Array Illuminator Research Articles

Multifocal confocal microscopy using a volume holographic lenslet array illuminator.

Multifocal illumination can improve image acquisition time compared to single point scanning in confocal microscopy. However, due to an increase in the system complexity, obtaining uniform multifocal illumination throughout the field of view with conventional methods is challenging. Here, we propose a volume holographic lenslet array illuminator (VHLAI) for multifocal confocal microscopy. To obtain uniform array illumination, a super Gaussian (SG) beam has been incorporated through VHLAI with an efficiency of 43%, and implemented in a confocal microscope. The design method for a photo-polymer based volume holographic beam shaper is presented and its advantages are thoroughly addressed. The proposed system can significantly improve image acquisition time without sacrificing the quality of the image. The performance of the proposed multifocal confocal microscopy was compared with wide-field images and also evaluated by measuring optically sectioned microscopic images of fluorescence beads, florescence pollen grains, and biological samples. The proposed multifocal confocal system generates images faster without any changes in scanning devices. The present method may find important applications in high-speed multifocal microscopy platforms.

Fourier ptychography multi-parameunter neural network with composite physical priori optimization.

Fourier ptychography microscopy(FPM) is a recently developed computational imaging approach for microscopic super-resolution imaging. By turning on each light-emitting-diode (LED) located on different position on the LED array sequentially and acquiring the corresponding images that contain different spatial frequency components, high spatial resolution and quantitative phase imaging can be achieved in the case of large field-of-view. Nevertheless, FPM has high requirements for the system construction and data acquisition processes, such as precise LEDs position, accurate focusing and appropriate exposure time, which brings many limitations to its practical applications. In this paper, inspired by artificial neural network, we propose a Fourier ptychography multi-parameter neural network (FPMN) with composite physical prior optimization. A hybrid parameter determination strategy combining physical imaging model and data-driven network training is proposed to recover the multi layers of the network corresponding to different physical parameters, including sample complex function, system pupil function, defocus distance, LED array position deviation and illumination intensity fluctuation, etc. Among these parameters, LED array position deviation is recovered based on the features of brightfield to darkfield transition low-resolution images while the others are recovered in the process of training of the neural network. The feasibility and effectiveness of FPMN are verified through simulations and actual experiments. Therefore FPMN can evidently reduce the requirement for practical applications of FPM.

Self-calibrated 3D differential phase contrast microscopy with optimized illumination.

3D phase imaging recovers an object's volumetric refractive index from intensity and/or holographic measurements. Partially coherent methods, such as illumination-based differential phase contrast (DPC), are particularly simple to implement in a commercial brightfield microscope. 3D DPC acquires images at multiple focus positions and with different illumination source patterns in order to reconstruct 3D refractive index. Here, we present a practical extension of the 3D DPC method that does not require a precise motion stage for scanning the focus and uses optimized illumination patterns for improved performance. The user scans the focus by hand, using the microscope's focus knob, and the algorithm self-calibrates the axial position to solve for the 3D refractive index of the sample through a computational inverse problem. We further show that the illumination patterns can be optimized by an end-to-end learning procedure. Combining these two, we demonstrate improved 3D DPC with a commercial microscope whose only hardware modification is LED array illumination.

Depth distributions of bacteria for the Pseudomonas aeruginosa-infected burn wounds treated by methylene blue-mediated photodynamic therapy in rats: effects of additives to photosensitizer.

