Ring Light Research Articles

Laser filamentation in air via Mathieu modulation: ranging from trajectory-predesigned curved filament to quasi-soliton and ring light bullet.

We propose theoretically various kinds of filaments via the Mathieu modulation. Our results indicate curved filaments, in-phase and out-of-phase quasi-solitons and nonlinear light bullets can be formed successfully in air. Through calculated initial Mathieu accelerating beam (MAB), curved filament is able to propagate along a predesigned elliptical trajectory. By transforming the MAB into an axial symmetrical structure with in-phase and out-of-phase modulations, we obtain two kinds of quasi-solitons in air, respectively. The latter case can even propagate in a breathing fashion. With a ring structure of MAB, we successfully form a light bullet in air that generates a chain of intensity peaks over extended distances. These unique filaments can offer significant advantages for numerous applications, such as micro engineering of materials, THz radiation generation and attosecond physics.

Evaluation of illumination system uniformity for wide-field biomedical hyperspectral imaging

Hyperspectral imaging (HSI) systems collect both spatial (morphological) and spectral (chemical) information from a sample. HSI can provide sensitive analysis for biological and medical applications, for example, simultaneously measuring reflectance and fluorescence properties of a tissue, which together with structural information could improve early cancer detection and tumour characterisation. Illumination uniformity is a critical pre-condition for quantitative data extraction from an HSI system. Non-uniformity can cause glare, specular reflection and unwanted shading, which negatively impact statistical analysis procedures used to extract abundance of different chemical species. Here, we model and evaluate several illumination systems frequently used in wide-field biomedical imaging to test their potential for HSI. We use the software LightTools and FRED. The analysed systems include: a fibre ring light; a light emitting diode (LED) ring; and a diffuse scattering dome. Each system is characterised for spectral, spatial, and angular uniformity, as well as transfer efficiency. Furthermore, an approach to measure uniformity using the Kullback–Leibler divergence (KLD) is introduced. The KLD is generalisable to arbitrary illumination shapes, making it an attractive approach for characterising illumination distributions. Although the systems are quite comparable in their spatial and spectral uniformity, the most uniform angular distribution is achieved using a diffuse scattering dome, yielding a contrast of 0.503 and average deviation of 0.303 over a ±60° field of view with a 3.9% model error in the angular domain. Our results suggest that conventional illumination sources can be applied in HSI, but in the case of low light levels, bespoke illumination sources may offer improved performance.

Fiber-Based Optical Gun for Particle Shooting

We proposed and fabricated a fiber-based optical gun for both particle trapping and shooting. The all-fiber device is made of a coaxial core optical fiber with a center core and a coaxial circular core. The fiber has a cone-frustum-shaped tip to enable the circular core to generate a focused ring light as a trapping beam, providing a stable 3D trapping potential well. When a small particle is trapped, a Gaussian beam is launched as a shooting light at the fiber center core to push the particle away from the fiber tip along the propagation direction of the beam. Here, we find that (1) the highly focused ring field with considerably lowered focusing intensity can generate a very stable particle-trapping potential well in three dimensions and the photothermal effect is also greatly reduced due to the lower optical power requirement for trapping and (2) the shooting light with a Gaussian profile not only supplies a radiation pushing force on the small particle, but also has restrictions and guiding effects as...

Improvement of Prediction Models for Nondestructive Detection of TVB-N Using Dual-Band Vis/NIR Spectroscopic Technique

Abstract. This article discusses the influence of light source and band selection on prediction model performance. Two spectra acquisition systems for visible (Vis) and near-infrared (NIR) spectroscopy with a ring light source and a point light source were set up and compared based on the coefficient of variation (CV), signal-to-noise ratio (SNR), spectrum area change rate (ACR), and model results. Reflectance spectra of 61 pork samples were collected, and anomalous samples were eliminated by Monte Carlo method based on model cluster analysis. Partial least squares (PLS) models for total volatile basic nitrogen (TVB-N) based on a single spectral region (350-1100 nm or 1000-2500 nm) and a dual spectral region (350-2500 nm) were built to compare the influence of band choice. Based on the optimal chosen band, characteristic wavelengths were selected by competitive adaptive reweighted sampling (CARS), and a new PLS model was established. The results showed that spectra acquired with the ring light source had better stability and achieved optimal prediction models. The dual spectral region, which contained more comprehensive information on TVB-N, yielded better results than any single spectral region. Based on the dual-band spectra, a simplified PLS model using feature variables achieved a coefficient of determination in the prediction set (Rp2) of 0.8767 and standard error of prediction (SEP) of 2.8354 mg per 100 g. The results demonstrated that the choice of light source and modeling band had great influence on prediction results, and improvement of models would promote the application of Vis/NIR spectroscopy in on-line or portable detection. Keywords: Band selection, Light source, Nondestructive detection, Pork, TVB-N, Vis/NIR spectroscopy.

