Multiple Illumination Research Articles

Reversible Photochemical Switching via Plasmonically Enhanced Upconversion Photoluminescence

AbstractPhotochromic molecule‐incorporated optical devices offer desirable properties for photocontrollable optical systems, including advanced optical data storage and super‐resolution imaging. However, these molecules require multiple illumination sources, such as UV and visible light, for reversible photochemical reactions, which restricts their potential for advanced application. This study reports an effective strategy for modulating photoisomerization via a single near‐infrared light source assisted by plasmonically enhanced photoswitchable upconversion photoluminescence (UCPL). The proposed quasi‐periodic metal nanostructures to facilitate the resonance modes in the broadband region enable the substitution of the detrimental high‐energy light source (i.e., UV light) with near‐infrared stimuli, which is associated with UCPL enhancement of over two orders with spectrum orthogonality. To validate this concept, the accelerated reversible‐photoisomerization kinetics is experimentally confirmed by three‐ and tenfold amplification of the PL intensities of the photochromic disulfonyldiarylethene derivatives. Further validation of the proposed strategy is performed using photodynamic imaging, which reveals accelerated photoisomerization, high photocyclization stability, and high spatial resolution.

Organic indoor light harvesters achieving recorded output power over 500% enhancement under thermal radiated illuminances

Organic photovoltaic (OPV) cells have found their potential applications in the harvest of indoor light photons. However, the output power of such indoor devices is usually far from the demand of the internet of things. Therefore, it is essential to boost the output power of indoor organic photovoltaics to a much higher level. As wildly deployed among industrial and civil luminous environments, thermal radiation-based indoor light sources are alternative candidates to supply the essential power of the off-grid electronics with a broad consecutive emission spectrum. In this work, we evaluated the photovoltaic performance of organic solar cells under indoor incandescent and halogen illuminations. Impressively, under such thermal radiations, an improvement over 500% of the output power density can be achieved in comparison with that under light-emitting diodes and fluorescent lamps, reaching a record high value of 279.1 μW cm−2 by the PM6:Y6-based device. The remarkable power output is originated from the extra near-infrared spectrum of indoor thermal lights, which restricts the effective area under 10 cm2 in achieving 1 mW output power. This work clarifies the feasibility of collecting photons radiated from indoor thermal light sources through OPV cells, and enlightens the further applications of indoor OPV cells under multiple illumination environments.

2-D PBR Localization Complying With Constraints Forced by Active Radar Measurements

A new algorithm for passive bistatic radar (PBR) localization is proposed via joint exploitation of multiple illuminators of opportunity and measurements gathered by a colocated active radar. Ad-hoc constraints within the localization process are bestowed accounting for both a priori information on the PBR receive antenna main-beam size and the uncertainty characterizing active radar data, i.e., the root mean square error (RMSE) of range/bearing measurements. Hence, the estimation task is cast as an elliptic positioning problem, according to the constrained least squares framework. The resulting non-convex optimization problem is globally solved providing a closed-form estimate in Cartesian coordinates. The performance of the proposed estimator, in terms of RMSE, exhibits sensible improvement with respect to counterparts. The proposed technique is also applied to the case of a dynamic scenario for a bi-sensor surveillance system, where the active rotating platform acquires measurements at each scanning period. The results show the localization performance improvement achieved when the system is complemented with a PBR staring in a specific search sector of interest.

Compact and Free-Floating Satellite MIMO SAR Formations

We discuss a coherent synthetic aperture radar (SAR) formation where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> identical sensors transmit at the same time, code, and frequency. This is a particular multiple-input–multiple-output (MIMO) configuration, where the transmitted waveforms interfere together, resulting in an illumination pattern that randomly changes in space and time. Similar to the single-input–multiple-output (SIMO) formations, the diversity provided by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> receiver phase centers can be used to mitigate this interference and reduce the pulse repetition frequency (PRF) for achieving large swath coverage. The good point, in the MIMO case, is that the signal-to-noise ratio (SNR) gain of the system increases, theoretically, with the square of the number of elements. However, residual spurious sidelobes may appear as ghosts of the multiple illuminators. In practice, the power gain is to be optimized, together with ambiguity rejection, sidelobes, and azimuth resolution. The actual performances achievable by these formations in terms of impulse response function (IRF), SNR, and sensitivity to the precise positioning of the sensors are discussed theoretically and based on simulations.

