Illumination Light Research Articles

Review of development for ptychography algorithm

With the development of synchrotron radiation technology and the improvement of light source coherence, ptychography has developed rapidly. Ptychography algorithm solves the problems of slow convergence and easily falls into the local optimal solution and stagnation of the traditional coherent diffraction imaging algorithm. It has the advantages of large imaging field of view, robustness of algorithm, high tolerance to error and wide range of applications, and is becoming a hot research direction in the field of coherent diffraction imaging. Ptychography reconstructs the complex amplitude distribution and illumination light of the sample by iterative algorithms, which can theoretically reach the resolution of the diffraction limit. It has excellent applications in the fields of wavefront detection, phase imaging and optical metrology. This paper first introduces the background of the proposed ptychography algorithm and briefly describes the problem of coherent diffraction imaging algorithm and its development, and then summarizes the development of ptychography algorithm in detail, mainly including the mainstream algorithm of ptychography and its kernel. This paper then describes in detail the improvement of algorithms corresponding to the improvement of the efficiency of ptychography experiments, correction of position errors and the effect of illumination light multi-modal, and elaborates the algorithm flow. After analyzing the possible intersection of diffraction imaging and neural networks in the field of artificial intelligence, this paper introduces new algorithms with combining ptychography with artificial intelligence. New algorithms with combining ptychography with neural networks will have new potential applications in generality, accuracy and robustness. Finally, a specific parallelization implementation of the ptychography algorithm and common software packages are presented. The logic for writing the parallelization of the algorithm implementation of each package and the corresponding advantages and disadvantages of the packages are described in detail. The characteristics and performance of each package are then listed for reference. This paper helps to establish a global perspective of the algorithm itself, artificial intelligence and computational methods in the field of ptychography, and presents an important reference for systematically developing the ptychography method.

A novel single-step anodization approach for pani-doping oxide surfaces to improve the photocatalytic activity of titanium implants

Crystalline titanium oxides have shown photocatalytic activity (PCA) and the formation of antibacterial reactive oxygen species (ROS) when stimulated with UV light. Polyaniline (PANI) is a conductive polymer that has shown antibacterial effects. Previously, titanium oxides have been PANI-doped using a multi-step approach. In the present study, we compared PANI-doped specimens produced with a two-step method (ACV), to PANI-doped specimens produced by a novel single-step direct anodization (AAn) method, and a control group of anodized un-doped specimens. The surface morphology, oxide crystallinity, surface elemental composition, surface roughness, surface wettability, oxide adhesion, corrosion resistance, PCA, and ROS generation of each oxide group were evaluated. All groups exhibited mixed anatase and rutile phase oxides. The AAn group revealed less anatase and rutile, but more PANI-surface coverage. The AAn group exhibited significantly increased PCA after 60 min of direct UVA illumination compared to the ACV group, despite containing lower amounts of anatase and rutile. The ACV and AAn groups showed significant increases in ROS production after 4 h UVA illumination while the control group showed similar ROS production. These findings suggested that PANI doping using the novel direct anodization technique significantly improved PCA even for oxides containing less crystallinity. The S. aureus attachment response to each oxide group was also compared under UVA pre-illumination, UVA direct illumination, and no illumination (dark) lighting conditions. Although no significant differences were shown in the bacterial response, both PANI-doped groups exhibited less average bacterial attachment compared to the control group. The response of MC3T3-E1 pre-osteoblast cells to each oxide group was evaluated using MTT and live/dead assays, and no evidence of cytotoxicity was found. Since many, if not most, titanium implant devices are routinely anodized as a part of the manufacturing processes, these study findings are applicable to a wide variety of implant applications.

Nanoflower-like P-doped Nickel Oxide as a Catalytic Counter Electrode for Dye-Sensitized Solar Cells.

