Light Emission Measurements Research Articles

Study of cosmic rays with energies above 5 EeV using radio method

At the Yakutsk array in 1986 regular measurements of radio emission produced by relativistic air shower particles were started. After monitoring of background noise in the array area frequency of 30–35 MHz was chosen, since noise level is minimal in this frequency range. During this time, air showers with highest energies of 100 EeV were registered. By using hybrid measurements of charged particles, Cherenkov light and radio emission it was shown that signal amplitude proportional to air shower energy and shape of lateral distribution at sea level correlates with the depth of maximum development. Using the obtained characteristics, atomic weight of primary particles that generated air shower was estimated within QGSjetII-04 framework simulation.

Plasmalogen oxidation induces the generation of excited molecules and electrophilic lipid species.

Plasmalogens are glycerophospholipids with a vinyl ether linkage at the sn-1 position of the glycerol backbone. Despite being suggested as antioxidants due to the high reactivity of their vinyl ether groups with reactive oxygen species, our study reveals the generation of subsequent reactive oxygen and electrophilic lipid species from oxidized plasmalogen intermediates. By conducting a comprehensive analysis of the oxidation products by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS), we demonstrate that singlet molecular oxygen [O2 (1Δg)] reacts with the vinyl ether bond, producing hydroperoxyacetal as a major primary product (97%) together with minor quantities of dioxetane (3%). Furthermore, we show that these primary oxidized intermediates are capable of further generating reactive species including excited triplet carbonyls and O2 (1Δg) as well as electrophilic phospholipid and fatty aldehyde species as secondary reaction products. The generation of excited triplet carbonyls from dioxetane thermal decomposition was confirmed by light emission measurements in the visible region using dibromoanthracene as a triplet enhancer. Moreover, O2 (1Δg) generation from dioxetane and hydroperoxyacetal was evidenced by detection of near-infrared light emission at 1,270 nm and chemical trapping experiments. Additionally, we have thoroughly characterized alpha-beta unsaturated phospholipid and fatty aldehydes by LC-HRMS analysis using two probes that specifically react with aldehydes and alpha-beta unsaturated carbonyls. Overall, our findings demonstrate the generation of excited molecules and electrophilic lipid species from oxidized plasmalogen species unveiling the potential prooxidant nature of plasmalogen-oxidized products.

New insights into the pre-ignition behavior of methane behind reflected shock waves

Pre-ignition is an undesired combustion event known to restrict kinetic modeling validation. Previous methane oxidation studies reported premature ignition as part of ignition delay time measurements in shock tubes. In this context, the effect on the pre-ignition propensity and auto-ignition behavior of stoichiometric methane mixtures at different dilution levels of hbox {N}_2, Ar, He, and hbox {CO}_2 was studied at 10 bar and 25 bar and temperatures between 1080 K and 1350 K. In addition to conventional sidewall pressure and endwall light emission measurements, a high-speed imaging setup was utilized to visualize the ignition process. Relevant physicochemical parameters to describe and predict the pre-ignition phenomenon were used. The results suggest that dilution levels up to 80% of bath gas are not successful in mitigating early ignition occurrence and its effects at moderate pressures. Replacing hbox {N}_2 by He was found to suppress early ignition at 10 bar, attributed to an enhanced dissipation of temperature inhomogeneities in the test gas section. The present findings demonstrate that hbox {CO}_2 has potential for pre-ignition heat release mitigation, while Ar was confirmed to promote premature ignition. To the best of our knowledge, we present the first detailed study on pre-ignition mitigation for methane mixtures in shock tubes, where further insights into its ignition non-idealities are given.

Multi-wavelength aperture polarimetry of debris disc host stars

ABSTRACT Debris discs around main sequence stars have been extensively characterized from infrared to millimetre wavelengths through imaging, spectroscopic, and total intensity (scattered light and/or thermal emission) measurements. Polarimetric observations have only been used sparingly to interpret the composition, structure, and size of dust grains in these discs. Here, we present new multiwavelength aperture polarization observations with parts-per-million sensitivity of a sample of twelve bright debris discs, spanning a broad range of host star spectral types, and disc properties. These measurements were mostly taken with the HIgh Precision Polarimetric Instrument on the Anglo-Australian Telescope. We combine these polarization observations with the known disc architectures and geometries of the discs to interpret the measurements. We detect significant polarization attributable to circumstellar dust from HD 377 and HD 39060, and find tentative evidence for HD 188228 and HD 202628.

