Showing papers on "Stray light published in 2015"

Ppb-level QEPAS NO2 sensor by use of electrical modulation cancellation method with a high power blue LED

Abstract: A novel electrical modulation cancellation method (E-MOCAM) is proposed to suppress the background noise in the case of the excitation light source with a poor beam quality. For its practical implementation, an E-MOCAM based on-beam QEPAS NO 2 sensor by use of a commercial high-power wide-stripe LED is developed. The E-MOCAM ultimately suppressed the background noise caused by the stray light by three orders of magnitude. A 1 σ detection limit of 1.3 ppb (part per billion by volume) was achieved at 1 s integration time in this experiment, which corresponds to a normalized noise equivalent absorption coefficient (NNEA) 4.2 × 10 −9 W cm −1 Hz −1/2 . A 9 h continuous on-line monitoring of ambient atmospheric NO 2 was carried out on the campus of Shanxi University.

Advancements in Rayleigh scattering thermometry by means of structured illumination

Abstract: Laser-induced Rayleigh scattering is commonly employed for two-dimensional temperature measurements and offers benefits such as high accuracy, easily interpreted data and low experimental complexity. Yet the approach suffers from an interference often referred to as stray light, an umbrella term used for all spurious light being detected. As Rayleigh scattering is an elastic scattering phenomenon, distinguishing between stray light and the signal of interest is not straightforward. In high-temperature environments, Rayleigh signals are weak due to low molecular densities, which make stray light interferences particularly cumbersome, impairing both the reliability and accuracy of Rayleigh thermometry, especially when applied in harsh combustion environments. In this paper we present an experimental solution to greatly mitigate this issue. The method, Structured Laser Illumination Planar Imaging (SLIPI), employs an intensity modulated laser light sheet to add a recognizable signature to the signal photons. This unique signature allows utilization of a post-processing algorithm that isolates and extracts the desired Rayleigh signal, thereby minimizing measurement uncertainties caused by stray light. The fidelity of the proposed method is first verified by comparing with conventional Rayleigh thermometry under ideal, i.e., stray light-free, measurement conditions. The technique is then employed under more realistic measurement conditions, where the results conclusively illustrate that the current operating range for Rayleigh thermometry can be increased significantly by means of SLIPI. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)

Toward an operational stray light correction for the Landsat 8 Thermal Infrared Sensor

Abstract: The Thermal Infrared Sensor (TIRS) onboard Landsat 8 was tasked with continuing thermal band measurements of Earth as part of the Landsat program. From first light in early 2013, there were obvious indications, such as nonuniform banding and varying absolute calibration errors, that stray light was contaminating the thermal image data collected from the instrument. Stray light in this case refers to unwanted radiance from outside the field-of-view entering the optical system and being recorded by the focal plane. Standard calibration techniques used to flat-field and radiometrically correct the data were not sufficient to adjust the image products to within the accuracy that the Landsat community has come to expect. The development of an operational technique to remove the effects of the stray light in the TIRS data has become a high priority. A methodology is presented that makes use of a stray light optical model developed for the instrument along with knowledge of the out-of-field area surrounding the TIRS earth scene. Two versions of the algorithm are proposed in which one method utilizes near-coincident image data from an external sensor while another novel method is proposed that makes use of TIRS image data itself without the need for external data. Preliminary results of the algorithm indicate that banding artifacts due to stray light are significantly reduced when the methods are applied. Additionally, initial absolute calibration error estimates of over 9K are reduced to within 2K when applying the correction methods. Although both variations of the proposed algorithm have significantly reduced the stray light effects, the fact that the latter method utilizing TIRS image data itself does not rely on any external data is a significant advantage toward the development of an operational stray light correction solution. Ongoing work is focused on operationalizing the algorithm and identifying and quantifying potential sources of error when applying the method.

Stray light and tolerance analysis of an ultrathin waveguide display.

Abstract: Waveguides are becoming increasingly popular in the field of near-eye display because of their low thickness and light weight. However, ghost stray light generated in the waveguide and the double-image problem caused by low parallelism precision seriously degrade the display quality. In this study, the causes of stray light are investigated, an effective solution is proposed, and a coupling-in structure is designed to suppress stray light. The Monte Carlo tolerances on the parallelism errors based on the visual acuity for the two substrates and the partially reflective mirror array (PRMA) of the waveguide are implemented. Results show that the fabrication accuracy of the substrates and the PRMA should be controlled within 6'' and 9'', respectively. A 2.4 mm thick waveguide with stray light of less than 1% is designed. The field of view is 36° in the pupil-expanding direction, and the diameter of the exit pupil is 11.6 mm at an eye relief of 20 mm. Finally, a proof-of-concept prototype is fabricated and demonstrated.