Flower-like phosphorus-doped nickel oxide (P-NiO) is proposed as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The flower-like nickel oxide essentially serves as the matrix for the CE, which is expected to promote a two-dimensional electron transport pathway. The phosphorus is intended to improve the catalytic ability by creating more active sites in the NiO for the catalysis of triiodide ions (I3-) to iodide ions (I-) on the surface of the CE. The P-NiO is controlled by a sequencing of precursor concentration, which allows the P-NiO to possess different features. The debris aggregation occurs in the P-NiO-1, while the P-NiO-0.75 leads to the incomplete flower-like nanosheets. The complete flower-like morphology can be observed in the P-NiO-0.5, P-NiO-0.25 and P-NiO-0.1 catalytic electrodes. The DSSC with the P-NiO-0.5 CE achieves a power conversion efficiency (η) of 9.05%, which is better than that of the DSSC using a Pt CE (η = 8.51%); it also performs better than that with the Pt CE, even under rear illumination and dim light conditions. The results indicate the promising potential of the P-NiO CE to replace the expensive Pt CE.

Modelling the Public Perception of Urban Public Space Lighting Based on SDGSAT-1 Glimmer Imagery: A Case Study in Beijing, China

Public space lighting is important for public perception, human health and urban planning. Previous studies used nighttime light remote sensing data to evaluate light pollution and its impacts on human health, few investigated the impact on public perception. This study combines Beijing’s SDGSAT-1 imagery with ground-measured and public perception data to evaluate the feasibility of SDGSAT-1 images simulating public perception. First, ground measurements were performed to collect light attributes and questionnaires were distributed to assess public safety and comfort. Next, the relationship between SDGSAT-1 image and measured illuminance was established. Lastly, public perception in Beijing was estimated. The results show that, (1) public perception is affected by panoramic illuminance, uniformity, and blue light; (2) although illuminance is positively related to public perception, it shows diminishing marginal returns; (3) a strong correlation is found between panoramic illuminance and SDGSAT-1 image; (4) the perception map shows that most areas in Beijing can provide safe and comfortable lighting, while there are also insufficient or overlit in some places. This study explores methods for assessing public perceptions by satellite data, indicates remote sensing can provide a larger-scale and quantitative evaluation of public perception, which can contribute to urban lighting design and sustainable development.

External Illumination Enables Coaxial Sensing of Surface and Subsurface Molten Pool Geometry in LPBF

Laser powder bed fusion (LPBF) attracts the attention of high-end manufacturing sectors for its capability of depositing free-form components with elevated mechanical properties. However, due to the intrinsic nature of the feedstock material and the interaction with the laser beam, the process is prone to defect formation and manufacturing inaccuracies. Therefore, the development of a monitoring architecture capable of measuring the geometrical features of the process tool (i.e., the melt pool generated by the laser-material interaction) is of paramount importance. This information may then be exploited to evaluate process stability. In this work, a high-speed camera was implemented coaxially in the optical chain of an LPBF system to extrapolate the geometrical features of the molten pool surface and its oscillatory behaviour, with elevated spatial and temporal resolution. A secondary light source was tested in both coaxial and off-axis configuration to dominate process emission and assess optimal illumination conditions for extracting the molten pool’s geometrical features. Preliminary results showed that the off-axis configuration of the illumination light enabled direct measurement of the molten pool surface geometry. A newly developed image processing algorithm based on illuminated images obtained via the coaxial observation frame was employed to provide automated identification of the melt pool geometry. Moreover, bright reflections of the external illumination over the melt surface could be clearly observed and used to characterise the oscillatory motion of the molten material. This information may therefore be taken as an indirect indicator of the molten pool penetration depth, hence providing information regarding the subsurface geometry. A successive experimental investigation showed the capability of the monitoring architecture to resolve the molten pool’s length, width and area with elevated acquisition frequency. Molten pool surface oscillations in the kHz range could be correlated to the penetration depth while the molten pool width measured via the high-speed imaging setup corresponded to the track width of the depositions. Hence, the methodological approach for the concurrent measurement of the molten pool’s geometry in three spatial dimensions was demonstrated and may be used to track the stability of LPBF depositions.

Extended depth-of-field light-sheet microscopy improves imaging of large volumes at high numerical aperture.

