External Illumination Research Articles

Exciton behavior under the influence of metal nanoparticle near fields: Significance of nonlocal effects

We analytically characterize the influence of a neighboring metal nanoparticle (MNP) on the behavioral trends of a quantum dot (QD) using a generalized nonlocal optical response (GNOR) method based approach, taking the MNP distance dependent modifications to the QD population relaxation and dephasing rates into account. The GNOR model is a recent generalization and an extension of the hydrodynamic Drude model (HDM), which goes beyond HDM by taking into account both the convection current and electron diffusion in the MNPs. It allows unified theoretical explanation of some experimentally observed plasmonic phenomena which otherwise would require ab initio analysis as the conventional local response approximation (LRA) fails to account for them. For example, it has been demonstrated in literature that the GNOR model captures size dependent resonance shifts of small MNPs which are unrevealed by the conventional LRA based methods, and it has proven to yield results displaying better agreement with the experimental observations for plasmonic experiments. Attempts to incorporate MNP nonlocal effects in the analytical characterization of vicinal excitons found in literature utilize the phenomenological hydrodynamic model and assume the absence of MNP interband effects. Moreover, they are only applicable to narrow parameter regions. In this paper we present a complete analytical characterization which overcomes these drawbacks and lends to the perusal of the system over wide continua of various parameters, enabling us to get an elevated view at a much lesser level of complexity compared to the conventional LRA based numerical methods or the conventional ab initio methods of accounting for the nonlocal effects. Our proposed GNOR based model predicts strong modifications to various QD properties such as population difference, absorption, MNP induced shifts to excitonic energy and F\orster enhanced broadening, coherent plasmonic field enhancement, and quantum state purity, compared to the conventional LRA based predictions. Such modifications are prominent with small MNP radii, high QD dipole moments, small detunings (of the coherent external illumination from the bare excitonic resonance), and near parameter regions exhibiting plasmonic meta resonance (PMR)-like behavior. Moreover, our complete analytical characterization enables optimization of the large system parameter space for different applications, a luxury not fully offered by the methods currently available in literature.

Melanopsin-Driven Pupil Response and Light Exposure in Non-seasonal Major Depressive Disorder.

Background: Melanopsin-expressing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) signal non-imaging forming effects of environmental light for circadian phoentrainment, the pupil light reflex, and mood regulation. In seasonal affective disorder, ipRGC dysfunction is thought to cause abberant transmission of the external illumination for photoentrainment. It is not known if patients with non-seasonal depression have abnormal melanospin mediated signaling and/or irregular environmental light exposure.Methods: Twenty-one adults who live in a sub-tropical region, including eight patients with non-seasonal depression and thirteen age-matched healthy controls were recruited. The Mini International Neuropsychiatry Interview diagnosed the presence of a major depressive disorder. Light exposure was determined using actigraphy over a 2 week period. The melanopsin mediated post-illumination pupil response (PIPR) and outer retinal inputs to ipRGCs (transient pupil response and maximum pupil constriction amplitude) were measured in response to 1 s, short and long wavelength light with high and low melanopsin excitation.Results: The mean daylight exposure as a function of clock hours and total light exposure duration (mins) to illumination levels commonly recommended for depression therapy were not significantly different between groups. Out of 84 pupil measurements (42 each in the depression and control groups), the melanopsin-mediated PIPR amplitude, transient pupil response, and pupil constriction amplitude were not significantly different between groups.Conclusions: This report provides initial evidence of normal melanopsin function and environmental light exposures in patients with pre-dominately mid and moderate non-seasonal depression in a subtropical location in the southern hemisphere.

Macroporous silicon formation by electrochemical anodization of n-type silicon without illumination

This work reports the electrochemical anodization of low-doped n-type silicon in aqueous hydrofluoride (HF) solution without the use of external illumination to generate macroporous silicon with a thin mesoporous transition layer. We have shown that pore formation during the electrochemical anodization of low-doped n-Si in the dark is due to the avalanche breakdown mechanism. Studies of dissolution valence revealed a competition between divalent direct and tetravalent indirect dissolution processes. The effect of pore morphology on anodization parameters such as applied potential, HF concentration, and anodization time was systematically investigated. The fabricated porous silicon has well-separated and straight macropores of pore diameters ranging from 89 ± 9 to 285 ± 28 nm and with limited branching or interconnectivity. Pore diameter uniformity is maintained throughout the porous layer. XRD and Raman spectroscopy have shown that the porous Si fabricated here is highly crystalline, retaining its original crystallinity. The fabricated porous Si presented in this work with tunable pore sizes, depths, and surface features can have potential applications in various fields of microelectronics, photonics, and sensors.

