Intensity Of Light Source Research Articles

The Photocatalyzed Aza-Henry Reaction of N-Aryltetrahydroisoquinolines: Comprehensive Mechanism, H•- versus H+-Abstraction, and Background Reactions

The cross-dehydrogenative coupling (CDC) reaction of N-aryltetrahydroisoquinolines (THIQ) is one of the most exploited photocatalytic transformation and a test reaction for an exceptional variety of catalysts. However, its mechanism remained unclear concerning involved intermediates, reactive pathways of the amine radical cation and the influence of oxygen and the light source. Therefore, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and synthetic methods were combined to provide a comprehensive picture of the reaction mechanism using Ru(bpy)3Cl2 as a photocatalyst under aerobic and anaerobic conditions. The reaction profiles and involved intermediates were monitored and analyzed by NMR spectroscopy. Several intermediates contributing to product formation were identified, the iminium ion, the hydroperoxide and dimer of THIQ, and a new ring opened intermediate, cleaved at the benzylic C-N bond. Mechanistic evidence is given that under anaerobic conditions preferentially the α-amino radical is formed by deprotonation, in contrast to the formation of iminium ions via H(•)-abstraction in the presence of oxygen. Further, the light-induced background reaction in the absence of the catalyst was studied in detail, revealing that the product formation rate is correlated to the intensity and wavelength of the light source and that oxygen is essential for an efficient conversion. The reaction rate and efficiency is comparable to previously reported photocatalytic systems, performed under aerobic conditions in combination with intense blue light sources. Thus, the multitude of reaction parameters investigated reveals the preference for hydrogen atom or proton abstraction in photoreactions and allows to assess the influence of experimental conditions on the mechanistic pathways.

Novel Measurement Technique for Time Dependant Intensity Variations of AC-LEDs

LEDs have surpassed incandescent and compact florescent lamps for general lighting during the last 10 years.1 Nowadays, they show very high wall plug efficiency while providing a good colour rendering index (CRI). However, flicker is still a perceivable drawback to these light sources.2 The impact and perception of flicker is increasingly investigated and its consequences for human beings range from headaches over migraines to severe neurological problems, including epileptic seizure.3 Evaluating these effects requires a number of factors to be taken into account, for instance duration of exposure, stimulated area of the retina and brightness and colour of the flickering LED source. Flicker is defined as “the rapid variation in light source intensity”.4 To describe the flicker of a light source, two metrics are currently used, flicker percentage and flicker index. Both are mathematical approaches which use the overall emission intensity and compare the minimum and the maximum intensity within a single cycle or curve integrals to gain a key figure. They do not take the wavelength, the frequency, or the duty cycle into account. The presented, novel measurement technique processes the spectrally resolved emission intensity during an adjustable amount of duty cycles, shapes and frequencies. In order to verify this measurement technique, standard phosphors such as Y3Al5O12:Ce3+ (YAG:Ce), BaMgAl10O17:Eu2+,Mn2+(BAM:Eu,Mn) have been investigated with a rectangular pulsed 50 or 100 Hz LED as excitation source. YAG:Ce showed strong flicker while BAM:Eu,Mn exhibits a flicker reducing effect. The spectrally resolved measurement technique allows us to correlate the measurement data with the eye sensitivity curve resulting in a new kind of flicker index.

English

A method for light sources estimation is proposed in this paper. The method utilizes feature points in cast shadows to estimate near light source positions from estimated source directions using specular highlights. There are several methods that can be used to estimate light sources from scene images, using either cast shadows or specular highlights. However, most of them are limited to directional light sources. The proposed method can estimate the positions and intensities of multiple near point light sources. Specular highlights on an object of known geometry are first used for light source direction estimation. Then, a discontinuity point in the object shape and the corresponding cast shadow on a ground plane are used for light source position estimation. Feature points obtained from an image of the cast shadow, however, can be inaccurate due to various factors. Information on diffused light reflected from Lambertian ground-plane surface is subsequently used to improve estimation accuracy. Experimental results were used to evaluate the performance of the proposed method.   Key words: Light source estimation, light source recovery, augmented reality.

Simple Phase Control System in Bidirectional Ring Laser

Optical sensors are commonly used and most of them detect the variation of light intensity and then if there is the uctuation of light source intensity or change in propagation loss it causes measurement errors. A ring laser sensor is one of the potential candidates which are insensitive to such uctuation, but it has mainly two problems. One is lock-in effect and the other is insensitiveness to detect the sign (polarity) of the sensing signal. To solve these problems a new phase control system has been proposed. It consists of two polarizers, two quarter-wave plates, and one Faraday rotator. Using this system the phase is controlled by the simultaneous rotation of two quarter-wave plates.