Light-sheet microscopes must compromise among field of view, optical sectioning, resolution, and detection efficiency. High-numerical-aperture (NA) detection objective lenses provide higher resolution, but their narrow depth of field inefficiently captures the fluorescence signal generated throughout the thickness of the illumination light sheet when imaging large volumes. Here, we present ExD-SPIM (extended depth-of-field selective-plane illumination microscopy), an improved light-sheet microscopy strategy that solves this limitation by extending the depth of field (DOF) of high-NA detection objectives to match the thickness of the illumination light sheet. This extension of the DOF uses a phase mask to axially stretch the point-spread function of the objective lens while largely preserving lateral resolution. This matching of the detection DOF to the illumination-sheet thickness increases the total fluorescence collection, reduces the background, and improves the overall signal-to-noise ratio (SNR), as shown by numerical simulations, imaging of bead phantoms, and imaging living animals. In comparison to conventional light sheet imaging with low-NA detection that yields equivalent DOF, the results show that ExD-SPIM increases the SNR by more than threefold and dramatically reduces the rate of photobleaching. Compared to conventional high-NA detection, ExD-SPIM improves the signal sensitivity and volumetric coverage of whole-brain activity imaging, increasing the number of detected neurons by over a third.

Effect of Grating Ruling Machine System Errors on Grating Spectral Performance

Grating groove functions scalar theory can describe the light source through the grating interference and diffraction effect of the physical phenomenon of splitting light. It can be used to represent the distribution of the complex amplitude of the illumination light source on the diffraction screen under the action of the diffraction grating and display the information on the diffracted light position and intensity distribution. As a result, the effect of groove error on the intensity of grating ghost lines and stray light is analyzed. This paper presents an energy solution and analysis of the grating periodic groove error utilizing the grating scalar diffraction theory. Based on this, the effect of the core components of the grating ruling machines, such as screw and worm gear, on the stray light and ghost line of the grating is analyzed. Finally, the random groove error is analyzed. The analysis results show that the worm gear error is an important reason for the appearance of ghost lines in the machine ruling grating, and the lead screw error and random grooving error are the main reasons for the stray light produced by the grating. We optimize the worm gear, lead screw, and error compensation system of the grating ruling machine to effectively improve the ruling quality of the grating.

Polarization Descattering Imaging of Underwater Complex Targets Based on Mueller Matrix Decomposition

The traditional polarization imaging techniques cannot obtain the polarization characteristics with global variation, and the reconstruction of the target with different optical properties concurrently is seriously distorted. In this work, we overcome the aforementioned shortcomings by using the polar decomposition method to estimate the Mueller matrix of the target in the full field of view. Simultaneously, the illumination light with globally varying polarization state is calculated to suppress the noise caused by computational imaging. The descattering imaging experiments through turbid water indicate that the images recovered by our method present the similarity to the targets without scattering, and the noise is suppressed to some extent. Further, we prove the superiority of the proposed method by comparing with other polarization underwater imaging strategies.

Interactive VPL-based global illumination on the GPU using fuzzy clustering

Physically-based synthesis of high quality imagery, including global illumination light transport phenomena, results in a significant workload, which makes interactive rendering a very challenging task. We propose a VPL-based ray tracing approach that runs entirely in the GPU and achieves interactive frame rates while handling global illumination light transport phenomena. This approach is based on clustering both shading points and VPLs and computing visibility only among clusters’ representatives. A new massively parallel K-means clustering algorithm, enables efficient execution in the GPU. Rendering artifacts, that could result from the piecewise constant approximation of the VPLs/shading points visibility function introduced by the clustering, are smoothed away by resorting to an innovative approach based on fuzzy clustering and weighted interpolation of the visibility function. The effectiveness of the proposed approach is experimentally verified for a collection of scenes, with frame rates larger than 3 fps and up to 25 fps being demonstrated.

Context-Aware Complex Human Activity Recognition Using Hybrid Deep Learning Models

Smart devices, such as smartphones, smartwatches, etc., are examples of promising platforms for automatic recognition of human activities. However, it is difficult to accurately monitor complex human activities on these platforms due to interclass pattern similarities, which occur when different human activities exhibit similar signal patterns or characteristics. Current smartphone-based recognition systems depend on traditional sensors, such as accelerometers and gyroscopes, which are built-in in these devices. Therefore, apart from using information from the traditional sensors, these systems lack the contextual information to support automatic activity recognition. In this article, we explore environmental contexts, such as illumination (light conditions) and noise level, to support sensory data obtained from the traditional sensors using a hybrid of Convolutional Neural Network and Long Short-Term Memory (CNN–LSTM) learning models. The models performed sensor fusion by augmenting low-level sensor signals with rich contextual data to improve the models’ recognition accuracy and generalization. Two sets of experiments were performed to validate the proposed solution. The first set of experiments used triaxial inertial sensing signals to train baseline models, while the second set of experiments combined the inertial signals with contextual information from environmental sensors. The obtained results demonstrate that contextual information, such as environmental noise level and light conditions using hybrid deep learning models, achieved better recognition accuracy than the traditional baseline activity recognition models without contextual information.