Light Emission Tracking and Measurements for Analog Circuits Fault Diagnosis in Automotive Applications

Light Emission Tracking and Measurements for Analog Circuits Fault Diagnosis in Automotive Applications

Light emission processes in the context of optical beam profile monitors

Light emission from gas targets using heavy ion beam excitation is described. Typically 32S beams with ≈90 MeV (2.8 MeV/amu) particle energy were used. This study was performed in context of optical beam profile measurements. Optical transitions from neutral and singly ionized rare gases are suggested for this application. Emission spectra and their line intensities are presented for a wide range of target pressures from about 10–5 to 300 mbar. The effect of secondary electrons on the beam profiles is discussed. A comparison of ion beam and electron beam-induced spectra is shown and interpreted by a semi-quantitative model of the excitation mechanisms. Examples of beam profiles recorded with three different cameras through appropriate optical filters are presented. A comparison of projected profiles and radial profiles obtained by Abel inversion is given. Effective emission cross sections were measured for atomic and ionic lines at various target gas pressures and their pressure dependence interpreted by the excitation mechanisms. Examples of time-resolved measurements of light emission following pulsed excitation support the interpretation of the excitation mechanisms discussed in this overview of ion beam-induced light emission of gas targets.Graphical

Analyses of chemiluminescence reactions of fluorophore-linked 1,2-dioxetane isomers in crystals heating at elevated temperature including a development of a simultaneous measurement method of thermal diffusivity and light emission for a single crystal.

It has been found that a fluorophore-linked adamantylideneadamantane 1,2-dioxetane derivative showed an isomeric difference in the reactivities of crystalline-state chemiluminescence (CL) under isothermal heating conditions, while there are still unsolved problems on the conditions for intracrystalline reactions. To confirm the suitable heating conditions for initiating crystalline-state CL reactions of the isomers, the CL reactions in their crystal samples heated at elevated temperature were investigated with monitoring of CL light emission and thermogravimetry-differential thermal analysis (TG-DTA) measurements together with a simultaneous measurement method of thermal diffusivity and light emission, to provide the information on suitable temperature range for the crystalline-state CL reactions and on the reactivities depending on open and closed conditions of the crystal samples. The newly developed simultaneous measurement method provides a methodology for a single crystal to analyze the relationship between a change of the thermophysical property of inside of the crystal and the progress of a crystalline-state CL reaction.

A theoretical framework for acoustically produced luminescence: From thermometry to ultrasound pressure field mapping

Acoustically produced luminescence (APL) can be used for fast and easy mapping of ultrasound pressure fields, allowing quantitative investigation of these fields for a wide range of acoustic frequencies and pressures. APL offers a fast and inexpensive alternative for the conventional point-by-point hydrophone scanning. This can benefit industrial and medical ultrasound applications that experience stringent certification and safety requirements on pressure field characterization. APL was shown to originate from absorption-mediated heating by ultrasound irradiation of a membrane material, which consists of a polymer binder and a luminescent material (or phosphor). This heating induces local thermoluminescence emission, which is proportional to the ultrasound pressure. However, a precise framework describing the physics of the APL process, allowing the retrieval of acoustic field information from the measured light emission has been lacking. Here, we present a full theoretical model of the APL phenomenon, allowing the reconstruction of both the pressure and temperature fields from the measured luminescence. The developed theoretical model is verified using finite-element modeling and experimental validation. We then demonstrate how APL can be used to obtain a 3D reconstruction of an ultrasound pressure field, in a fast and easy way. Finally, the general model demonstrated here can also prove useful for other applications, e.g. in luminescence-based thermometry using persistent phosphors.

Investigating spray flames for nanoparticle synthesis via tomographic imaging using multi-simultaneous measurements (TIMes) of emission.

