Non-uniform Light Field Research Articles

Construction of highly active photocatalytic interfaces through light field modulation and photo-deposition of Pd sites

Anchoring noble metal sites through photo-reduction is an effective way to modulate charge distribution on photocatalytic interfaces, thereby enhancing photocatalytic performance. The irradiation field on the exposed surfaces of photocatalysts has an important influence on the morphology and distribution of noble metal sites. However, non-uniform light field derived from the scattering effects of particle-form photocatalysts hinders the well-distributed photo-deposition of noble metal sites. To address this challenge, we proposed a photo-deposition method utilizing the optical fiber coated with photocatalysts. TiO2 nanorod (NR) array was coated on the optical fiber to achieve a well-distributed irradiation filed across the NR array. This resulted in a concentration of the irradiation field primarily within the NR array, maintaining uniformly distributed light intensities throughout. Palladium (Pd) sites dominated by nanoclusters were well distributed on TiO2 NR array utilizing a photo-reduction method. These Pd sites functioned as electron acceptors, facilitating the effective separation and transfer of photo-generated carriers. Consequently, an highly active photocatalytic reaction interface was constructed, demonstrating the accumulation of a substantial concentration of holes and their efficient conversion into hydroxyl radicals (·OH). Notably, hydroxyl radicals with a concentration of 62.6 μM could be generated within 14.4 min. The construction of this efficient photocatalytic interface offers an optimal platform for accelerating photocatalytic reactions and enhancing photocatalytic efficiency.

Photodynamic therapy with light-emitting diode arrays producing different light fields induces apoptosis and necrosis in gastrointestinal cancer.

Light-emitting diodes (LEDs) have become a new light source for photodynamic therapy (PDT) because of their excellent optical properties, small size, and low cost. LED arrays have so far been designed to meet the need for accurate illumination of irregular lesions. However, LED arrays determine not only the shape of the illuminated spot but also the light field, which has a significant impact on the efficacy of PDT. We designed three types of LED arrays producing different light fields, namely an intensive LED array for a uniform light field, a sparse LED array for a non-uniform light field, and a point LED array for a Gaussian-like light field, and investigated the effect and mechanism of these light fields on PDT for gastrointestinal cancer both in vitro and in vivo. We found that intensive LED-PDT induced earlier and more serious cell death, including apoptosis and necrosis, than sparse LED-PDT and point LED-PDT. Among the three LED arrays, the intensive LED array induced cells to produce more differential proteins (DEPs), mainly related to mitochondria, ribosomes, and nucleic acids. DEPs in cells subjected to sparse LED- and point LED-PDT were mainly involved in extracellular activities. For MGC-803 tumor-bearing mice, intensive LED-PDT and point LED-PDT had better tumor ablation effect than sparse LED-PDT. Notably, recurrence was observed on day 7 after sparse LED-PDT. VCAM-1 and ICAM-1 were highly expressed in sparse LEDs-PDT treated tumor tissues and were associated tumor angiogenesis, which in turn lead to poor tumor suppression. Therefore, the type of LED array significantly affected the performance of PDT for gastrointestinal cancer. Uniform light field with low power densities work better than non-uniform and Gaussian-like light fields.

Graphitic nanosheets via two-dimensional polymerization enhancing organic all-optically controlled photorefractive performance

All-optically controlled devices are the attractive subjects due to their future applications in all-optically controlled networks and computers. In this work, two-dimensional (2D) graphite nanosheets are synthesized to improve organic photorefractive performance in the all-optical operation, i.e., the photorefractive performance under zero electric field. The synthetic process is performed by 2D-polymerizing electrophilic and nucleophilic carbon species under solvothermal effect, where [:C≡C:]2− in calcium carbide is applied as nucleophilic carbon species and [C(Cl)] in carbon tetrachloride (CCl4) as electrophilic carbon species. The polycarbonization reaction consists of 1D horizontal growth for nanoribbon and 2D vertical growth for single-layer graphene. Then, single-layer graphene nanosheets are aggregated via π–π stacking effect into 2D graphite nanosheets being composed of multilayer graphene nanosheets. Notably, the self-template characteristics induce the synchronous and alternate ongoing of three above processes. Interestingly, when these 2D graphite nanosheets are doped into organic photorefractive devices, the all-optically controlled photorefractive performance is effectively improved by enhancing the gain coefficient of two-beam coupling about 46.4% from 80.1 cm−1 of control device to 117.2 cm−1 of nanographite-doped device. This is attributed to the excellent electric conductance of 2D graphite nanosheets, which strengthens the charge separation under the nonuniform light field inside organic photorefractive devices. Then, the stronger built-in electric field will be induced so that the orientation enhancement effect is increased in organic photorefractive devices. This work provides an effective and facile approach to improve organic all-optically controlled photorefractive performance with 2D graphitic nanosheets.