The application of texture features to quality control of metal surfaces

Quality assessment is an important step in production processes of metal parts. This step is required in order to check whether surface quality meets the requirements. Progress in the field of computing technologies and computer vision gives the possibility of visual surface quality control with industrial cameras and image processing methods. Authors of different papers proposed various texture feature algorithms which are suitable for different fields of images processing. In this research 27 texture features were calculated for surface images taken in different lighting conditions. Correlation coefficients between these 2D texture features and 11 roughness 3D parameters were calculated. A strong correlation between 2D features and 3D parameters occurred for images captured under ring light conditions.

A Study of Atmospheric Particles Removal in a Low Visibility Outdoor Single Image

Maximum limit of human visibility without the assistance of equipment is 1000 m based on International Commission on Illumination. The use of camera in the outdoor for the purpose of navigation, monitoring, remote sensing and robotic movement sometimes may yield images that are interrupted by haze, fog, smoke, steam and water drops. Fog is the random movement of water drops in the air that normally exists in the early morning. This disorder causes a differential image observed experiences low contrast, obscure, and difficult to identify targets. Analysis of the interference image can restore damaged image as a result of obstacles from atmospheric particles or drops of water during image observation. Generally, images with atmospheric particles contain a homogeneous texture like brightness and a heterogeneous texture which is the object that exists in the atmosphere. Pre-processing method based on the dark channel prior statistical measure of contrast vision and prior knowledge, still produces good image quality but less effective to overcome Halo problem or ring light, and strong lighting. This study aims to propel the development of machine vision industry aimed at navigation or monitoring for ground transportation, air or sea.

Research on taper zone coupling from single-core fiber to annular-core hollow beam fiber

We designed and manufactured a novel annular-core hollow beam fiber which could directly yield ring light with a central dark spot inside the beam employing MCVD technique and a custom-made fiber drawing tower. The tapered fiber zone geometric shapes at varied stretching speed between the single-core fiber and the annular-core hollow beam fiber were studied theoretically. According to the beam propagation method, the bi-tapered coupling energy transmission between these two fibers was simulated and analyzed. Moreover, by adopting a fusion splicing and stretching technique at the fiber-linked point, an effective coupling approach had been fulfilled.

Common operation metrics for storage ring light sources

Storage ring light sources aim for high operational reliability. Very often beam availability is used as an operation metric to measure the reliability. A survey of several light sources reveals that the calculation of availability varies significantly between facilities. This complicates useful comparisons of reliability. Furthermore the beam availability does not provide insight regarding reliability of beam characteristics such as orbit and beam size stability. The authors propose specific metrics to evaluate the reliability of storage ring light sources; these metrics allow a detailed and meaningful comparison across facilities. Such comparisons are useful to further optimize the reliability of storage ring light source facilities.

A Scalable and Modular Dome Illumination System for Scientific Microphotography on a Budget.

A scalable and modular LED illumination dome for microscopic scientific photography is described and illustrated, and methods for constructing such a dome are detailed. Dome illumination for insect specimens has become standard practice across the field of insect systematics, but many dome designs remain expensive and inflexible with respect to new LED technology. Further, a one-size-fits-all dome cannot accommodate the large breadth of insect size encountered in nature, forcing the photographer to adapt, in some cases, to a less than ideal dome design. The dome described here is scalable, as it is based on a isodecahedron, and the template for the dome is available as a downloaded file from the internet that can be printed on any printer, on the photographer’s choice of media. As a result, a photographer can afford, using this design, to produce a series of domes of various sizes and materials, and LED ring lights of various sizes and color temperatures, depending on the need.