The effect of visible-light intensity on shape evolution and antibacterial properties of triangular silver nanostructures

Triangular silver nanostructures represent a novel class of nanomaterials with tunable surface plasmon resonance (SPR). By controlling the size and geometry of these structures, their SPR peaks could be tuned from the visible to the near-infrared region with numerous applications in optoelectronic, sensors, nanomedicine and specially cancer diagnosis and treatment. In this study, triangular silver nanostructures were prepared by photoinducing of spherical silver nanoparticles (NPs) with an average diameter of 10 nm. Transmission electron microscopy (TEM) and ultra violet visible (UV–Vis) spectroscopy were used to characterize silver triangles. We have found that uniform triangular silver nanostructures can be obtained using an appropriate visible-light illumination to the primary spherical silver NPs. TEM images indicated that formation of triangular structures depends on the intensity of light source. The effect of intensity of visible-light source on the geometry and size distribution of silver triangles was investigated. It was found that formation of triangular structures in addition to their size and shape evolution strongly depends on the intensity of the light illumination. Furthermore, a comparative study on the antibacterial activities of silver triangles of different sizes reveals that silver triangles experience a size-dependent interaction with the gram-negative Escherichia coli bacteria.

Enhanced terahertz wave emission from air-plasma tailored by abruptly autofocusing laser beams

Developing coherent intense broadband light sources is undoubtedly one of the key elements in pushing the frontiers of optical sciences, especially those of nonlinear terahertz (THz) optics. Plasma-based THz emitters excel in many aspects thanks to their broad radiation bandwidth, high output pulse energy and immunity to high power damage. Various excitation wavelengths and gases have been explored in the search for a stronger THz wave emission from laser-induced plasmas, whereas few attempts have been made with artificially modulated exotic wavepackets. Here we demonstrate that abruptly autofocusing-beam-induced air-plasma can give a 5.3-times enhanced THz wave pulse energy compared to normal Gaussian-beam-induced plasma under the same conditions. We believe this work will inspire a new direction for controlling THz radiation from laser-induced plasma using tools such as spatial light modulators to sculpt the excitation beams, and pave the way to THz remote spectroscopy, which is considered critical for both homeland security and environmental monitoring.

Compact extreme ultraviolet source for laboratory-based photoemission spectromicroscopy

We report on the combination of a state-of-the-art energy-filtering photoemission electron microscope with an intense yet compact laboratory-based gas discharge extreme ultraviolet (EUV) light source. Using a photon energy of 71.7 eV from oxygen plasma (O5+ spectral line), we demonstrate element-selective photoelectron imaging in real space and band structure mapping in reciprocal space. Additionally, the high surface sensitivity of the EUV light was used to study the surface oxidation on islands of the phase-change material Ge1Sb2Te4. The EUV light source allows the extension of spectromicroscopy, previously only feasible at synchrotron beamlines, to laboratory-based work.

Shock response of filled corrugated sandwich structures under extreme temperatures

Shock tube experiments were performed to investigate the blast response of corrugated steel cellular core sandwich panels filled with a silicone based syntactic foam at room and high temperatures. The syntactic foam filler was prepared by mixing a two-part silicone mixture with glass microspheres; its microstructure, and mechanical properties were also characterized. The syntactic foam-filled sandwich panels were loaded via air shock pressure by using the shock tube with a fixture capable of testing materials at temperatures up to 900℃. High-speed photo-optical methods, digital image correlation techniques, were used in tandem with optical band-pass filters and high intensity light sources for providing sufficient contrast at elevated temperatures. Back-face deformation images were captured using two synchronized high-speed cameras while a third camera captured the side view deformation images. The shock pressure profiles and digital image correlation analysis were used to obtain the impulse imparted to the specimen, transient deflection, in-plane strain and out-of-plane velocity of the back-face sheet. It was observed that using the syntactic foam as a filler material decreased the front face and back face deflections by 42% and 27%, respectively, as compared to the empty sandwich panel. At high temperatures, the silicone-based syntactic foam decomposes into silica, a stable and non-hazardous byproduct. The highest impulse was imparted to the specimen at room temperature and subsequently lower impulses with increasing temperatures were observed. Due to the increased ductility of steel at high temperatures, the specimens demonstrated an increase in back face deflection, in-plane strain and out-of-plane velocity with increased temperatures, with weld failure being the primary form of core damage.