Vision based two-level hand tracking system for dynamic hand gestures in indoor environment

Object detection and tracking is one of the most challenging phases in any image processing application. The challenges that arise during hand gesture recognition are: hand shape variation, presence of multiple persons, illumination variation or occlusion with background. In this paper, a robust hand detector and tracker algorithm has been proposed which overcomes the above difficulties to a great extent. The proposed system first detects hand using a combination of color and motion information. Then, the hand is tracked using combination of feature based tracker modified KLT algorithm and a color-based tracker Camshift algorithm. New feature points have been added to our modified combination of feature and color based tracker. This prevents the loss of tracking as seen in traditional KLT algorithm. The experiments carried out using the proposed system shows that the system provides better results in comparison to the existing literatures on various challenging hand sequences.

Metastable quantum dot for photoelectric devices via flash-induced one-step sequential self-formation

The first metastable phase Ag, ZnS: α-In 2 S 3 QDs were synthesized by ultrafast light-material interaction. The multiple irradiation of millisecond flash pulses facilitated thermodynamic non-equilibrium superheating and quenching for metastable QD formation, as well as sequential self-formation of α-In 2 S 3 QD nucleation, Ag-doping and ZnS-passivation by photo-responsive ionic kinetics. Upon multiple illumination of flash pulses, the synthesis mechanism of Ag, ZnS: α-In 2 S 3 QD was experimentally proved by atomic-resolution transmission electron microscopy (AR-TEM), scanning TEM (STEM) and diverse spectral analysis. To verify the metastable phase QD formation by superheating/quenching in reaction solution, the localized surface plasmon (LSP) properties and instantaneous temperature increment were theoretically calculated using finite-difference time-domain (FDTD) method. Finally, optoelectronic performance and long-term stability of as-synthesized QDs were evaluated by demonstrating the broad wavelength metal-semiconductor-metal (MSM) photoelectric device. • The first ultrafast light-induced metastable quantum dots were synthesized by one-step sequential self-formation. • Upon multiple illumination of flash pulses, synthesis mechanism of Ag, ZnS: α-In2S3 QD was experimentally proved. • The localized surface plasmon properties were theoretically calculated using finite-difference time-domain method. • Optoelectronic performance and long-term stability of QDs were evaluated by demonstrating MSM photoelectric device.

Research Progress and Development Trend of the Multi-Illuminator-based Passive Radar

Given the functions and performance advantages of passive radar, this paper first reviews the research history of passive radar for more than 80 years and then examines the research progress of related key technologies, including reference signal reconstruction, multipath clutter suppression, target detection, target tracking, and passive radar imaging. On this basis, the latest research results of typical experimental systems of passive radar abroad (particularly in European countries) are presented in terms of system structures, technical parameters, and performance indices. Then this paper focuses on the Multi-Illuminator-based PAssive Radar (MIPAR) series of Wuhan University in China. The target detection results of MIPAR in different frequency bands (HF/VHF/UHF/L) are given, that show the application potential of the MIPAR system in long-range early warning and close-range high-precision monitoring. Finally, the development trends of passive radar, including the integration of multiple illuminators, system network configuration, and intelligent signal processing, are discussed.

Data-Driven Parameter Choice for Illumination Artifact Correction of Digital Images

We propose a new procedure for image illumination correction with data-driven parameter choice. This procedure aims at estimating the reflectance image from a corrupted version in which the corruption is due to pointwise multiplicative illumination artifact. The log -illumination artefact consists of “smooth” variations of the intensity which are modelled by a function lying in a finite dimensional space. Then a -y-correction is incorporated. The question of model selection is difficult to solve. We propose an entropy minimization criterion for the selection of both the approximating log -illumination space dimension and the -y-coefficient, so that no parameter tuning is needed. Several experiments are presented using this approach. A comparison to other methods illustrates the relevance of this approach.