An upgraded camera-based imaging system for mapping venous blood oxygenation in human skin tissue

A camera-based imaging system was previously developed for mapping venous blood oxygenation in human skin. However, several limitations were realized in later applications, which could lead to either significant bias in the estimated oxygen saturation value or poor spatial resolution in the map of the oxygen saturation. To overcome these issues, an upgraded system was developed using improved modeling and image processing algorithms. In the modeling, Monte Carlo (MC) simulation was used to verify the effectiveness of the ratio-to-ratio method for semi-infinite and two-layer skin models, and then the relationship between the venous oxygen saturation and the ratio-to-ratio was determined. The improved image processing algorithms included surface curvature correction and motion compensation. The curvature correction is necessary when the imaged skin surface is uneven. The motion compensation is critical for the imaging system because surface motion is inevitable when the venous volume alteration is induced by cuff inflation. In addition to the modeling and image processing algorithms in the upgraded system, a ring light guide was used to achieve perpendicular and uniform incidence of light. Cross-polarization detection was also adopted to suppress surface specular reflection. The upgraded system was applied to mapping of venous oxygen saturation in the palm, opisthenar and forearm of human subjects. The spatial resolution of the oxygenation map achieved is much better than that of the original system. In addition, the mean values of the venous oxygen saturation for the three locations were verified with a commercial near-infrared spectroscopy system and were consistent with previously published data.

Emittance and lifetime measurement with damping wigglers.

National Synchrotron Light Source II (NSLS-II) is a new third-generation storage ring light source at Brookhaven National Laboratory. The storage ring design calls for small horizontal emittance (<1 nm-rad) and diffraction-limited vertical emittance at 12 keV (8 pm-rad). Achieving low value of the beam size will enable novel user experiments with nm-range spatial and meV-energy resolution. The high-brightness NSLS-II lattice has been realized by implementing 30-cell double bend achromatic cells producing the horizontal emittance of 2 nm rad and then halving it further by using several Damping Wigglers (DWs). This paper is focused on characterization of the DW effects in the storage ring performance, namely, on reduction of the beam emittance, and corresponding changes in the energy spread and beam lifetime. The relevant beam parameters have been measured by the X-ray pinhole camera, beam position monitors, beam filling pattern monitor, and current transformers. In this paper, we compare the measured results of the beam performance with analytic estimates for the complement of the 3 DWs installed at the NSLS-II.

Perfect Lighting for Facial Photography in Aesthetic Surgery: Ring Light.

Photography is indispensable for plastic surgery. On-camera flashes can result in bleached out detail and colour. This is why most of the plastic surgery clinics prefer studio lighting similar to professional photographers'. In this article, we want to share a simple alternative to studio lighting that does not need extra space: Ring light. We took five different photographs of the same person with five different camera and lighting settings: Smartphone and ring light; point and shoot camera and on-camera flash; point and shoot camera and studio lighting; digital single-lens reflex (DLSR) camera and studio lighting; DSLR and ring light. Then, those photographs were assessed objectively with an online survey of five questions answered by three distinct populations: plastic surgeons (n: 28), professional portrait photographers (n: 24) and patients (n: 22) who had facial aesthetic procedures. Compared to the on-camera flash, studio lighting better showed the wrinkles of the subject. The ring light facilitated the perception of the wrinkles by providing homogenous soft light in a circular shape rather than bursting flashes. The combination of a DSLR camera and ring light gave the oldest looking subject according to 64 % of responders. The DSLR camera and the studio lighting demonstrated the youngest looking subject according to 70 % of the responders. The majority of the responders (78 %) chose the combination of DSLR camera and ring light that exhibited the wrinkles the most. We suggest using a ring light to obtain well-lit photographs without loss of detail, with any type of cameras. However, smartphones must be avoided if standard pictures are desired. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Positron annihilation Doppler broadening measurement for bulk amorphous alloy by using high energy positron generated from LCS gamma-ray at NEW SUBARU