Deep semantic segmentation for the quantification of grape foliar diseases in the vineyard.

Plant disease evaluation is crucial to pathogen management and plant breeding. Human field scouting has been widely used to monitor disease progress and provide qualitative and quantitative evaluation, which is costly, laborious, subjective, and often imprecise. To improve disease evaluation accuracy, throughput, and objectiveness, an image-based approach with a deep learning-based analysis pipeline was developed to calculate infection severity of grape foliar diseases. The image-based approach used a ground imaging system for field data acquisition, consisting of a custom stereo camera with strobe light for consistent illumination and real time kinematic (RTK) GPS for accurate localization. The deep learning-based pipeline used the hierarchical multiscale attention semantic segmentation (HMASS) model for disease infection segmentation, color filtering for grapevine canopy segmentation, and depth and location information for effective region masking. The resultant infection, canopy, and effective region masks were used to calculate the severity rate of disease infections in an image sequence collected in a given unit (e.g., grapevine panel). Fungicide trials for grape downy mildew (DM) and powdery mildew (PM) were used as case studies to evaluate the developed approach and pipeline. Experimental results showed that the HMASS model achieved acceptable to good segmentation accuracy of DM (mIoU > 0.84) and PM (mIoU > 0.74) infections in testing images, demonstrating the model capability for symptomatic disease segmentation. With the consistent image quality and multimodal metadata provided by the imaging system, the color filter and overlapping region removal could accurately and reliably segment grapevine canopies and identify repeatedly imaged regions between consecutive image frames, leading to critical information for infection severity calculation. Image-derived severity rates were highly correlated (r > 0.95) with human-assessed values, and had comparable statistical power in differentiating fungicide treatment efficacy in both case studies. Therefore, the developed approach and pipeline can be used as an effective and efficient tool to quantify the severity of foliar disease infections, enabling objective, high-throughput disease evaluation for fungicide trial evaluation, genetic mapping, and breeding programs.

Effects of illuminance intensity on the green channel of remote photoplethysmography (rPPG) signals.

Point-of-care remote photoplethysmography (rPPG) devices that utilize low-cost RGB cameras have drawn considerable attention due to their convenience in contactless and non-invasive vital signs monitoring. In rPPG, sufficient lighting conditions are essential for obtaining accurate diagnostics by observing the complete signal morphology. The effects of illuminance intensity and light source settings play a significant role in rPPG assessment quality, and it was previously observed that different lighting schemes result in different signal quality and morphology. This study presents a quantitative empirical analysis where the quality and morphology of rPPG signals were assessed under different light settings. Participants' faces were exposed to the white LED spotlight, first when the sources were installed directly behind the video camera, and then when the sources were installed in a cross-polarized scheme. Hence, the effect of specular reflectance on rPPG signals could be observed in an increasing projection. The signal qualities were analyzed in each intensity level using a signal-to-noise (SNR) ratio metric. In 3 of 7 participants, placing the video camera on the same level as the light source led to signal quality loss of up to 3 dB for the range 30-60 Lux. In addition, two fundamental morphological features were analyzed, and the derivative-related feature was found to be increasing with illuminance intensity in 6 of 7 participants.

Chip-based wide field-of-view total internal reflection fluorescence microscopy.

Conventional total internal reflection fluorescence (TIRF) microscopy requires either an oil-immersed objective with high numerical aperture or a bulky prism with high refractive index to generate the evanescent waves that work as the illumination source for fluorophores. Precise alignment of the optical path is necessary for optimizing the imaging performance of TIRF microscopy, which increases the operation complexity. In this Letter, a planar photonic chip composed of a dielectric multilayer and a scattering layer is proposed to replace the TIRF objective or the prism. The uniform evanescent waves can be excited under uncollimated incidence through this chip, which simplifies the alignment of the optical configurations and provides shadowless illumination. Due to the separation of the illumination and detection light paths, TIRF microscopy can have a large field-of-view (FOV).