Compensating for the Effects of Stray Light in Single-Monochromator Brewer Spectrophotometer Ozone Retrieval

Abstract: Spectrometers are designed to isolate particular wavebands and suppress light from wavelengths outside the band of interest. However, a small amount of undesired light will always enter the detector, not through the designed optical path, but through random scattering from the instrument optical components, housing, and dust particles. Every spectrophotometer has stray light coming from outside the nominal measurement waveband. For Dobson spectrophotometers and single monochromator Brewer spectrophotometers, which are basic instruments in the World Meteorological Organization (WMO) ozone and ultraviolet (UV) monitoring network, the error introduced by stray light is substantial when the ozone slant path becomes very large because of high solar zenith angles and a thick ozone layer. These are common conditions during Arctic spring. To study the issue, a long ozone slant path Intercomparison/Calibration campaign for Nordic Brewers and Dobsons was held at Sodankyla 8–24 March 2011 and a follow-up cam...

Phase retrieval via regularization in self-diffraction-based spectral interferometry

Abstract: A novel variant of spectral phase interferometry for direct electric-field reconstruction (SPIDER) is introduced and experimentally demonstrated. Unlike most previously demonstrated variants of SPIDER, our method is based on a third-order nonlinear optical effect, namely self-diffraction (SD), rather than the second-order effect of sum-frequency generation. On the one hand, SD substantially simplifies phase-matching capabilities for multioctave spectra that cannot be hosted by second-order processes given manufacturing limitations of crystal lengths in the few-micrometer range. However, on the other hand, SD SPIDER imposes an additional constraint as it effectively measures the spectral phase of a self-convolved spectrum rather than immediately measuring the fundamental phase. Reconstruction of the latter from the measured phase and the spectral amplitude of the fundamental turns out to be an ill-posed problem, which we address by a regularization approach. We discuss the numerical implementation in detail and apply it to measured data from a Ti:sapphire amplifier system. Our experimental demonstration used 54 fs pulses and a 500 μm thick BaF2 crystal to show that the SD SPIDER signal is sufficiently strong to be separable from stray light. Extrapolating these measurements to the thinnest conceivable nonlinear media, we predict that bandwidths well above two optical octaves can be measured by a suitably adapted SD SPIDER apparatus, enabling the direct characterization of pulses down to single-femtosecond pulse durations. Such characteristics appear out of range for any currently established pulse measurement technique.

Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements

Abstract: Observations of the Sun from the Earth are always limited by the presence of the atmosphere, which strongly disturbs the images. A solution to this problem is to place the telescopes in space satellites, which produce observations without any (or limited) atmospheric aberrations. However, even though the images from space are not affected by atmospheric seeing, the optical properties of the instruments still limit the observations. In the case of diffraction limited observations, the PSF establishes the maximum allowed spatial resolution, defined as the distance between two nearby structures that can be properly distinguished. In addition, the shape of the PSF induce a dispersion of the light from different parts of the image, leading to what is commonly termed as stray light or dispersed light. This effect produces that light observed in a spatial location at the focal plane is a combination of the light emitted in the object at relatively distant spatial locations. We aim to correct the effect produced by the telescope's PSF using a deconvolution method, and we decided to apply the code on Hinode/SP quiet Sun observations. We analyze the validity of the deconvolution process with noisy data and we infer the physical properties of quiet Sun magnetic elements after the deconvolution process.

Reducing stray light transmission in near eye display using resonant grating filter

Abstract: A near eye optical display system comprising a waveguide and diffractive optical elements (DOEs) for in-coupling, exit pupil expansion, and out-coupling reduces the transmission of stray light in the system using a doubly-periodic surface relief microstructure that combines a guided-mode resonant filter with Bragg reflectance. Such resonant grating filter may be configured with grooves and/or ridges of different widths that are located on the waveguide that have respective sub-periods that match Bragg reflectance periods for particular wavelengths. The interaction of the sub-periods gives rise to a photonic band gap effect in which the resonant grating's effective refractive index is modulated to increase angular sensitivity and wavelength bandwidth of the resonant grating filter. The sub-periods define an overall period (i.e., a super period) for the resonant grating filter by which incident light is coupled into the waveguide, guided, and then coupled out of the waveguide at the side of incidence.