Tomographic imaging using multi-simultaneous measurements (TIMes) of spontaneous light emission was performed on various operating conditions of the SpraySyn burner to analyse the flame morphology and its potential impact on spray flame pyrolysis. Concurrent instantaneous and time-averaged three-dimensional measurements of CH* chemiluminescence (flame front indicator) and atomic Na emission from NaCl dissolved in the injected combustible liquid (related to hot burnt products of the spray flame) were reconstructed employing a 29-camera setup. Overlapping regions of CH* and Na are presented using isosurface visualisation, local correlation coefficient fields and joint probability distributions. The instantaneous results reveal the complex nature of the reacting flow and regions of interaction between the flame front with the hot gases that originate from the spray stream. The averaged reconstructions show that the spray flames tested are slightly asymmetric near the burner exit but develop into symmetric bell-shaped distributions at downstream locations. The changes in the flame structure for different operating conditions are analysed in light of previous studies, helping in the better understanding of the nanoparticle synthesis process. Furthermore, the importance of using measurements from two views for significantly improved alignment of the burner based on the originally proposed procedure are discussed in light of the reconstructions. This is an important aspect since the SpraySyn is intended for use as a well-defined standardised burner for nanoparticle synthesis, which is being investigated numerically and experimentally across different research groups.

Advancement in comprehending the evolution of nanooxides in flames using laser irradiation

Time and wavelength-resolved laser-induced incandescence (LII) study is performed in a titania nanoparticle-generating flame under different laser fluences. Measurements of the flame light emission are performed during the laser pulse and at short delay times. The results cannot be explained within the traditional description of heat exchange mechanisms between particles and the environment. The paper suggests to distinguish electron and phonon temperatures in the nanoparticles in order to reconcile observations. The fundamental phenomenon responsible for a possibility of that temperature difference and its implication to pyrometry measurements in flames is discussed and justified in the paper.

Development of real-time measurement system for emission and absorption of visible light during heavy gamma-ray irradiation

A system for the real-time measurement of the visible light emission from and absorption by a material in an intense gamma-ray field was developed. A white light-emitting diode produces a visible light beam that passes through an irradiated specimen and is measured by an ultraviolet–visible spectrophotometer through a long glass optical fiber accompanied with a Pb shielding configuration. A video camera provides real-time visual observation of the gradual change in the color state of the irradiated specimens. In order to study the formation of silver nanoparticles in detail, blue color dye was added to the radiolytic medium and its color change was examined as a function of irradiation dose to observe the interaction among radiation-introduced radicals in water, generated silver nanoparticles, and dye molecules. A mutual impact between the formation of silver nanoparticles and the deformation of the dye during gamma radiolysis are experimentally clarified. The combination of direct visual observation and optical absorption measurement is expected to provide powerful clues for elucidating various phenomena caused by irradiation effects.

Improving the External Quantum Efficiency of High-Power GaN-Based Flip-Chip LEDs by Using Sidewall Composite Reflective Micro Structure.

For high-power applications, it is important to improve the light extraction efficiency and light output of the vertical direction of LEDs. Flip-chip LEDs (FCLEDs) with an Ag/SiO2/distributed Bragg reflector/SiO2 composite reflection micro structure (CRS) were fabricated. Compared with the normal Ag-based FCLEDs, the light output power of the CRS-FCLEDs was increased by 6.3% at an operational current of 1500 mA, with the corresponding external quantum efficiency improved by 6.0%. Further investigation proved that the CRS structure exhibited higher reflectance compared with the commonly used Ag-mirror reflective structure, which originates from the increased reflective area in the sidewall and partial area of the n-GaN contact orifices. It exhibited markedly smaller optical degradation and thus higher device reliability as compared to normal Ag-based FCLED. Moreover, the light emission intensity distributions and far-field angular light emission measurements show that the CRS-FCLED has a strengthened light output in the vertical direction, which shows great potential for applications in high-power fields, such as headlamps for automobiles.

Proteins for bioinspired optical and electronic materials

Abstract

Experimental observations of exploding bridgewire detonator function

Exploding bridgewire detonators are an industry standard technology used for over 75 years and valued for their precise timing and safety characteristics. Despite widespread use, their functional mechanism remains controversial with both shock and non-shock mechanisms attributed. In this work, we reexamine the bridgewire detonator function with a suite of modern diagnostics and compare these observations with the existing literature. Traditional detonator observations consisted of voltage applied to the bridgewire and time dependent current, integral response measurements such as case motion, and more recently Schlieren imaging of the detonator surface. In this work, we add visible light emission, x-ray transmission, proton radiography, and temperature measurements during detonator function in addition to voltage, current, and function times. The addition of in situ observations of light emission, temperature, and density gives us new insight into the mechanisms of explosive bridgewire detonator function. We see a distinct separation in time, location, symmetry, and velocity of bridgewire output and detonation onset. During the time between bridgewire burst and the initiation of detonation, we observe a temperature ramp in the input pellet. In this paper, we present the suite of measurements and comparisons with the literature on integral response measurements.