A simple positron annihilation measurement apparatus via pair creation has been developed using high energetic gamma beam generated by laser Compton scattering (LCS) of 1 GeV electrons circulated in a storage ring and laser light with the power more than 1 W at the New SUBARU synchrotron radiation facility, University of Hyogo. This MeV ordered energy changeable positron apparatus is useful to study defects in bulk materials. In this study, the average energy of 8MeV positron was selected by the wavelength of laser light and circulated electron energy in photon factory. As a demonstrate of non-destruction positron measurement by this apparatus, positron annihilation Doppler broadening measurement has performed for bulk size of amorphous and crystal structured Zr based alloys. The larger Doppler broadening S parameter for amorphous alloy than that for crystallized one has been successfully measured.

Progress in the Design and Related Studies on the High Energy Photon Source

The High Energy Photon Source (HEPS), a kilometer-scale diffraction-limited storage ring light source, with a beam energy of 6 GeV and a natural emittance of a few tens of pm.rad, is to be built in Beijing and now is under design. In this paper we will report the progress in the design and related physical studies on the HEPS, covering issues of storage lattice design and optimization, resonance effect evaluation, booster design, injection design, collective effect study, error study, etc.

Perfect Lighting for Photography in Plastic Surgery

INTRODUCTION: Photograph is indispensable for plastic surgery. On-camera flashes can result in bleached out detail and color. This is why most of the plastic surgery clinics prefer studio lighting similar to professional photographers’.1,2 We want to share a simple alternative: Ring light (Fig. 1).Figure 1: Photograph of DIY ring light.MATERIALS AND METHODS: We took five different photographs of the same person with five different camera and lighting settings (Fig. 2): Smartphone and ring light point and shoot camera (PSC) and on- camera flash; PSC and studio lighting; digital single lens reflex (DLSR) camera and studio lighting; DSLR and ring light. Then, those photographs were assessed objectively with an online survey of five questions answered by three distinct populations: plastic surgeons (n: 28), professional portrait photographers (n: 24) and patients (n: 22) who had facial aesthetic procedure.Figure 2: Photographs of 72-year-old female subject taken with five different camera and lighting settings. Row A: Smartphone and ring light. Row B: Point and shoot camera and its on-camera flash. Row C: Point and shoot camera and ring light. Row D: Digital single lens reflex camera and studio lighting. Row E: Digital single lens reflex camera and ring light.RESULTS: Compared to the on-camera flash, studio lighting better showed the wrinkles of the subject. Ring light facilitated the perception of the wrinkles by providing homogenous soft light in circular shape rather than bursting flashes. Combination of DSLR camera and ring light gave the oldest looking subject according to 64% of responders. DSLR camera and the studio lighting demonstrated the youngest looking subject according to 70% of the responders. The majority of the responders (78%) chose the combination of DSLR camera and ring light that exhibited the wrinkles the most. CONCLUSION: We suggest using ring light to obtain well-lit photographs without loss of detail. We strongly advise not to use smartphone if you want to achieve standardized pictures.

DLSR design and plans: an international overview.

It has been known for decades that the emittance of multi-GeV storage rings can be reduced to very small values using multi-bend achromat (MBA) lattices. However, a practical design of a ring having emittance approaching the diffraction limit for multi-keV photons, i.e. a diffraction-limited storage ring (DLSR), with a circumference of order 1 km or less was not possible before the development of small-aperture vacuum systems and other accelerator technology, together with an evolution in the understanding and accurate simulation of non-linear beam dynamics, had taken place. The 3-GeV MAX IV project in Sweden has initiated a new era of MBA storage ring light source design, i.e. a fourth generation, with the Sirius project in Brazil now following suit, each having an order of magnitude smaller horizontal emittance than third-generation machines. The ESRF, APS and SPring-8 are all exploring 6-GeV MBA lattice conversions in the imminent future while China is considering a similar-energy green-field machine. Other lower-energy facilities, including the ALS, SLS, Soleil, Diamond and others, are studying the possibility of such conversions. Future larger-circumference rings, possibly housed in >2-km tunnels made available by decommissioned high-energy physics accelerators, could have sub-10-pm-rad emittances, providing very high coherence for >10-keV X-rays. A review of fourth-generation ring design concepts and plans in the world is presented.