Elimination of Light Intensity Noise Using Dual-Channel Scheme for Fiber MZI-Based FBG Sensor Interrogation

Fiber Mach–Zehnder interferometers (F-MZI) are widely used for fiber Bragg grating (FBG) sensor interrogation purpose due to their advantages in terms of wide bandwidth, high resolution, and tunable sensitivity. They are appropriate for dynamic strain measurement applications in the areas of vibration analysis, hydrophones, and acoustic emission studies. The interferometer converts the Bragg wavelength shift of an FBG sensor into a corresponding phase shift which is finally recorded as intensity variations at the output. Power fluctuations of the light source as well as disturbances in the light guiding path and/or dependence of light source intensity on wavelength introduce fictitious output intensity variations resulting into significant measurement errors. We propose and experimentally demonstrate a dual-channel F-MZI approach that eliminates the light intensity disturbance noise. Furthermore, the proposed method also improves the demodulated signal quality by a factor of $\sim 3$ dB.

Histochemical Evaluation of the Vessel Wall Destruction and Selectivity After Treatment with Intense Pulsed Light in Capillary Malformations

BackgroundAmong the different approaches for improving the effectiveness in the treatment of Capillary Malformations type Port Wine Stain (CM type PWS) are the intense pulsed light sources. There are few clinical studies prove useful in the treatment of CM. Furthermore, no studies have been published yet demonstrating the histological effects of IPL in CM. ObjectivesTo assess the histological effects of pulsed light in capillary malformations type port wine stain. We wanted to compare epidermal, dermal and vessel wall damage after treatment with different combinations of IPL parameters. Material and methodsFifty-five post-treatment biopsies were performed in 15 consenting patients with CM and stained with nitroblue-tetrazolium chloride (NBTC). Patients had not been treated previously. ResultsFifteen patients with CM, with a median age of 39 years-old were enrolled in this study. In this series, the patients with the most severe epidermal damage were those with a darker phototype. Pink CM were especially resistant to treatment, even using high fluences, short pulse durations and stacking pulses. Longer intra- and interpulse delays were effective in purple CM, achieving adequate vessel destruction. ConclusionsIPL devices provide a vast amount of treatment possibilities and further studies are necessary to optimize therapeutic approaches to CM. In this study we have observed the histological effects of different pulses on the MC type PWS.

Intense Pulsed Light Sintering of CH3NH3PbI3 Solar Cells.

Perovskite solar cells utilizing a two-step deposited CH3NH3PbI3 thin film were rapidly sintered using an intense pulsed light source. For the first time, a heat treatment has shown the capability of sintering methylammonium lead iodide perovskite and creating large crystal sizes approaching 1 μm without sacrificing surface coverage. Solar cells with an average efficiency of 11.5% and a champion device of 12.3% are reported. The methylammonium lead iodide perovskite was subjected to 2000 J of energy in a 2 ms pulse of light generated by a xenon lamp, resulting in temperatures significantly exceeding the degradation temperature of 150 °C. The process opens up new opportunities in the manufacturability of perovskite solar cells by eliminating the rate-limiting annealing step, and makes it possible to envision a continuous roll-to-roll process similar to the printing press used in the newspaper industry.

Cross Polarization for Improved Digital Image Correlation

Digital image correlation (DIC) is a surface deformation measurement technique for which accuracy and precision are sensitive to image quality. This work presents cross polarization, the use of orthogonal linear polarizers on light source(s) and camera(s), as an effective method for improving optical DIC measurements. The benefits of cross polarization are characterized through quantitative and statistical comparisons from two experiments: rigid body translation of a flat sample and uniaxial tension of a superelastic shape-memory alloy (SMA). In both experiments, cross polarization eliminated saturated pixels that degrade DIC measurements, and increased image contrast, which enabled higher spatial precision by using smaller subsets. Subset sizes are usually optimized for correlation confidence interval (typically with subsets of 21×21 px or larger), but can be decreased to achieve the highest possible spatial precision at the expense of increased correlation confidence intervals. Smaller subset sizes (such as 9×9 px) require better images to maintain correlation within error thresholds. By comparing DIC results from a uniaxial SMA tension test with unpolarized and cross-polarized images, we show that for 9×9 px subsets, the loss of valid DIC data points was reduced almost ten-fold with cross polarization. The only disadvantage we see to cross polarization is the decrease in specimen illumination due to transmission losses through the polarizers, which can easily be accommodated with sufficiently intense light sources. With the installation of relatively inexpensive linear polarizing filters, an optimum optical DIC setup can provide even better DIC measurements by delivering images without saturated pixels and with higher contrast for increased DIC spatial precision.