A non-invasive SiC MOSFET Junction temperature estimation method based on the transient light Emission from the intrinsic body diode

A non-invasive temperature sensing method for high-voltage SiC MOSFET chips based on the measurement of light emission during reverse conduction is proposed. The method is based on a compact sensing circuit that can be easily embedded in the package, allowing online temperature estimation. The effectiveness of the circuit has been confirmed by the analysis of a commercial SiC power module. The proposed temperature sensing strategy is fast, inexpensive, accurate, and non-invasive.

On Pyrometry in Particulate-Generating Flames

ABSTRACT Pyrometry is a common tool to measure temperature and concentration of particles present in flame. It is essentially based on the measurement of light emission from flame-generated particulate assumed to be in equilibrium with the gas. In the present work the existing evidence of non-isothermality, which is the coexistence of hot and cold particles in the probe volume, is analyzed and its effect on the pyrometry measurements is considered. Light emission from titania nanoparticles produced in a flame spray is compared with that obtained irradiating the flame with a pulsed laser. The effect of the heating process on temperature and particle concentration measurements allows one to prove the coexistence of hot and cold particles in the flame before the irradiation. In order to interpret the experimental results, a thought experiment is performed to model the possible occurrence of different percentages of particles with varying temperature. The general implications to the pyrometry measurements in flames are also discussed.

Interface Formation during Collision Welding of Aluminum

Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of kinetic energy is still unclear. In this paper, the results of three series of experiments with two different setups to determine the influence of the process parameters on the fundamental phenomena and relevant mechanisms of bond formation are presented. The welding processes are monitored by different methods, like high-speed imaging, photonic Doppler velocimetry and light emission measurements. The weld interfaces are analyzed by ultrasonic investigations, metallographic analyses by optical and scanning electron microscopy, and characterized by tensile shear tests. The results provide detailed information on the influence of the different process parameters on the classical welding window and allow a prediction of the different bond mechanisms. They show that during a single magnetic pulse welding process aluminum both fusion-like and solid-state welding can occur. Furthermore, the findings allow predicting the formation of the weld interface with respect to location and shape as well as its mechanical strength.

Interface Formation during Collision Welding of Aluminum

Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of kinetic energy is still unclear. In this paper, the results of three series of experiments with two different setups to determine the influence of the process parameters on the fundamental phenomena and relevant mechanisms of bond formation are presented. The welding processes are monitored by different methods, like high-speed imaging, photonic Doppler velocimetry and light emission measurements. The weld interfaces are analyzed by ultrasonic investigations, metallographic analyses by optical and scanning electron microscopy, and characterized by tensile shear tests. The results provide detailed information on the influence of the different process parameters on the classical welding window and allow a prediction of the different bond mechanisms. They show that during a single magnetic pulse welding process aluminum both fusion-like and solid-state welding can occur. Furthermore, the findings allow predicting the formation of the weld interface with respect to location and shape as well as its mechanical strength.

Design, manufacturing and experimental validation of a bonded dual-component microstructured system for vertical light emission

This article presents a bonded dual-component microstructured planar device made of acrylic glass for vertical light emission. It features optical, cone-like undercut microstructures for efficient illumination from a light guiding plate. This microstructured light guide is designed with the help of numerical raytracing simulations for the use as an innovative luminaire for room lighting. It can also find application in display technology for efficient backlight units. To realize such undercut microstructures in acrylic glass, a variothermal injection molding process, complemented by an ultraviolet radiation assisted thermal bonding procedure is introduced. By modifying the glass transition temperature of a thin surface layer of the microstructures the undercut microstructures can be bonded thermally to a light guiding plate without any glue or solvent, while the shape of the microstructures is perfectly preserved. Measurements verify the high bonding quality and confirm the good correspondence between measured light emission and ideal optical simulations.

Measurement of Light Emission with Partial Discharge at the Stator Coil End of a Rotating Machine under Operating Temperature

Measurement of Light Emission with Partial Discharge at the Stator Coil End of a Rotating Machine under Operating Temperature