Novel light delivery method for performing transbronchial photodynamic therapy ablation to treat peripheral lung cancer: A pilot study

BackgroundPhotodynamic therapy involves using a photosensitizer with l illumination and is recommended for treating early, centrally located lung cancers, but it is not a standard treatment for peripheral lung tumor.. We previously proposed a novel light delivery method, in which lipiodol is perfused into the bronchial tree to increase the scope of illumination via the fiber effect. Herein, we attempted this novel technique under electromagnetic bronchoscope guidance in a hybrid operation room where lipiodol facilitated light diffusion, and evaluated the effectiveness and feasibility of this technique for peripheral lung cancers. MethodsThis phase 0 pilot study included three patients with peripheral lung cancers (primary tumors ≤20-mm diameter). The photodynamic therapy was administered using Porfimer sodium as the photosensitizer, and an electromagnetic navigation bronchoscope in a hybrid operating room to guide the catheter to the tumor. This facilitated lipiodol infusion to encase the tumor and permit the transbronchial photodynamic therapy ablation. ResultsAdministering 630 nm 200 J/cm (400mW/500sec) energy through a 3-cm cylindrical diffusing laser fiber was safe; no significant acute complications were observed. Although the treatment outcome was unsatisfactory due to the low light dose, tumor pathology in one case revealed tumor necrosis, with no significant damage to the surrounding lung tissue. ConclusionsNovel light delivery transbronchial photodynamic therapy ablation for peripheral lung tumors is feasible and safe. Additional clinical trials may help determine the best illumination plan and light dose through multiple deliveries from multiple angles.

High-Efficiency Continuous-Luminescence-Controllable Performance and Antithermal Quenching in Bi3+-Activated Phosphors.

Recently, Bi3+-activated phosphors have been widely researched for phosphor-converted light-emitting diode (pc-LED) applications. Herein, novel full-spectrum A3BO7:Bi3+ (A = Gd, La; B = Sb, Nb) phosphors with a luminescence-tunable performance were achieved by a chemical substitution strategy. In the La3SbO7 host material, a new luminescent center was introduced, with Gd3+ replacing La3+. The photoluminescence (PL) spectra show a large blue shift from 520 to 445 nm, thus achieving regulation from green to blue lights. Moreover, a series of solid solution-phase phosphors La3Sb1-xNbxO7:Bi3+ were prepared by replacing Sb with Nb, and a PL spectral tunability from green (520 nm) to orange-red (592 nm) was realized. Temperature-dependent PL spectra show that La3-xGdxSbO7:Bi3+ phosphors have excellent thermal stability. Upon 350 nm excitation, the PL intensity of La3-xGdxSbO7:Bi3+ phosphors at 150 °C remained at more than 93% at room temperature. With Gd3+ doping, the thermal stability gradually improved, and LaGd2SbO7:0.03Bi3+ represents splendid antithermal quenching (135.2% at 150 °C). Finally, a full-visible spectrum for pc-LED with a high color-rendering index (Ra = 94.4) was obtained. These results indicated that chemical substitution is an effective strategy to adjust the PL of Bi3+, which is of great significance in white-light illumination and accurate plant lighting.

Frontispiece: Emerging Trends in Fluorescence Bioimaging of Divalent Metal Cations Using Small‐Molecule Indicators

Three new trends in fluorescence bioimaging of divalent metal cations using small-molecule indicators have been highlighted in this concept article by Liu, Zhang and Chen on page 17ff: Red-shifted indicators dwelling in the under-used far-red and NIR channels for multiplexed imaging; hybrid indicators combining the superior optical properties of synthetic dyes and the targetability of proteins; and biocompatible indicators under strong illumination lights in long term recording. These trends fall in line with the new initiative of “4D cellular physiology” which marked a grand vision of biological research in the era of big data.

High-performance lensless diffraction imaging from diverse holograms by three-dimensional scanning.