Device-Free Motion Detection via On-the-Air LTE Signals

Wireless signals not only carry the information of data but also encode the information of propagation environments. The motion of an object can be sensed by analyzing the variation of channel-state information. Combining the function of wireless sensing and communication will further enhance the capability of smartphones. LTE signal, which is always on the air and is seamlessly covered, is a perfect external illuminator for wireless sensing. In this letter, we study the device-free moving object detection via LTE signals. We build a prototype to receive on-the-air LTE signal and extract the real-time channel response. The existence of a moving object is recognized by the amplitude of the interfered multipath, and the moving speed is derived by the phase of the dynamic reflection. The detection probability and discovery region are investigated, and field experiments are conducted to validate the analyses.

Lighting Control Including Daylight and Energy Efficiency Improvements Analysis

Energy used for lighting is one of the major components of total energy consumption in buildings. Nowadays, buildings have a great potential to reduce their energy consumption, but to achieve this purpose additional efforts are indispensable. In this study, the need for energy savings evaluation before the implementation of lighting control algorithms for a specified building is highlighted. Therefore, experimental tests have been carried out in a university building with laboratories and other rooms, equipped with KNX building automation system. A dimmable control strategy has been investigated, dependent on daylight illuminance. Moreover, a relationship between external and internal daylight illuminance levels has been evaluated as well. Based on the experimental results, the authors proposed a method for the rough estimation of electrical energy savings. Since, according to the EN 15232 standard, Building Automation and Control Systems (BACS) play an important role in buildings’ energy efficiency improvements, the BACS efficiency factors from this standard have been used to verify the experimental results presented in the paper. The potential to reduce energy consumption from lighting in non-residential buildings by 28% for offices and 24% for educational buildings has been confirmed, but its dependence on specific building parameters has been discussed as well.

Simple Modeling of the Ratio of Fields at a Tip and a Contacting Surface with External Illumination

The analysis of the relation of fields generated at a tip and a contacting surface is performed in the Rayleigh approximation of a simple dipole model for the standard configuration of tip-enhanced Raman scattering experiments with external excitation. A comparison of the present results with the previous ones obtained for the case of tip-source reveals the role of tip-surface configuration as the amplifier of the exciting field and the stronger influence of roughness on the field distribution at external illumination, as roughness is directly excited by the external field producing second source of field in addition to the tip.

Color in television—its reproduction and perception

This paper is devoted to two features that appear when a color television image is viewed. The first feature is associated with color reproduction on the screen. The sources of color distortions in television are indicated, and it is shown that the colors of the chromaticity coordinates that lie inside the screen’s color-gamut triangle depend on the TV screen. The second feature consists of the appearance of color distortions caused by the external illumination source that is usually present when a TV receiver is being viewed. The character of these color distortions is determined.

Modification of Photoconductivity Spectra in ZnO–CdSe Quantum- Dot Composites upon Exposure to Additional Photoexcitation

The incorporation of CdS nanocrystals into a porous ZnO matrix results in sensitization of the composite in the visible spectral region. Studies of the photoconductivity spectra upon variable external illumination show that the spectra undergo reversible transformations. It is shown that the shape of the peak and the position of the local photoconductivity maximum corresponding to nanocrystals depend on the wavelength distribution of the incident radiation intensity. The mechanisms responsible for the process are discussed.

Detection of finger interruptions in silicon solar cells using photoluminescence imaging**Project supported by the National Natural Science Foundation of China (Grant Nos. 61504139 and 61275040) and the Fund from the Chinese Academy of Sciences (Grant No. Y072051002).

Finger interruptions are common problems in screen printed solar cells, resulting in poor performance in efficiency because of high effective series resistance. Electroluminescence (EL) imaging is typically used to identify interrupted fingers. In this paper, we demonstrate an alternative method based on photoluminescence (PL) imaging to identify local series resistance defects, with a particular focus on finger interruptions. Ability to detect finger interruptions by using PL imaging under current extraction is analyzed and verified. The influences of external bias control and illumination intensity on PL images are then studied in detail. Finally, in comparison with EL imaging, the using of PL imaging to identify finger interruptions possesses the prominent advantages: in PL images, regions affected by interrupted fingers show higher luminescence intensity, while regions affected by recombination defects show lower luminescence intensity. This inverse signal contrast allows PL imaging to more accurately identify the defect types.