Domain decomposition based on the spectral element method for frequency-domain computational elastodynamics

We propose a domain decomposition method based on the spectral element method (DDM-SEM) for elastic wave computation in frequency domain. It combines the high accuracy of the spectral element method and the high degree of parallelism of a domain decomposition technique, which makes this method suitable for accurate and efficient simulations of large scale problems in elastodynamics. In the DDM-SEM, the original large-scale problem is divided into a number of well designed subdomains. We use the spectral element method independently for each subdomain, and the neighboring subdomains are connected by a frequency-domain version of Riemann transmission condition (RTC) for elastic waves. For the proposed method, we can employ the non-conforming meshes and different interpolation orders in different subdomains to maximize the efficiency. By separating the internal and boundary unknowns of each subdomain, an efficient and naturally parallelizable block LDU direct solver is developed to solve the final system matrix. Numerical experiments verify its accuracy and efficiency, and show that the proposed DDM-SEM can be a promising numerical tool for accurately and effectively solving large and multi-scale problems of elastic waves. It is potentially valuable for the frequency domain seismic inversion where multiple source illuminations are required.

Multi-beam X-ray ptychography for high-throughput coherent diffraction imaging

X-ray ptychography is a rapidly developing coherent diffraction imaging technique that provides nanoscale resolution on extended field-of-view. However, the requirement of coherence and the scanning mechanism limit the throughput of ptychographic imaging. In this paper, we propose X-ray ptychography using multiple illuminations instead of single illumination in conventional ptychography. Multiple locations of the sample are simultaneously imaged by spatially separated X-ray beams, therefore, the obtained field-of-view in one scan can be enlarged by a factor equal to the number of illuminations. We have demonstrated this technique experimentally using two X-ray beams focused by a house-made Fresnel zone plate array. Two areas of the object and corresponding double illuminations were successfully reconstructed from diffraction patterns acquired in one scan, with image quality similar with those obtained by conventional single-beam ptychography in sequence. Multi-beam ptychography approach increases the imaging speed, providing an efficient way for high-resolution imaging of large extended specimens.

Multispectral Interlaced Sparse Sampling Photoacoustic Tomography.

Multispectral photoacoustic tomography (PAT) is capable of resolving tissue chromophore distribution based on spectral un-mixing. It works by identifying the absorption spectrum variations from a sequence of photoacoustic images acquired at multiple illumination wavelengths. Due to multispectral acquisition, this inevitably creates a large dataset. To cut down the data volume, sparse sampling methods that reduce the number of detectors have been developed. However, image reconstruction of sparse sampling PAT is challenging because of insufficient angular coverage. During spectral un-mixing, these inaccurate reconstructions will further amplify imaging artefacts and contaminate the results. To solve this problem, we present the interlaced sparse sampling (ISS) PAT, a method that involved: 1) a novel scanning-based image acquisition scheme in which the sparse detector array rotates while switching illumination wavelength, such that a dense angular coverage could be achieved by using only a few detectors; and 2) a corresponding image reconstruction algorithm that makes use of an anatomical prior image created from the ISS strategy to guide PAT image computation. Reconstructed from the signals acquired at different wavelengths (angles), this self-generated prior image fuses multispectral and angular information, and thus has rich anatomical features and minimum artefacts. A specialized iterative imaging model that effectively incorporates this anatomical prior image into the reconstruction process is also developed. Simulation, phantom, and in vivo animal experiments showed that even under 1/6 or 1/8 sparse sampling rate, our method achieved comparable image reconstruction and spectral un-mixing results to those obtained by conventional dense sampling method.

Numerical investigation of depth-sensitive diffuse reflectance and fluorescence measurements on murine subcutaneous tissue with growing solid tumors.