For lensless diffraction imaging, it is a challenging dilemma to achieve a large field of view (FOV) and high resolution with a small amount of data at the same time. Ptychography can reconstruct the high-resolution image and illumination light simultaneously. But the illumination is limited to a small size by a probe in typical ptychography. For large samples, it takes much time to collect abundant patterns and has strict requirements for the computing power of computers. Another widely applied method, multi-height measurement, can realize a wide FOV with several holograms. But, the recovered image is easily destroyed by the background noise. In this Letter, a lensless diffraction imaging method by three-dimensional scanning is proposed. All positions of the object are different in three directions instead of scanning schemes only on a plane or along the optic axis, so more diversity of diffraction information is obtained. We apply the illumination without the limit of a confined aperture, which means that the imaging FOV of a pattern is equal to the size of the utilized image sensor. In comparison with the multi-height method, our method can separate the illumination background noise from the retrieved object. Consequently, the proposed method realized high resolution and contrast, large FOV, and the removal of background noise simultaneously. Experimental validations and comparisons with other methods are presented.

Two-dimensional measurement of resonance in MEMS resonators using stroboscopic differential interference contrast microscopy.

We report the two-dimensional (2D) measurement of resonance in MEMS resonators using stroboscopic differential interference contrast (DIC) microscopy, for the investigation of the linear and nonlinear oscillations of MEMS resonators. The DIC microscopy measures the interference of two sheared illumination light beams reflected from the sample surface to determine the differential surface deflection. By modulating the illumination light at the resonance frequency, the DIC image of the MEMS resonator periodically change its brightness and contrast with the sweeping illumination phase, which have been used to derive the oscillation amplitude and the resonance mode shape of the MEMS resonator. Comparing with conventional interference microscopy, the DIC microscopy can observe the surface deflection larger than the wavelength of the illumination light, enabling the measurement of nonlinear oscillations with a large oscillation amplitude. We demonstrate that the stroboscopic DIC microscopy can measure the 2D mechanical resonance with a high vertical resolution at the nanometer(nm)-scale, and a large measurement range of ∼1µm, which is very promising for the investigation of linear and nonlinear oscillations of MEMS resonators.

Far-Field and Non-Intrusive Optical Mapping of Nanoscale Structures.

Far-field high-density optics storage and readout involve the interaction of a sub-100 nm beam profile laser to store and retrieve data with nanostructure media. Hence, understanding the light–matter interaction responding in the far-field in such a small scale is essential for effective optical information processing. We present a theoretical analysis and an experimental study for far-field and non-intrusive optical mapping of nanostructures. By a comprehensive analytical derivation for interaction between the modulated light and the target in a confocal laser scanning microscopy (CLSM) configuration, it is found that the CLSM probes the local density of states (LDOSs) in the far field rather than the sample geometric morphology. With a radially polarized (RP) light for illumination, the far-field mapping of LDOS at the optical resolution down to 74 nm is obtained. In addition, it is experimentally verified that the target morphology is mapped only when the far-field mapping of LDOS coincides with the geometric morphology, while light may be blocked from entering the nanostructures medium with weak or missing LDOS, hence invalidating high-density optical information storage and retrieval. In this scenario, nanosphere gaps as small as 33 nm are clearly observed. We further discuss the characterization for far-field and non-intrusive interaction with nanostructures of different geometric morphology and compare them with those obtainable with the projection of near-field LDOS and scanning electronic microscopic results.

Self-oscillation and self-rotation of an optically-responsive liquid crystal elastomer pendulum

Liquid crystal elastomers (LCEs) have been widely used in active machinery, optical machinery, robotics, biological materials, medical and other fields, with advantage of good optical sensing performance. In this work, dynamics of a LCE-based optically-responsive pendulum system is theoretically investigated by proposing a nonlinear dynamic model. The self-oscillation and self-rotation can be triggered by steady illumination, in which the damping dissipation is compensated by the energy input from environment illumination to maintain the periodic motion. With theoretical modeling and numerical calculation, three typical motion regimes of the LCE pendulum are found, namely, static regime, self-oscillation regime and self-rotation regime. For different physical parameters, the critical conditions to excite the three motion regimes are given quantitatively. Results demonstrate that the motion regime, amplitude, and period of the LCE pendulum can be controlled by adjusting the illumination region, light intensity, damping coefficient, and gravitational acceleration. The proposed optically-responsive LCE pendulum can provide potential applications in research on sensing environment, energy harvesting and motion actuation of active machines, etc.