Automated within tank fish mass estimation using infrared reflection system

Fish size and mass information during different growth stages is important for precise feeding regime management, oxygen consumption calculations, antibiotic prescription and improving fish welfare, but also to facilitate decisions on grading, harvesting and time to harvest. The main purpose of this study was to develop an automatic system to estimate fish mass using fish dorsal geometrical features and machine learning algorithms such as random forest (RF) and support vector machine (SVM). To develop the model, Kinect as a RGB-D camera was used to acquire depth map and top view images of 295 farmed seabass (Dicentrarchus labrax, L.) of different sizes. Eight dorsal geometric features were extracted and used for model development. Ten-fold cross validation was used to optimize and validate the models. Comparison of models was made in term of the coefficient of determination (Rcv2) and Root Mean Square Error of prediction (RMSEP) of cross validation. Both models exhibited significant prediction, however, SVM algorithm with Rcv2 of 0.872 (p < 0.01) and RMSE of 0.13 gave a slightly better prediction of weight compared to RF with Rcv2 of 0.868 (p < 0.01) and RMSE of 0.13 was the highest R2. Subsequently, Infrared reflection system (IREF) which is composed of a NIR range camera with an external illuminator, was also used in this study to acquire 20 fish dorsal images inside the tank. Like validation results, both algorithms had the significant prediction, however, despite the validation results, RF with R2=0.84p<0.01andRMSE= 0.12 was better in comparison to SVM with R2=0.72(p<0.01)andRMSE= 0.16. The study demonstrated that seabass geometrical dorsal features together with machine learning algorithms could be used for mass predictions. Furthermore, the IREF system can be used as a reliable, inexpensive, stress-free and accurate sensor for monitoring and estimating fish mass during cultivation within the tank.

Optical Wear Inspection of Countersink Drill Bit for Drilling Operation in Aircraft Manufacturing and Assembly Industry: A Method

Assembling aircraft skin requires thousands of rivets in order to fasten the skin together with rib. Therefore, there will be a lot of drilling operations daily. This could lead to wastage of drill bit usage if the operation is not fully utilized or reduce the hole quality if it is overused. An inspection system is developed to monitor the condition of the countersink drill bit and put these issues under control. Currently, the existing optical wear inspection system is capable to detect and measure the percentage of wear of the drill bit. The theory and application of image processing used in the detection and measurement were already discussed in previous work. In this paper, a method is proposed to inspect the wear of countersink drill bit by using the current existing system. Several key factors that may affect the accuracy of the optical inspection such as relation between illumination and image quality, and subject positioning and alignment are discussed in this paper. An external illumination system is developed to improve the quality of image captured. The drill bit positioning and alignment are corrected using image registration method in image processing. Another relevant precaution is also added into account before finally implement the complete step of performing the inspection.

Light-controlled spintronic device based on hybrid organic–inorganic perovskites

We have fabricated a spin photovoltaic device composed of a vertical spin-valve based on hybrid organic–inorganic perovskite as a spacer layer, of which resistance may be tuned by external light illumination. The magnetoconductivity of this device may be tuned from zero to reach exceptionally high values of 100 k% by controlling the illumination intensity close to the open circuit voltage. In addition, the device photocurrent can be also turned by sweeping the external magnetic field when the effects of the light intensity and applied bias voltage are judicially balanced.

Engineering Persistent Luminescence Nanoparticles for Biological Applications: From Biosensing/Bioimaging to Theranostics.