In most biomedical optical spectroscopy platforms, a fiber-probe consisting of single or multiple illumination and collection fibers was commonly used for the delivery of illuminating light and the collection of emitted light. Typically, the signals from all collection fibers were combined and then sampled to characterize tissue samples. Such simple averaged optical measurements may induce significant errors for in vivo tumor characterization, especially in longitudinal studies where the tumor size and location vary with tumor stages. In this study, we utilized the Monte Carlo technique to optimize the fiber-probe geometries of a spectroscopy platform to enable tumor-sensitive diffuse reflectance and fluorescence measurements on murine subcutaneous tissues with growing solid tumors that have different sizes and depths. Our data showed that depth-sensitive techniques offer improved sensitivity in tumor detection compared to the simple averaged approach in both reflectance and fluorescence measurements. Through the numerical studies, we optimized the source-detector distances, fiber diameters, and numerical apertures for sensitive measurement of small solid tumors with varying size and depth buried in murine subcutaneous tissues. Our study will advance the design of a fiber-probe in an optical spectroscopy system that can be used for longitudinal tumor metabolism and vasculature monitoring.

3D nanometrology of transparent objects by phase calibration of a basic bright-field microscope for multiple illumination apertures.

Optical retrieval of the structure of transparent objects at the nanoscale requires adapted techniques capable of probing their interaction with light. Here, we considered a method based on calibration of the defocusing with partially coherent illumination and explored its phase retrieval capability over a wide range of illumination angles. We imaged: (1) commercial dielectric nanospheres to assess the phase calibration when measured along the optical axis, (2) custom-made nano-steps micropatterned in a glass substrate to assess the phase calibration when measured along the transversal axis, and (3) human cancer cells deposited on a glass substrate to assess the results of the calibration on complex transparent 3-dimensional samples. We first verified the model prediction in the spatial frequency domain and subsequently obtained a consistent and linear phase-calibration for illumination numerical apertures ranging from 0.1 to 0.5. Finally, we studied the dependence of the phase retrieval of a complex nanostructured object on the illumination aperture.

Exact Geometrical-Optics Scattering by a Class of Metallic Wedges Under Multiple Plane-Wave Illumination

Exact Geometrical-Optics Scattering by a Class of Metallic Wedges Under Multiple Plane-Wave Illumination

Porphyrin-sensitized quasi-solid solar cells with MOF composited titania aerogel photoanodes

ZnTPP-COOH porphyrin-based quasi-solid dye-sensitized solar cells were fabricated with the following three different photoanode materials: Ni-MOF@titania aerogel composite, Cu-MOF@titania aerogel composite, and pure titania aerogel. Their photovoltaic performances were investigated through photocurrent–photovoltage (J–V) curve, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy, and transient measurements of photocurrent and photovoltage decay. Among the three cells, the enhancement of photocurrent is observed in cells containing Ni-MOF@titania aerogel photoanodes. As a result, the Ni-MOF@titania aerogel photoanode–based cell achieved the highest photocurrent density of 8.88 mA/cm2 and power conversion efficiency of 2.34%. This value is higher than that of the other two devices. Moreover, the EIS analysis is used to understand better the possible electron transfer behind the photocurrent boosting in Ni-MOF@titania aerogel photoanode–based cell. Low Rct value (44.1 Ω) and low τd value of the Ni-MOF@titania aerogel device are the key factors to improve the electron flow, the Warburg diffusion of electrolyte, as well as the regeneration process. These factors are attributed as the reason for their best performance among other devices. Based on the results obtained, the plausible mechanism for electron transfer is discussed using the energy level cascades of TiO2/MOF/porphyrin dye. The transient measurements indicated that the devices exhibited good reproducibility under multiple illuminations.

Multiple angle digital holography for the shape measurement of the unpainted tympanic membrane.

The shape of the tympanic membrane (TM) plays an important role in sound transmission through the ear for hearing. Previously we developed a high-speed holographic system employing a tunable wavelength laser for rapid TM shape measurement. However, the tunable laser illumination was not sufficient to measure the shape of the unpainted TM due to the semi-transparency of the TM and short exposure time of the camera. This paper presents a new multiple angle illumination technique that allows us to use a higher power single wavelength laser to perform shape measurements on the unpainted TM. Accuracy of the new method is demonstrated by a measure of a step gauge provided by the National Institute of Standards and Technology. We successfully applied the new shape measurement method on a fresh postmortem human TM without any paint.