.SignificancePseudomonas (P.) aeruginosa, a common cause of infection in burns, acquires antibiotic resistance easily and forms biofilms efficiently. Thus, it is difficult to control P. aeruginosa infection in burn wounds, which causes lethal septicemia. Antimicrobial photodynamic therapy (aPDT) is attractive as a new strategy to treat burn wound infections with drug-resistant bacteria.AimWe examined the efficacy of methylene blue (MB)-mediated aPDT with various additives in a tissue depth-resolved manner to find conditions that minimize the bacterial invasion.ApproachWe applied MB-mediated aPDT with LED array illumination to an extensive, full-thickness burn infected with P. aeruginosa in rats for three consecutive days (days 0, 1, and 2). On day 2, the depth distributions of bacteria were assessed based on the histological analysis using Gram staining. We examined how the addition of ethylenediaminetetraacetic acid (EDTA), ethanol, and dimethyl sulfoxide (DMSO) affected the efficacy of aPDT.ResultsPure MB-mediated aPDT significantly reduced the numbers of bacteria with biofilms on the wound surface and in the epidermis compared with those for the control tissue (saline only). However, there were many bacteria in the deeper region of the tissue. In contrast, MB/EDTA/ethanol/DMSO-mediated aPDT minimized the numbers of bacteria in the broad depth region of the tissue. Still, a limited number of bacteria was observed in the subcutaneous tissue.ConclusionsThe depthwise analysis of bacteria demonstrated the efficacy of the MB-mediated aPDT with the addition of EDTA, ethanol, and DMSO in controlling burn wound infections. However, further improvement of the therapy is needed to suppress bacterial migration into the deep tissue completely.

High-resolution and sensitivity bi-directional x-ray phase contrast imaging using 2D Talbot array illuminators.

Two-dimensional (2D) Talbot array illuminators (TAIs) were designed, fabricated, and evaluated for high-resolution high-contrast x-ray phase imaging of soft tissue at 10-20 keV. The TAIs create intensity modulations with a high compression ratio on the micrometer scale at short propagation distances. Their performance was compared with various other wavefront markers in terms of period, visibility, flux efficiency, and flexibility to be adapted for limited beam coherence and detector resolution. Differential x-ray phase contrast and dark-field imaging were demonstrated with a one-dimensional, linear phase stepping approach yielding 2D phase sensitivity using unified modulated pattern analysis (UMPA) for phase retrieval. The method was employed for x-ray phase computed tomography reaching a resolution of 3 µm on an unstained murine artery. It opens new possibilities for three-dimensional, non-destructive, and quantitative imaging of soft matter such as virtual histology. The phase modulators can also be used for various other x-ray applications such as dynamic phase imaging, super-resolution structured illumination microscopy, or wavefront sensing.

Formulation of diffraction efficiencies of binary phase gratings for array illumination with ultrashort pulse beams.

We present simple formulas for the diffraction efficiencies of a binary phase grating that performs array illumination with ultrashort pulse beams. Using scalar diffraction theory, we formulated the efficiencies as a function of pulse spectral width by Fourier-transforming the complex-modulated frequency spectra of diffracted pulses in the far-field region. From the analytical simulations, we found that pulse array uniformity departs from unity as the spectral width increases, or the pulse duration decreases, thereby limiting the attainable split counts. This finding can be considered in the design of gratings for delivering controlled amounts of pulse energies to diffraction orders of interest.

Equilateral triangle hexagonal array by crossing two one‐dimensional Dammann gratings with 60°

AbstractIn this paper, we demonstrate a new two‐dimensional Dammann grating element to generate equilateral‐triangle hexagonal spot array distribution with equal intensity. This type of grating is constructed by rotating two one‐dimensional Dammann gratings through an angle of 60° to form a triangular hexagonal array illumination. In this work, a 7 × 7 spot array Dammann grating is fabricated by using electron beam lithography. We have verified the equilateral triangle hexagonal array in experiment, and measured the total diffraction efficiency of the grating up to 52%, with uniformity of 0.29. The new two‐dimensional Dammann grating with its high performance opens avenues for three‐dimensional measurement, electronic toll collection and other applications.

Control of Burn Wound Infection by Methylene Blue-Mediated Photodynamic Treatment With Light-Emitting Diode Array Illumination in Rats.