Persistent luminescence nanoparticles (PLNPs) are unique optical materials emitting long-lasting luminescence after ceasing excitation. Such a unique optical feature allows luminescence detection without constant external illumination to avoid the interferences of autofluorescence and scattering light from biological fluids and tissues. Besides, near-infrared (NIR) PLNPs have advantages of deep penetration and the reactivation of the persistent luminescence (PL) by red or NIR light. These features make the application of NIR-emitting PLNPs in long-term bioimaging no longer limited by the lifetime of PL. To take full advantage of PLNPs for biological applications, the versatile strategies for bridging PLNPs and biological system become increasingly significant for the design of PLNPs-based nanoprobes. In this Account, we summarize our systematic achievements in the biological applications of PLNPs from biosensing/bioimaging to theranostics with emphasizing the engineering strategies for fabricating specific PLNPs-based nanoprobes. We take surface engineering and manipulating energy transfer as the major principles to design various PLNPs-based nanoprobes based on the nature of interactions between nanoprobes and targets. We have developed target-induced formation or interruption of fluorescence resonance energy transfer systems for autofluorescence-free biosensing and imaging of cancer biomarkers. We have decorated single or dual targeting ligands on PLNPs for tumor-targeted imaging, and integrated other modal imaging agents into PLNPs for multimodal imaging. We have also employed specific functionalization for various biomedical applications including chemotherapy, photodynamic therapy, photothermal therapy, stem cells tracking and PL imaging-guided gene therapy. Besides, we have modified PLNPs with multiple functional units to achieve challenging metastatic tumor theranostics. The proposed design principle and comprehensive strategies show great potential in guiding the design of PLNPs nanoprobes and promoting further development of PLNPs in the fields of biological science and medicine. We conclude this Account by outlining the future directions to further promote the practical application of PLNPs. The novel protocols for the synthesis of small-size, monodisperse, and water-soluble PLNPs with high NIR PL intensity and superlong afterglow are the vibrant directions for the biomedical applications of PLNPs. In-depth theories and evidence on luminescence mechanism of PLNPs are highly desired for further improvement of their luminescence performance. Furthermore, other irradiations without tissue penetrating depth limit, such as X-ray, are encouraged for use in energy storage and re-excitation of PLNPs, enabling imaging in deep tissue in vivo and integrating other X-ray sensitized theranostic techniques such as computed tomography imaging and radiotherapy. Last but not least, PLNPs-based nanoprobes and the brand new hybrids of PLNPs with other nanomaterials show a bright prospect for accurate diagnosis and efficient treatment of diseases besides tumors.

Trapping Light in Plain Sight: Embedded Photonic Eigenstates in Zero‐Index Metamaterials

AbstractConfining electromagnetic energy is crucial to enhance light‐matter interactions, with important implications for science and technology. Here, the opportunities offered by trapping and confining light in open structures, based on the concept of embedded eigenstates within the radiation continuum enabled by zero‐index metamaterials, are discussed. Building upon the physical insights offered by the analysis, a general platform is put forward that allows the realization of extremely high field enhancements in open structures under external illumination. Structures supporting embedded eigenstates represent a rare example of physical systems in which extreme–in principle unbounded–responses can be tamed. The proposed design recipe to realize bound states in the continuum also offers a simple model that allows testing of important questions that surround the concept of embedded eigenstates, such as their effect on the local density of photonic states. The findings help clarify which nano‐optical and radio‐wave applications may benefit from this unusual and singular response.

Photodynamic therapy of balloon-injured rat carotid arteries using indocyanine green.

Photodynamic therapy (PDT) has been used to inhibit intimal hyperplasia in injured arteries. Because of the limited tissue penetration of visible light, an endovascular light source with a guided wire is often required for effective treatment. Indocyanine green (ICG), a near-infrared (NIR) photosensitizer, has been used in PDT for cancers. An extracorporeal light source may be used for shallow tissue because of the better tissue penetration of NIR light. The aim of this study was to evaluate the effect of ICG-PDT using extracorporeal NIR light on the inhibition of intimal hyperplasia in balloon-injured carotid arteries. A balloon injury (BI) model was used to induce intimal hyperplasia of carotid artery. Sprague-Dawley rats were divided into control, BI, BI + 1 × PDT, and BI + 2 × PDT groups. The control group underwent a sham procedure. PDT was performed 7days after BI. In the BI + 1 × PDT group, ICG was administered 1h before light irradiation. External illumination with 780-nm light-emitting diode light at a fluence of 4J/cm2 was applied. For the BI + 2 × PDT group, PDT was performed again at day 7, following the first PDT. Hematoxylin and eosin (H & E) staining was performed to assess vessel morphology. Arterial wall thickness was significantly larger in the BI group compared with the control group. ICG-PDT significantly reduced arterial wall thickness compared with the BI group. Repeated PDT further decreased arterial wall thickness to the level of the control group. These findings indicate a promising approach for the treatment of restenosis of carotid arteries.

Optical model of the murine lung to optimize pulmonary illumination.