Near infrared spectroscopic transmittance measurements for pharmaceutical powder mixtures

This study describes the development of near infrared (NIR) calibration models using transmittance measurements in powder samples and compares the results obtained with those of tablet transmittance and diffuse reflectance of powders. Transmission near infrared spectroscopy is a method widely used for the analysis of tablets in the evaluation of drug concentration due to the larger sample volume analyzed, but not commonly used for the analysis of powder samples. Diffuse reflection near infrared spectroscopy is a method used in both powder and tablets for the evaluation of quality attributes. In this initial study NIR transmittance measurements were obtained using an off-line spectrometer equipped with a high intensity light source. Spectra were obtained with three different resolutions for the analysis of powder and tablet samples of 7.50–22.50% (w/w) acetaminophen. The Partial Least Squares (PLS) calibration models developed include pretreatments such as Standard Normal Variate (SNV) and first derivative in the region from 9500–7500cm−1. Transmittance in powder presented low Root Mean Square Error of Prediction (RMSEP) values that varied from 0.23–1.15% (w/w) APAP with resolution of 64 and 16cm−1. The lowest RMSEP values (0.23–0.39% (w/w) APAP) were obtained using a resolution of 64cm−1. The RMSEP values for powder transmittance measurements were 2.4–5.6 times lower than the diffuse reflectance measurements of the powder mixtures.

Histochemical Evaluation of the Vessel Wall Destruction and Selectivity After Treatment with Intense Pulsed Light in Capillary Malformations

BackgroundAmong the different approaches for improving the effectiveness in the treatment of Capillary Malformations type Port Wine Stain (CM type PWS) are the intense pulsed light sources. There are few clinical studies prove useful in the treatment of CM. Furthermore, no studies have been published yet demonstrating the histological effects of IPL in CM. ObjectivesTo assess the histological effects of pulsed light in capillary malformations type port wine stain. We wanted to compare epidermal, dermal and vessel wall damage after treatment with different combinations of IPL parameters. Material and methodsFifty-five post-treatment biopsies were performed in 15 consenting patients with CM and stained with nitroblue-tetrazolium chloride (NBTC). Patients had not been treated previously. ResultsFifteen patients with CM, with a median age of 39 years-old were enrolled in this study. In this series, the patients with the most severe epidermal damage were those with a darker phototype. Pink CM were especially resistant to treatment, even using high fluences, short pulse durations and stacking pulses. Longer intra- and interpulse delays were effective in purple CM, achieving adequate vessel destruction. ConclusionsIPL devices provide a vast amount of treatment possibilities and further studies are necessary to optimize therapeutic approaches to CM. In this study we have observed the histological effects of different pulses on the MC type PWS.

Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography.

Monitoring the curing kinetics of light-activated resin is a key area of research. These resins are used in restorative applications and particularly in dental applications. They can undergo volumetric shrinkage due to poor control of the depth dependent curing process, modulated by the intensity and duration of the curing light source. This often results in the formation of marginal gaps, causing pain and damage to the restoration site. In this study, we demonstrate the capabilities of a correlation method applied using a multiple references optical coherence tomography (MR-OCT) architecture to monitor the curing of the resin. A MR-OCT system is used in this study to monitor the curing of the resin. The system operates at the center wavelength of 1310 nm with an A-scan rate of 1200 A-scans per second. The axial and lateral resolution of the system is ∼13 μm and ∼27 μm. The method to determine the intensity correlation between adjacent B-frames is based on the Pearson correlation coefficient for a region of interest. Calculating the correlation coefficient for multiple B-frames related to the first B-frame at regular spaced time points, shows for a noncured resin a reduction of the correlation coefficient over time due to Brownian motion. The time constant of the reduction of the correlation value is a measure for the progress of the polymerization during LED light irradiation of the resin. The proposed approach is potentially a low-cost, powerful and unique optical imaging modality for measuring the curing behavior of dental resin and other resins, coatings, and adhesives in medical and industrial applications. To demonstrate the proposed method to monitor the curing process, a light-activated resin composite from GRADIA DIRECT ANTERIOR (GC Corporation, Japan) is studied. The curing time of resin was measured and monitored as a function of depth. The correlation coefficient method is highly sensitive to Brownian motion. The process of curing results in a change in intensity as measured by the MR-OCT signal and hence can be monitored using this method. These results show that MR-OCT has the potential to measure the curing time and monitor the curing process as a function of depth. Moreover, MR-OCT as a product has potential to be compact, low-cost and to fit into a smartphone. Using such a device for monitoring the curing of the resin will be suitable for dentists in stationary and mobile clinical settings.