Control of burn wound infection is difficult due to the increase in drug-resistant bacteria and deteriorated immune responses. In this study, we examined the usefulness of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) with illumination by a light-emitting diode (LED) array for controlling invasive infections from the wound to inside the body for rats with an extended deep burn infected with Pseudomonas aeruginosa. An MB solution with the addition of ethanol, ethylene-diamine-tetra-acetic acid disodium salt, and dimethyl sulfoxide was used as a photosensitizer (PS). An extended deep burn was made on the dorsal skin in rats and the wounds were infected with P. aeruginosa. The rats were divided into three groups: control (no treatment; n = 14), PS mixture application alone (PS alone group; n = 10), and aPDT group (n = 14). For aPDT, after the PS mixture was applied onto the surface of infected wounds, the wounds were illuminated with a 665-nm LED array at an intensity of 45 mW/cm2 three times per treatment, with an illumination duration of 20 minutes and an interval of 10 minutes. The treatment was repeated each day for 7 consecutive days (day 0-day 6). Bacterial numbers on the wound surface and the weights and survival rates of the animals were evaluated daily. At the endpoints, bacterial numbers in the liver and blood were counted. Since the PS mixture showed high dark toxicity against P. aeruginosa in vitro, the influence of the PS mixture application onto healthy skin was also examined in vivo. Even in the aPDT group, rapid bacterial regrowth was observed on the wound surface after each day's treatment, but the geometric mean values of the bacterial numbers before and after each aPDT were considerably lower than those in the control group. Application of the PS mixture alone showed a clear bactericidal effect only at day 0, which is attributable to the formation of biofilms after day 1. Rats in the aPDT group showed a smaller weight loss, a higher ratio of no bacterial migration at the endpoints, and significantly higher survival rates than those in the other two groups. Effects of repeated application of the PS mixture onto healthy skin were not evident. Application of MB-mediated aPDT with illumination by a high-intensity LED array daily for seven consecutive days was effective for suppressing invasive infection from the wound to inside the body in rats with an extensive deep burn infected with P. aeruginosa, resulting in significant improvement of their survival. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.

Nonlinear time-lens with improved power efficiency through a discrete multilevel pump.

We report a novel, to the best of our knowledge, all-optical discrete multilevel time-lens (DM-TL) design based on cross-phase modulation (XPM). In this approach, the pump is synthesized such as the quadratic phase modulation is applied to the probe in constant-level time-bins with a maximum phase excursion of 2π. As a result, a considerable reduction in the required pump power is achieved in comparison to the conventional approach based on a parabolic pump. To illustrate the concept, the proposed DM-TL is here applied to the energy-preserving conversion of a continuous-wave (CW) signal into a train of pulses according to the theory of temporal Talbot array illuminators. We demonstrate CW-to-pulse conversion gains up to 12 at repetition rates exceeding 16 GHz, with a power saving with respect to the conventional parabolic TL that is more significant for increasing conversion gains.

Adjustable super-resolution microscopy with diffractive spot array illumination

Diffractive super-resolution spot arrays offer the possibility of adjustable super-resolution microscopic imaging. By inserting a phase-only diffractive optical element (DOE) into the illumination system of a standard microscope, super-resolution information of the sample can be obtained by spots. Here, we report an adjustable super-resolution microscopy (ASM) that the imaging resolution and the number of spot arrays can be adjusted by DOEs. The results of 3 × 3 and 5 × 5 spot arrays with 50% and 70% of the Airy spot size are, respectively, realized to support the flexibility of the ASM. The resolution test target was used as a sample to show the ASM can achieve about double-resolution experimentally, illuminated by a uniform 3 × 3 spot array with 50% of the Airy spot size under a small numerical aperture objective. Moreover, imaging of cellular mitochondria was performed, substantially realized resolution beyond the diffraction limit. The ability to adjust the super-resolution of microscopy using DOEs is of great importance for further nanoscale imaging.

Metasurface Array Illuminator Based on Fresnel Holography

A kind of array illuminators is proposed based on optical metasurface consisting of rectangular nanoholes etched in silver film. The information of the metasurface hologram comes from the binarized Fresnel hologram of the target pattern. The light spot arrays are generated through the diffraction of the metasurface hologram under the right-handed circularly polarized light illumination. The shape and layout of the light spots can be adjusted through changing the arrangement of rectangular holes. The propagation distance of our array illuminator is set at 10μm. The advantages of the metasurface array illuminator including ultrathin thickness, compact structure, higher resolution and feasible fabrication are favorable to promote the applications of the metasurface holography in optical interconnection and optical integration.