Evaluation of the optimal exposure settings for occlusal photography with digital cameras

Background and objectiveRecently, there have been produced several kinds of camera systems, lighting devices and image processing programs. The intraoral photographs are periodically required in pediatric dentistry, since the oral environment of children changes rapidly and dramatically because of disease, growth, and tooth eruption. However, the suitable settings for intraoral digital imaging have not yet been reported. In this study, single-lens reflex and mirrorless cameras were used with a ring flash, ring light emitting diode (LED), or standard fluorescent lamp to determine the optimal exposure parameters for occlusal photography. Materials and methodsFifty-six dentists evaluated images of a discolored nonvital central incisor and first molar with recurrent caries and stained fissures clipped from a low-magnification photograph of the adult maxillary occlusal surface reflected in a mirror by using various F-numbers (representing aperture), shutter speeds, and International Organization for Standardization (ISO) numbers (representing light sensitivity). ResultsThe results showed that F-numbers between 5.6 and 10, shutter speeds faster than 1/30s, and ISO 800 produce the best occlusal images when a 60 mm f/2.8 Macro lens is used. Better images are obtained with ring LED than with ring flash. Furthermore, ISO 3200 is required for low-magnification photography in natural light. Finally, intraoral digital images should be captured under low magnification, because tilted or deflected images can be adjusted by using imaging software.

Multispectral calibration to enhance the metrology performance of C-mount camera systems

Abstract. Low cost monochrome camera systems based on CMOS sensors and C-mount lenses have been successfully applied to a wide variety of metrology tasks. For high accuracy work such cameras are typically equipped with ring lights to image retro-reflective targets as high contrast image features. Whilst algorithms for target image measurement and lens modelling are highly advanced, including separate RGB channel lens distortion correction, target image circularity compensation and a wide variety of detection and centroiding approaches, less effort has been directed towards optimising physical target image quality by considering optical performance in narrow wavelength bands. This paper describes an initial investigation to assess the effect of wavelength on camera calibration parameters for two different camera bodies and the same ‘C-mount’ wide angle lens. Results demonstrate the expected strong influence on principal distance, radial and tangential distortion, and also highlight possible trends in principal point, orthogonality and affinity parameters which are close to the parameter estimation noise level from the strong convergent self-calibrating image networks.

Rainbow Flash Camera: Depth Edge Extraction Using Complementary Colors

We present a novel color multiplexing method for extracting depth edges in a scene. It has been shown that casting shadows from different light positions provides a simple yet robust cue for extracting depth edges. Instead of flashing a single light source at a time as in conventional methods, our method flashes all light sources simultaneously to reduce the number of captured images. We use a ring light source around a camera and arrange colors on the ring such that the colors form a hue circle. Since complementary colors are arranged at any position and its antipole on the ring, shadow regions where a half of the hue circle is occluded are colorized according to the orientations of depth edges, while non-shadow regions where all the hues are mixed have a neutral color in the captured image. Thus the colored shadows in the single image directly provide depth edges and their orientations in an ideal situation. We present an algorithm that extracts depth edges from a single image by analyzing the colored shadows. We also present a more robust depth edge extraction algorithm using an additional image captured by rotating the hue circle with $$180^\circ $$ to compensate for scene textures and ambient lights. We compare our approach with conventional methods for various scenes using a camera prototype consisting of a standard camera and 8 color LEDs. We also demonstrate a bin-picking system using the camera prototype mounted on a robot arm.

Noncontact monitoring of vascular lesion phototherapy efficiency by RGB multispectral imaging

A prototype low-cost RGB imaging system consisting of a commercial RGB CMOS sensor, RGB light-emitting diode ring light illuminator, and a set of polarizers was designed and tested for mapping the skin erythema index, in order to monitor skin recovery after phototherapy of vascular lesions, such as hemangiomas and telangiectasias. The contrast of erythema index (CEI) was proposed as a parameter for quantitative characterization of vascular lesions. Skin recovery was characterized as a decrease of the CEI value relative to the value before the treatment. This approach was clinically validated by examining 31 vascular lesions before and after phototherapy.