We describe a Monte Carlo model of the mouse torso to optimize illumination of the mouse lung for fluorescence detection of low levels of pulmonary pathogens, specifically Mycobacterium tuberculosis. After validation of the simulation with an internally illuminated optical phantom, the entire mouse torso was simulated to compare external and internal illumination techniques. Measured optical properties of deflated mouse lungs were scaled to mimic the diffusive properties of inflated lungs in vivo. Using the full-torso model, a 2 × to 3 × improvement in average fluence rate in the lung was seen for dorsal compared with ventral positioning of the mouse with external illumination. The enhancement in average fluence rate in the lung using internal excitation was 40 × to 60 × over external illumination in the dorsal position. Parameters of the internal fiber optic source were manipulated in the model to guide optimization of the physical system and experimental protocol for internal illumination and whole-body detection of fluorescent mycobacteria in a mouse model of infection.

Internal-illumination photoacoustic computed tomography.

We report a photoacoustic computed tomography (PACT) system using a customized optical fiber with a cylindrical diffuser to internally illuminate deep targets. The traditional external light illumination in PACT usually limits the penetration depth to a few centimeters from the tissue surface, mainly due to strong optical attenuation along the light propagation path from the outside in. By contrast, internal light illumination, with external ultrasound detection, can potentially detect much deeper targets. Different from previous internal illumination PACT implementations using forward-looking optical fibers, our internal-illumination PACT system uses a customized optical fiber with a 3-cm-long conoid needle diffuser attached to the fiber tip, which can homogeneously illuminate the surrounding space and substantially enlarge the field of view. We characterized the internal illumination distribution and PACT system performance. We performed tissue phantom and in vivo animal studies to further demonstrate the superior imaging depth using internal illumination over external illumination. We imaged a 7.5-cm-deep leaf target embedded in optically scattering medium and the beating heart of a mouse overlaid with 3.7-cm-thick chicken tissue. Our results have collectively demonstrated that the internal light illumination combined with external ultrasound detection might be a useful strategy to improve the penetration depth of PACT in imaging deep organs of large animals and humans.

Identifying intestinal fibrosis and inflammation by spectroscopic photoacoustic imaging: an animal study in vivo.

Crohn's disease (CD) is a chronic autoimmune disease characterized by obstructing intestinal strictures. Conventional imaging modalities can identify the strictures but cannot characterize whether a stricture is predominantly inflammatory or fibrotic. The purpose of this study is to examine the capability of photoacoustic (PA) imaging to characterize intestinal fibrosis and inflammation in vivo. Intestinal strictures in a rat model of CD were imaged with a PA-ultrasound parallel imaging system. Internal and external illuminations were attempted, both with transcutaneous PA signal reception. The PA signal magnitudes acquired at wavelengths targeting individual molecular components and the derived functional information showed significant differences between the inflammatory and fibrotic strictures, consistent with histological inflammation and fibrosis.

Influence of CdS nanoparticles grain morphology on laser-induced absorption

Using external illumination of a 7 nanosecond (ns) doubled frequency Nd: YAG laser emitting at λ = 532 nm with frequency repetition 10 Hz it was established a possibility of significant changes of the absorption at the probing wavelength 1150 nm of continuous wave (cw) He-Ne laser for the CdS nanoparticles embedded into the PVA polymer matrix. The effect is observed only during the two beam laser coherent treatment and this effect is a consequence of interference of two coherent beams. It is shown a principal role of the grain morphology in the efficiency of the process, which is more important than the nanoparticle sizes. The photoinduced absorption is manifested in the space distribution of the probing laser beam. The principal role of the grain interfaces between the nanoparticle interfaces and the surrounding polymer matrix is shown. The effect is almost independent of the nanoparticle sizes. It may be used for laser operation by nanocomposites.

White light induced photo-thermal switching in a graphene-flake-mixed ZnO nanoparticle random laser

We experimentally demonstrate lasing mode switching within a graphene-flake-mixed ZnO nanoparticle film, in which the lasing suppression is observed when white light is illuminated on the film. The similar changes are also observed by changing the temperature of the same sample (about 30 °C increase form room temperature), while no lasing suppression is observed in a ZnO nanoparticle film without graphene flakes. In addition, we also observe that a thin glass substrate coated by a graphene-flake-mixed ZnO nanoparticle film shows a bend toward the film-coated side with increasing the white light intensity, due to the negative thermal expansion of graphene flakes. From these results, we consider that, beside the temperature dependent ZnO emission property, the photo-thermal response of graphene flakes is the dominant key for our observed lasing mode changes, in which the local structural change in a graphene-flake-mixed ZnO nanoparticle film would be induced by the white light absorption of graphene flakes. This study suggests the possibility to provide a method to remotely and non-invasively control and tune the lasing modes by external white light illumination.