2, and calibrate the model using an isometabolic stimulus. Approach. We used awake head-fixed rodents to obtain hemoglobin-sensitive optical imaging data to test different calibrated and uncalibrated rCMRO2 models. Hypercapnia was used for calibration and whisker stimulation was used to test the impact of calibration. Main results. We found that typical uncalibrated models can provide reasonable estimates of rCMRO2 with differences as small as 7%–9% compared to their calibrated models. However, calibrated models showed lower variability and less dependence on baseline hemoglobin concentrations. Lastly, we found that supplying the model with measurements of CBF significantly reduced error and variability in rCMRO2 change calculations. Significance. The effect of calibration on rCMRO2 calculations remains understudied, and we systematically evaluated different rCMRO2 calculation scenarios that consider including different measurement combinations. This study provides a quantitative comparison of these scenarios to evaluate trade-offs that can be vital to the design of blood oxygenation sensitive imaging experiments for rCMRO2 calculation.

Birefringence mapping of biological tissues based on polarization sensitive non-interferometric quantitative phase imaging technique

ObjectiveOral cancer is a leading cause of mortality globally, particularly affecting developing regions where oral hygiene is often overlooked. The optical properties of tissues are vital for diagnostics, with polarization imaging emerging as a label-free, contrast-enhancing technique widely employed in medical and scientific research over past few decades. Materials and methodsWe present a novel polarization sensitive quantitative phase imaging of biological tissues by incorporating the conventional polarization microscope and transport of intensity equation-based phase retrieval algorithm. This integration provides access to the birefringence mapping of biological tissues. The inherent optical anisotropy in biological tissues induces the polarization dependent refractive index variations which can provide the detailed insights into the birefringence characteristics of their extracellular constituents. Experimental investigations were conducted on both normal and cancerous oral tissue samples by recording a set of three polarization intensity images for each case with a step size of 2 μm. ResultsA noteworthy increment in birefringence quantification was observed in cancerous as compared to the normal tissues, attributed to the proliferation of abnormal cells during cancer progression.The mean birefringence values were calculated for both normal and cancerous tissues, revealing a significant increase in birefringence of cancerous tissues (2.1 ± 0.2) × 10−2 compared to normal tissues (0.8 ± 0.2) × 10−2. Data were collected from 8 patients in each group under identical experimental conditions. ConclusionThis polarization sensitive non-interferometric optical approach demonstrated effective discrimination between cancerous and normal tissues, with various parameters indicating elevated values in cancerous tissues.

Experimental saturation characteristics of the PMT and adaptive compensation algorithm for OWC

Orthogonal frequency division multiplexing (OFDM) utilizes numerous sub-carriers to achieve high transmission data rates. The frequency selectivity of the channel becomes a crucial factor influencing the communication performance of OFDM-based systems. In optical wireless communication (OWC) systems, the photomultiplier tube (PMT) may experience saturation when the incident optical power approaches its saturation threshold. This paper, for the first time, characterizes the saturation levels of a high-speed PMT based on the measured amplitude in the time domain and the output response of the PMT in the frequency domain. Additionally, an adaptive optical saturation compensation algorithm, leveraging an electronically controlled variable optical attenuator, is proposed to realize a reliable OWC system. Experimental results demonstrate that the proposed saturation compensation method achieves a higher tolerance to large dynamic signal and background radiation compared with that without compensation, while maintaining a satisfactory bit error rate.

High-fidelity 3D reconstruction of plants using Neural Radiance Fields

Accurate reconstruction of plant phenotypes plays a key role in optimizing sustainable farming practices in the field of Precision Agriculture (PA). Currently, optical sensor-based approaches dominate the field, but the need for high-fidelity 3D reconstruction of crops and plants in unstructured agricultural environments remains challenging. Recently, a promising development has emerged in the form of Neural Radiance Fields (NeRF), a novel method that utilizes neural density fields. This technology has shown impressive performance in various novel vision synthesis tasks, but has remained relatively unexplored in the agricultural context. In our study, we focus on two fundamental tasks within plant phenotyping: (1) the synthesis of 2D novel-view images and (2) the 3D reconstruction of crop and plant models. We explore the world of NeRF, in particular two state-of-the-art (SOTA) methods: Instant-NGP, which excels in generating high-quality images with impressive training and inference speed, and Instant-NSR, which improves the reconstructed geometry by incorporating the Signed Distance Function (SDF) during training. In particular, we present a novel plant phenotype dataset comprising real plant images from production environments. This dataset is a first-of-its-kind initiative aimed at comprehensively exploring the advantages and limitations of NeRF in agricultural contexts. Our experimental results show that NeRF demonstrates commendable performance in the synthesis of novel-view images and is able to achieve reconstruction results that are competitive with Reality Capture, a leading commercial software for 3D Multi-View Stereo (MVS)-based reconstruction. Moreover, our study also highlights certain drawbacks of NeRF, including relatively slow training speeds, performance limitations in cases of insufficient sampling, and challenges in obtaining geometry quality in complex setups. In conclusion, NeRF introduces a new paradigm in plant phenotyping, providing a powerful tool capable of generating multiple representations, such as multi-view images, point cloud and mesh, from a single process.