Low-cost multi-modal microscope using Raspberry Pi

This report describes a direction-dependent optical microscope operated with Raspberry Pi, with LED array illumination patterns controlled by Raspberry Pi. Images are obtained with a Raspberry Pi camera module. We demonstrate the use of Raspberry-Pi-based microscopes for multimodal imaging including bright-field microscopy, dark-field microscopy, differential phase-contrast microscopy, and polarization microscopy. We also demonstrate acquisition of direction-dependent dark-field and differential phase-contrast images. From a pair of opposite line or rectangular illumination, structures along the illumination axis were enhanced in dark-field images and differential phase-contrast images. Raspberry-Pi is open-source hardware. Raspberry-Pi-based compact, cost-effective, and multi-contrast microscopes are expected to be useful for science, technology, engineering and mathematics (STEM) education.

基于非共轴阵列照明的小型化眼底相机光学系统设计

基于非共轴阵列照明的小型化眼底相机光学系统设计

Using Lens at Aperture of Antenna for NFF and FFS

Antenna technology is developing in today’s world where data transmission is main. In such environment number of different antennas is developed for near field and far field focusing. In this paper a linear feed antenna array is presented which is a sectoral horn H-plane antenna having dielectric lens of biconvex shape are placed in the aperture. Only in h-plane our antenna focuses its beam for providing high aperture and small width of linear array illumination. For the array length illumination in the other plane the field distribution is found on the array having nice agreement of 10 GHz frequency prototype. In this paper we use CST tool for simulation.

Blue-light induced breakdown of barrier function on human retinal epithelial cells is mediated by PKC-ζ over-activation and oxidative stress

We aimed to study the time course decrease of human retinal pigment epithelium (RPE) barrier function when exposed to blue light. To this end, we cultured ARPE-19 cells on Electrical Cell-substrate Impedance Sensing (ECIS) multi-well arrays. Using an ad hoc light emitting diode (LED) array illumination system together with a set of neutral density filters and a 3-dimensional (3D) printed filter holder, cells were exposed to a gradient of irradiances of blue-light with a measured peak at 468 nm. The electrical resistance between 4 kHz and 64 kHz was recorded during the exposure. Blue light exposure induced a dose-dependent decrease in the resistances at 4 kHz, however the time course resistance at 64 kHz did not show any decrease before t = 52 h. Quantification of the barrier function using mathematical model integrated in the ECIS software showed that blue-light exposure induced a dose-dependent decrease in the barrier function associated with tight junction formation (P < 0.05). This was confirmed by the immunostaining of the tight-junction associated structural protein, Zonula occludens-1 (ZO-1). The detection of reactive oxygen species by carboxy-H2DCFDA confirmed that the blue light induced dose-dependent decrease in the barrier function is mediated by oxidative stress. On a separate experiment, blue-light exposed ARPE-19 cells were treated with 100 nM Protein Kinase C zeta (PKC-ζ) pseudo substrate inhibitor to identify underlying pathway for blue-light induced damage on the barrier function. The treatment with 100 nM PKC-ζ pseudo substrate inhibitor induced faster recovery of the barrier function compared to no treatment. Altogether our results document that blue LED light exposure decreased RPE barrier function in-vitro in a dose-dependent manner, before any cell death occurred. This damage induced by blue-light on tight junctions is mediated by oxidative stress through PKC-ζ activation. The quantification of the healing effect observed by inhibition of PKC-ζ might lead to development of high throughput wound healing assays through ECIS in the future.