Accurate colorimetric images using LEDs

It is well known that more than three or four spectral measurements are required for accurate measurement of color under arbitrary illumination. Previous work has shown 6 to 10 measurements can yield accurate results on average, but with significant numbers of errors above the threshold of obvious visual detection. We demonstrate an imaging system (LED box) consisting of a monochrome camera, multiple LED illumination in a diffuse reflecting chamber that produces excellent color capture in perceptual quality measured in ΔE00. We evaluate this system with respect to practical applications with emphasis on textile quality assessment. Our system of 12 LEDs produces average and maximum training ΔE00 errors around 0.7 and 2.4, respectively; and average and maximum testing ΔE00 errors around 1.5 and 5.0, respectively. This performance exceeds that of reported colorimetric camera systems, except highly specialized configurations. We find that the stability of the system to LED variability under operating conditions is good. We show that pseudoinverse estimate produces better results than the MMSE estimate under actual operating conditions.

Constrained pupil balance compensation for specific lithographic illuminator settings.

Pupil energy balances have always been considered significant elements for emersion lithography generally due to the large angle of incidence and offset imaging field. Those imbalances impact on exposure uniformity and decay pattern resolution. To overcome such shortcomings, a study on pupil compensation is discussed in this manuscript. A computational method based on a constrained optimization solution is proposed. By using a self-designed optical model of a zoomed system incorporating axicon lenses, a series of computations are developed and discussed. Also, the validity of our compensation method has been fully verified by simulations under multiple illumination settings.

Exploring the biophysicochemical alteration of green alga Asterococcus superbus interactively affected by nanoparticles, triclosan and illumination

Toxic effects on Asterococcus superbus were studied based on different combinations of P25-TiO2, nano-ZnO and triclosan under multiple illumination conditions. A full factorial design (2 × 2×2 × 3) was implemented to explore interactive effects, and to identify significant factors. The results showed illumination is the most important factor with significance and becomes one of the main reasons to affect chlorophyll pigments, photosynthesis activity, unsaturated fatty acids, mitochondria function, and cause oxidative stress. Triclosan considerably affects cell viability, photosynthesis activity, lipid peroxidation and protein structure, for which triclosan is more significant than nano-ZnO. P25 is significant for oxidative stress, antioxidant enzyme, and lipid peroxidation. P25 * nano-ZnO is the only significant interaction of pollutants, affecting macromolecules, lipid peroxidation, and photosynthesis activity. High-order interactions play significant roles in affecting multiple molecular components. Two groups of endpoints are best to reflect alga responses to interactively effects from P25, nano-ZnO, and triclosan. One is ROS, chlorophyll pigments, TBARS, area, MTT, and MMP, and the other one is chlorophyll pigments, ROS, TBARS, CAT, MTT and SOD. Our findings can be instructive for a comprehensive comparison among interactions of multiple pollutants and environmental factors in natural waters, such that more robust environmental toxicity analyses can be performed.

Illumination‐Guided Furniture Layout Optimization

AbstractLighting plays a very important role in interior design. However, in the specific problem of furniture layout recommendation, illumination has been either neglected or addressed with empirical or very simplified solutions. The effectiveness of a particular layout in its expected task performance can be greatly affected by daylighting and artificial illumination in a non‐trivial manner. In this paper, we introduce a robust method for furniture layout optimization guided by illumination constraints. The method takes into account all dominant light sources, such as sun light, skylighting and fixtures, while also being able to handle movable light emitters. For this task, the method introduces multiple generic illumination constraints and physically‐based light transport estimators, operating alongside typical geometric design guidelines, in a unified manner. We demonstrate how to produce furniture arrangements that comply with important safety, comfort and efficiency illumination criteria, such as glare suppression, under complex light‐environment interactions, which are very hard to handle using empirical or simplified models.