Inside-out: Synergising leaf biochemical traits with stomatal-regulated water fluxes to enhance transpiration modelling during abiotic stress.

As the global climate continues to change, plants will increasingly experience abiotic stress(es). Stomata on leaf surfaces are the gatekeepers to plant interiors, regulating gaseous exchanges that are crucial for both photosynthesis and outward water release. To optimise future crop productivity, accurate modelling of how stomata govern plant-environment interactions will be crucial. Here, we synergise optical and thermal imaging data to improve modelled transpiration estimates during water and/or nutrient stress (where leaf N is reduced). By utilising hyperspectral data and partial least squares regression analysis of six plant traits and fluxes in wheat (Triticum aestivum), we develop a new spectral vegetation index; the Combined Nitrogen and Drought Index (CNDI), which can be used to detect both water stress and/or nitrogen deficiency. Upon full stomatal closure during drought, CNDI shows a strong relationship with leaf water content (r2 = 0.70), with confounding changes in leaf biochemistry. By incorporating CNDI transformed with a sigmoid function into thermal-based transpiration modelling, we have increased the accuracy of modelling water fluxes during abiotic stress. These findings demonstrate the potential of using combined optical and thermal remote sensing-based modelling approaches to dynamically model water fluxes to improve both agricultural water usage and yields.

Optical Imaging Method of Synthetic-Aperture Radar for Moving Targets

Traditional synthetic-aperture radar (SAR) imaging, while adept at capturing stationary scenes with clarity, often results in the blurring of moving targets due to Doppler spectrum disparities. To overcome this, this study introduces an innovative optical approach for imaging moving targets. By employing a spatial light modulator (SLM), the phase information of SAR data can be modulated onto a light beam. Then, the light propagation path is meticulously designed to take advantage of the free propagation of light to compensate for the phase differences in SAR data, thereby achieving focal clarity. Simulations and experimental validations have demonstrated that this method surpasses traditional digital imaging techniques in terms of focusing precision. Additionally, the processing delay is only as long as the time taken for light propagation. The optical path is simple, avoiding complex assembly and alignment. This novel approach opens up new possibilities for the SAR imaging of moving targets, offering potential applications in moving target extraction, separation, and velocity estimation.

Demonstration of computer vision for void characterisation of 3D-printed continuous carbon fibre composites

Microstructural void formation during the processing of continuous fibre-reinforced polymer composites are a significant limitation of processes such as 3D printing, as voids inhibit resultant mechanical properties. Traditional optical microscopy approaches to void characterisation are tedious and are prone to errors due to non-ideal but realistic image conditions, including low contrast typical of microscopic images. This paper proposes a novel application of automated computer vision image processing techniques (i.e. a contrast-limited adaptive histogram equalisation (CLAHE) algorithm and Otsu's method) for detailed void characterisation of continuous fibre-reinforced composites. Microstructural void fraction was determined for both unidirectional and bi-axial laminates of a variety of thicknesses. The void characterisation by computer vision was shown to produce comparable results with manual contrast/brightness control, but with significantly less standard deviation. The computer vision software used in void characterisation is made freely available online at https://github.com/Xiao-ying/VoidDetector.

Flexible and Fully Printed Passive RF Resonators for Contact‐Less Solution Sensing

AbstractIn recent years, several efforts have been dedicated to the development of portable and versatile microwave technologies for contact‐less liquid sensing and characterization. With respect to existing electrochemical and optical approaches, microwave liquid sensors enable high‐sensitivity and label‐free sensing with increased operation stability and robustness, and in relatively simple and inexpensive device formats. Nonetheless, current microwave solution sensing systems are still limited by either their reliance on wired connections to external electronics or by their widespread implementation on conventional rigid substrates. These limitations hinder the seamless integration of such sensors within conventional (micro)fluidic systems for real‐time solution monitoring, particularly when near‐field coupling between the sensors and the liquid under test needs to be established for operation. By leveraging the versatile material deposition capabilities granted by solution‐phase processing, a fully printed and mechanically flexible microwave resonator design is introduced that allows untethered solution sensing whether immersed in or in proximity to the liquid under test. The mechanical properties of this device facilitate the noninvasive/nondestructive integration of the device on commercial tubing. These characteristics, along with its cost‐effectiveness and its ease of fabrication, favor the seamless integration of this device into fluidic and microfluidic systems, for real‐life applications.