Multiple aperture underwater imaging algorithm based on polarization information fusion

Underwater optical imaging is the key technology to explore the underwater mystery. However, due to the absorption and backscattering effects of the media in the underwater environment, the image acquired by the detector will be severely degraded. In order to obtain the effective underwater scene information, it is necessary to restore the acquired underwater image. The restoration technology based on differential polarization is one of the main methods of restoring the underwater images, which can suppress the background scattered light by the common-mode suppression between orthogonal polarization graphs, thus realizing the restoration of underwater image. However, the relevant research shows that the restoration effect of this method is general for the underwater non-uniform light field. The main reason is that the estimation errors of polarization degree and background scattering intensity under the condition of the non-uniform underwater light field are large. Out of the above problem, in this paper we present the multiple aperture underwater imaging technology of fused polarization information. The method uses the camera array to realize the large virtual aperture imaging system, thus obtaining the wide-angle light field information, and then to fuse the depth information of the scene to realize the accurate estimation of background scattering light intensity and polarization degree under the condition of underwater non-uniform light field. The estimated parameter value can better reflect the global characteristics of the scene. Through the imaging experiments on the targets with different polarization degrees in the turbid underwater environment, comparing with the current advanced restoration algorithm, the results show that the proposed method can effectively solve the problems of background scattering and polarization degree significant estimation error caused by non-uniform underwater light field, and obtain high-quality restoration results. Through the contrast imaging experiment of the target in the underwater environment with different turbidity concentrations, the results show that with the increase of turbidity concentration of the water, the image recovery effect of the method in this paper is gradually weakened. However, it still has a good restoration effect at a large concentration. At the same time, imaging experiments are conducted on targets in underwater environments with different sediment concentrations. The results show that the method proposed in this paper can also obtain a better restoration image in the turbid water environment containing sediment.

Large depth focus-tunable photoacoustic tomography based on clinical ultrasound array transducer

Multi-element photoacoustic tomography systems have either a non-movable focus or a non-uniform light field distribution over the region of interest, significantly limiting the depth-of-field and resolution of images. In this study, focus-tunable photoacoustic tomography (FT-PAT) based on a clinical ultrasound array transducer with uniform laser excitation was developed to achieve high-resolution imaging in deep tissue. An adjustable line-focusing structure was used to condense the laser beam, and the excited photoacoustic signal was processed via a synthetic-aperture focusing technique. Carbon rods at different depths were used to evaluate the focus-tunable ability in a tissue phantom. In vivo focus-tunable imaging performance was demonstrated by an experiment involving imaging of carbon nanoparticle-labeled living nude mouse covered by chicken breast. The signal-to-noise ratio of targets at different depths was changed by focus adjustment, which demonstrates that the FT-PAT system has potential clinical applications in deep tumor imaging and subsequent diagnoses.

Depth from a Light Field Image with Learning-Based Matching Costs

One of the core applications of light field imaging is depth estimation. To acquire a depth map, existing approaches apply a single photo-consistency measure to an entire light field. However, this is not an optimal choice because of the non-uniform light field degradations produced by limitations in the hardware design. In this paper, we introduce a pipeline that automatically determines the best configuration for photo-consistency measure, which leads to the most reliable depth label from the light field. We analyzed the practical factors affecting degradation in lenslet light field cameras, and designed a learning based framework that can retrieve the best cost measure and optimal depth label. To enhance the reliability of our method, we augmented an existing light field benchmark to simulate realistic source dependent noise, aberrations, and vignetting artifacts. The augmented dataset was used for the training and validation of the proposed approach. Our method was competitive with several state-of-the-art methods for the benchmark and real-world light field datasets.