Controlled Dislocations Injection in N/P Hg1−xCdxTe Photodiodes by Indentations

HgCdTe (MCT) is a widely used semiconductor material used for manufacturing high-quality infrared detectors. At Sofradir, HgCdTe is grown by liquid phase epitaxy on lattice-matched CdZnTe substrates. Low threading dislocation densities (TDD) in the low 1 × 104 dislocations/cm2 are routinely obtained. Despite these low TDD levels, these dislocations are known to affect the electrical properties of photodiodes. Dislocation electrical behavior needs a deeper understanding in order to improve the manufacturing technology and the photodiode performance. In this study, we use Vickers micro-indentations to inject extra dislocations into dedicated areas of n on p mid-wave infrared photodiodes. The photodiodes were then characterized and analyzed theoretically thanks to I(V) and I(t) measurements under F/3 flux conditions (typical focal plane array illumination) at 110 K. Microindentations were performed close to the photodiodes in order to inject controlled high to very high dislocation densities. The effect of such an injection was then studied in depth on photodiodes. The electrical results have shown that the temporal variation of the current I(t) is mostly affected by the generation of extra dislocations. The same type of degradation of I(t) was observed in focal plane arrays, which confirms that dislocations play an important role in the generation of noise defects.

Detour phase Talbot array illuminator

In this Letter, we propose a simple and effective approach for transforming a conventional Talbot array illuminator (TAI) with multilevel phase steps into a binary-phase TAI (BP-TAI) through detour phase encoding. The BP-TAI is a binary (0 π) phase-only diffractive optical element, which can be utilized to generate a large-scale focal spots array with a high compression ratio. As an example, we design a square BP-TAI with the fraction parameter β = 15 for achieving a square multifocal lattice with a high compression ratio β2. Theoretical analysis and experimental results demonstrate that the detour phase encoding is efficient for designing the BP-TAI, especially with the high compression ratio. Such results may be exploited in practical large-scale optical trapping and X-ray imaging.

New reversing freeform lens design method for LED uniform illumination with extended source and near field

In light-emitting diode (LED) array illumination (e.g. LED backlighting), obtainment of high uniformity in the harsh condition of the large distance height ratio (DHR), extended source and near field is a key as well as challenging issue. In this study, we present a new reversing freeform lens design algorithm based on the illuminance distribution function (IDF) instead of the traditional light intensity distribution, which allows uniform LED illumination in the above mentioned harsh conditions. IDF of freeform lens can be obtained by the proposed mathematical method, considering the effects of large DHR, extended source and near field target at the same time. In order to prove the claims, a slim direct-lit LED backlighting with DHR equal to 4 is designed. In comparison with the traditional lenses, illuminance uniformity of LED backlighting with the new lens increases significantly from 0.45 to 0.84, and CV(RMSE) decreases dramatically from 0.24 to 0.03 in the harsh condition. Meanwhile, luminance uniformity of LED backlighting with the new lens is obtained as high as 0.92 at the condition of extended source and near field. This new method provides a practical and effective way to solve the problem of large DHR, extended source and near field for LED array illumination.

CW-to-pulse conversion using temporal Talbot array illuminators.

We report on the linear conversion of continuous-wave (CW) laser light to optical pulses using temporal Talbot array illuminators (TAIs) with fractional orders 1/q(q≤10), implemented by use of multilevel PM and dispersive propagation in a chirped fiber Bragg grating. The generated, sub-nanosecond optical pulse trains have repetition rates in the gigahertz range and show the presence of satellite pulses originated by the finite electrical modulation bandwidth (7.5GHz). Though this fact impacts the resulting extinction ratio, an experimental comparison with time and Fresnel lenses indicates that temporal TAIs represent compact systems with high light gathering efficiency (>87%) at moderate values of compression (q≤8), which can be tailored in repetition rate, gain, or width, through the fractional Talbot order for its use in pulse compression systems fed by CW light.

Advanced active imaging system for fires based on terahertz electromagnetic waves: Experimental study of effectiveness in smoky and high-temperature environments

An active imaging system for fires is proposed, based on terahertz (THz) electromagnetic waves. The purpose of this study is to assess the effectiveness of the proposed imaging system compared with an existing system based on near-infrared (NIR) radiation. An experimental study was conducted in several fire environments using both a developed THz array illuminator and an NIR system. As a result, the target object was clearly visible with THz active imaging regardless of the presence or absence of smoke, whereas the image contrast of the target deteriorated with increasing smoke density when using NIR active imaging. There were no appreciable image changes due to temperature differences. Therefore, THz active imaging using an incoherent array illuminator seems to be an effective method to ensure visibility in a fire environment such as a room filling with smoke in the early stages of a fire.