Design of a multiplexing grating for color holographic waveguide

Abstract: Volume holographic gratings have been used in waveguide displays to implement full-color three-dimensional imaging. Among these, multiplexing gratings are advanced in low energy losses and simple manufacture technologies when used as couplers of color hologram waveguides. A multiplexing holographic grating is designed to realize a uniform red, green, and blue diffraction efficiency and eliminate stray light to the largest extent. Results indicate that the red, green, and blue light incident normal to the grating could be successfully in-coupled into the planar waveguide for total internal reflection with high peak diffraction efficiency, similar energy output, and little stray light. We also analyze the effect of the technical tolerance, including gating thickness, index modulation, grating period, slanted angle, and incident angle. This analysis could help to minimize the optical system and improve the color image quality of waveguide displays.

Interferometric nulling of four channels with integrated optics

Abstract: Nulling interferometry has been identified as a competitive technique for the detection of extrasolar planets. In its basic form, the technique consists of combining out-of-phase a single pair of telescopes to effectively null the light of a bright star and reveal the dim glow of the companion. However, in order to mitigate the effect of the stellar leaks through the interferometer, a broad angular central null is required. The hierarchical combination of several pairs of telescopes can accomplish this task. We have manufactured and tested with monochromatic light an integrated optics component, which combines a linear array of four telescopes in the nulling mode envisaged by Angel and Woolf [Astroph. J.475, 373-379 (1997).10.1086/apj.1997.475.issue-1ASJOAB0004-637X]. By simulating in the laboratory the motion of a star in the sky, we could measure the expected angular transmission of the four-telescope nuller. Moreover, the tests have demonstrated a broad nulling scaling as the fourth power of the baseline delay.

Noise analysis for CCD-based ultraviolet and visible spectrophotometry.

Abstract: We present the results of a detailed analysis of the noise behavior of two CCD spectrometers in common use, an AvaSpec-3648 CCD UV spectrometer and an Ocean Optics S2000 Vis spectrometer. Light sources used include a deuterium UV/Vis lamp and UV and visible LEDs. Common noise phenomena include source fluctuation noise, photoresponse nonuniformity, dark current noise, fixed pattern noise, and read noise. These were identified and characterized by varying light source, spectrometer settings, or temperature. A number of noise-limiting techniques are proposed, demonstrating a best-case spectroscopic noise equivalent absorbance of 3.5×10(-4) AU for the AvaSpec-3648 and 5.6×10(-4) AU for the Ocean Optics S2000 over a 30 s integration period. These techniques can be used on other CCD spectrometers to optimize performance.

Method for in vitro assessment of straylight from intraocular lenses.

Abstract: Ocular straylight has been measured by means of psychophysical methods over the years. This approach gives a functional parameter yielding a straight comparison with optically defined light scattering, and the point-spread-function. This is of particular importance when the effect of intraocular lenses (IOLs) on postoperative straylight is sought. An optical system for straylight measurements of IOLs was adapted to a commercial device (C-Quant, Oculus), which employs such psychophysical method. The proposed modifications were validated using light-scattering filters and some sample IOLs. The measurements were performed by 3 observers to prove that results are independent from straylight of the eye. Other applications will be discussed.

Broadband spectral transmittance measurements of complex thin-film filters with optical densities of up to 12

Abstract: A new transmittance measurement setup, based on the use of a tunable laser source and a low-noise scientific-grade CCD camera operating in perfect integration mode, is proposed to achieve the spectrally resolved characterization of thin-film filters with optical densities from 0 to 12 in a wavelength range between 400 and 1000 nm. The first experimental results obtained on dedicated components demonstrate the efficiency of this new measurement scheme.

Correction of Stray-Light-Driven Interslot Radiometric Discrepancy (ISRD) Present in Radiometric Products of Geostationary Ocean Color Imager (GOCI)

Abstract: The radiometric calibration of satellite data is critical in many environmental studies and applications that are based on remote sensing data. The Geostationary Ocean Color Imager (GOCI) has suffered from what is called an interslot radiometric discrepancy (ISRD), which creates clear inconsistency between the adjacent slots in GOCI Level 1B (L1B) radiometric products, the largest source of which is currently believed to be the stray light generated in the sensor instrument. Difficulties in removing the stray-light-driven anomalies are that the intensity and the spatial extent vary with time and location, depending on the reflectance of nearby bright targets, such as cloud and land. This paper proposes an image-based correction method that removes the stray-light-driven radiometric inflation without involving an independent reference so that the method can be used for GOCI operational data processing. First, the radiometric inflation pattern is characterized by independent sources, such as Moderate Resolution Imaging Spectrometer (MODIS) data, and the inflation pattern is modeled by the minimum noise fraction transform of the input data. The modeled inflation patterns in individual slots are then adjusted across the slots in such a way that the overall ISRD in all slot boundaries is minimized. The analysis shows that the stray-light-driven radiometric anomalies can be up to 20% of the normal signals in Bands 6 (680 nm) and 8 (865 nm) of the uncorrected L1B images, and the proposed correction method reduces it to less than 2% in most of the cases, recovering the spatial continuity of natural variability across the slots.