Lightness perception for surfaces moving through different illumination levels.

Lightness perception has mainly been studied with static scenes so far. This study presents four experiments investigating lightness perception under dynamic illumination conditions. We asked participants for lightness matches of a virtual three-dimensional target moving through a light field while their eye movements were recorded. We found that the target appeared differently, depending on the direction of motion in the light field and its precise position in the light field. Lightness was also strongly affected by the choice of fixation positions with the spatiotemporal image sequence. Overall, lightness constancy was improved when observers could freely view the object, over when they were forced to fixate certain regions. Our results show that dynamic scenes and nonuniform light fields are particularly challenging for our visual system. Eye movements in such scenarios are chosen to improve lightness constancy.

Spatial and temporal aspects of chromatic adaptation and their functional significance for colour constancy.

Illumination in natural scenes changes at multiple temporal and spatial scales: slow changes in global illumination occur in the course of a day, and we encounter fast and localised illumination changes when visually exploring the non-uniform light field of three-dimensional scenes; in addition, very long-term chromatic variations may come from the environment, like for example seasonal changes. In this context, I consider the temporal and spatial properties of chromatic adaptation and discuss their functional significance for colour constancy in three-dimensional scenes. A process of fast spatial tuning in chromatic adaptation is proposed as a possible sensory mechanism for linking colour constancy to the spatial structure of a scene. The observed middlewavelength selectivity of this process is particularly suitable for adaptation to the mean chromaticity and the compensation of interreflections in natural scenes. Two types of sensory colour constancy are distinguished, based on the functional differences of their temporal and spatial scales: a slow type, operating at a global scale for the compensation of the ambient illumination; and a fast colour constancy, which is locally restricted and well suited to compensate region-specific variations in the light field of three dimensional scenes.

A Large-panel Two-CCD Camera Coordinate System with an Alternate-Eight-Matrix Look-Up-Table Method

This study proposed a novel positioning model, composing of a two-camera calibration system and an Alternate-Eight-Matrix (AEM) Look-Up-Table (LUT). Two video cameras were fixed on two sides of a large-size screen to solve the problem of field of view. The first to the fourth LUTs were used to compute the corresponding positions of specified regions on the screen captured by the camera on the right side. In these four LUTs, the coordinate mapping data of the target were stored in two matrixes, while the gray level threshold values of different positions were stored in other matrixes. Similarly, the fifth to the eighth LUTs were used to compute the corresponding positions of the specified regions on the screen captured by the camera on the left side. Experimental results showed that the proposed model can solve the problems of dead zones and non-uniform light fields, while achieving rapid and precise positioning results.

A Large Panel Two-CCD Camera Coordinate System with an Alternate-Eight-Matrix Look-Up Table Algorithm

In this study, a novel positioning model of a double-CCD cameras calibration system, with an Alternate-Eight-Matrix (AEM) Look-Up-Table (LUT), was proposed. Two CCD cameras were fixed on both sides of a large scale screen to redeem Field Of View (FOV) problems. The first to the fourth AEMLUT were used to compute the corresponding positions of intermediate blocks on the screen captured by the right side camera. In these AEMLUT for the right side camera, the coordinate mapping data of the target in a specific space were stored in two matrixes, while the gray level threshold values of different position were stored in the others. Similarly, the fifth to the eighth AEMLUT were used to compute the corresponding positions of intermediate blocks on the screen captured by the left side camera. Experimental results showed that the problems of dead angles and non-uniform light fields were solved. In addition, rapid and precision positioning results can be obtained by the proposed method.

Dynamic effect of collision phase lockout in a gas of cold “dark” atoms

In a gas of slow atoms exhibiting the effect of coherent population trapping (CPT) on the sublevels of the ground state in a spatially nonuniform light field, rare collisions destroying the CPT state initiate the irreversible exchange of momentum between radiation and atoms. This exchange is manifested as an additional force that acts on the particles and is of geometric origin; i.e., it is determined only by the structure of the field of local CPT states. When this force is not masked by the standard collision change in atomic momentum, the observation of the kinetics of the particles may provide information on the physics of the collisions.