Optical Characteristics of a Multichannel Hybrid Integrated Light Source for Ultra-High-Bandwidth Optical Interconnections

The optical characteristics of a multi-channel hybrid integrated light source were described for an optical interconnection with a bandwidth of over 10 Tbit/s. The power uniformity of the relative intensity of a 1000-channel light source was shown, and the minimum standard deviation s of the optical power of the 200 output ports at each 25-channel laser diode (LD) array was estimated to be 0.49 dB. This hybrid integrated light source is expected to be easily adaptable to a photonics-electronics convergence system for ultra-high-bandwidth interchip interconnections.

Simple system for measuring optical rotation of glucose solution using liquid-crystal grating

We demonstrate an optical system for measuring the concentrations of optically active media using liquid-crystal polarization gratings (LCPGs). The optical rotation angle is determined by measuring the intensities of two diffracted light beams from an LCPG combined with a quarter-wave plate (QWP). The intensity ratio is used to evaluate the optical rotation angle, minimizing the dependence on changes in light source intensity and wavelength and reducing the influence of temperature-drift-induced LC birefringence shifts. We demonstrate the system by measuring the concentration of a glucose–water solution. The measurement error caused by the slight wavelength dependence of the QWP’s retardation is assessed numerically.

Finding DNA: Using fluorescent in situ detection

It is known that DNA can be deposited onto a surface by touch yet few means have been developed for its in situ detection. Collecting touch-DNA samples can be difficult as likely locations rather than the DNA is targeted leading to many samples that are submitted to a forensic laboratory containing little or no DNA. A range of dyes are available that bind to DNA at high specificity for application within the laboratory and here we report on the use of these dyes to detect latent DNA on various substrates and within biological samples. Six common nucleic acid-binding dyes were selected due to their increase in fluorescence when in the presence of double stranded-DNA; four of the six dyes are permeable to cell membranes. The fluorescence from dye/DNA complex was detected using a high intensity light source, the Polilight® (PL500), an excitation wavelength of 490nm and emission observed/recorded through interference filters centred at 530nm or 550nm depending on the dye emission. The samples were visualised under a fluorescent microscope (Nikon Optiphot) using a B2A filter cube. The detection limit of DNA was determined for the selected dyes along with the optimal conditions, such as buffer composition and dye concentration for a range of surfaces. The ability for the dyes to detect DNA within biological samples such as saliva, hair, skin, fingermarks, and hair follicles was also determined.

Panorama of new generation of accelerator based short wavelength coherent light sources

The newly developed intense short wavelength light sources (from Extreme Ultra-Violet (EUV) to X-rays) have open the path to the exploration of matter for revealing structures and electronic processes and for following their evolution in time. After drawing the panorama of existing accelerator based short wavelength light sources, the new trends of evolution of short wavelengths FEL are described, with some illustrations with the example of the LUNEX5 (free electron Laser a New accelerator for the Exploitation of X-ray radiation of 5th generation) demonstrator project of advanced compact Free Electron Laser.

Flexible, transparent, high dielectric and photoconductive thin films using ZnO nanosheets-multi-walled carbon nanotube-polymer nanocomposites

ZnO nanosheet-Multi-Walled Carbon Nanotube (ZnO-MWCNT) nanostructures have been grown by a sol–gel chemical process. ZnO-MWCNT nanostructures were dispersed in polyvinyl alcohol (PVA) polymer solutions and spin coated on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates to fabricate a flexible, transparent, high dielectric and photoconductive thin film device. ZnO-MWCNT-PVA thin films demonstrated superior dielectric permittivity compare to ZnO-PVA and MWCNT-PVA nanocomposites. The dielectric permittivity and ac conductivity measurements of ITO/ZnO-MWCNT-PVA/Al devices have been carried out with different volume fraction of ZnO-MWCNT nanostructures. The photoconductive nature of ZnO-MWCNT-PVA composites has been investigated under illumination of broad band light source of intensity 80 mW/cm2. The flexibility study of the nanocomposite devices have been performed at different bending angles.