Design and modelisation of ASPIICS optics

Abstract: In the framework of development of ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), the Centre Spatial de Liege is responsible of the optical design of the coronagraph and the optics will be manufactured by TOPTEC. The particularity of this coronagraph is to have an external occulter located 150 m ahead of the first imaging lens. This external occulter is re-imaged on an internal occulter which function is - as in a classical externally occulted Lyot coronagraph - to block the sun light diffracted by the external occulter and to reduce the straylight on the detector. The selection of this configuration is driven by the requirement to observe the corona as close as possible to the solar limb (i.e. 1 RSun) without imaging the limb itself. A requirement of 1.08 RSun is specified at optical design level to grant 1.2 Rsun at instrument level. The coronograph instrument is designed to have a field of view of 1.6° x 1.6° with a resolution of less than 6 arcsec. Its performances are limited by diffraction in a 530 – 590 nm wavelength range. This paper presents the optical design and demonstrates that by design the requirements are fulfilled within the misalignment, manufacturing and thermo-elastic error contributions.

Data processing pipeline for pointing observations of Lunar-based Ultraviolet Telescope

Abstract: We describe the data processing pipeline developed to reduce the pointing observation data of Lunar-based Ultraviolet Telescope (LUT), which belongs to the Chang’e-3 mission of the Chinese Lunar Exploration Program. The pointing observation program of LUT is dedicated to monitor variable objects in a near-ultraviolet (245–345 nm) band. LUT works in lunar daytime for sufficient power supply, so some special data processing strategies have been developed for the pipeline. The procedures of the pipeline include stray light removing, astrometry, flat fielding employing superflat technique, source extraction and cosmic rays rejection, aperture and PSF photometry, aperture correction, and catalogues archiving, etc. It has been intensively tested and works smoothly with observation data. The photometric accuracy is typically ∼0.02 mag for LUT 10 mag stars (30 s exposure), with errors come from background noises, residuals of stray light removing, and flat fielding related errors. The accuracy degrades to be ∼0.2 mag for stars of 13.5 mag which is the $5\sigma$ detection limit of LUT.

The Shadow Positioning Sensors (SPS) for formation flying metrology on-board the ESA-PROBA3 mission

Abstract: PROBA3 is an ESA technology mission devoted to in-orbit demonstration of the formation flight (FF) technique, with two satellites kept at an average inter-distance by about 144 m. The ASPIIC instrument on-board PROBA3 will be the first ever space-based coronagraph working on one satellite and having the external occulter located on the second satellite, thus allowing observations of the inner solar corona with unprecedented reduction of stray light. During the observational periods, the FF configuration will be maintained with very high precision and two different techniques will be implemented: the use of Shadow Positioning Sensors (SPS) located on the Coronagraph Spacecraft (diodes measuring the penumbral light intensity on the entrance pupil plane) and the use of Occulter Position Sensor LEDs (OPSE) located on the back side of the Occulter Spacecraft. This paper will review the main instrumental requirements on the SPS needed to determine the 3-dimensional relative positioning of the two PROBA3 satellites with high precision.

Data Processing Pipeline for Pointing Observations of Lunar-based Ultraviolet Telescope

Abstract: We describe the data processing pipeline developed to reduce the pointing observation data of Lunar-based Ultraviolet Telescope (LUT), which belongs to the Chang'e-3 mission of the Chinese Lunar Exploration Program. The pointing observation program of LUT is dedicated to monitor variable objects in a near-ultraviolet (245-345 nm) band. LUT works in lunar daytime for sufficient power supply, so some special data processing strategies have been developed for the pipeline. The procedures of the pipeline include stray light removing, astrometry, flat fielding employing superflat technique, source extraction and cosmic rays rejection, aperture and PSF photometry, aperture correction, and catalogues archiving, etc. It has been intensively tested and works smoothly with observation data. The photometric accuracy is typically ~0.02 mag for LUT 10 mag stars (30 s exposure), with errors come from background noises, residuals of stray light removing, and flat fielding related errors. The accuracy degrades to be ~0.2 mag for stars of 13.5 mag which is the 5{\sigma} detection limit of LUT.

Control of grazing angle stray light

Abstract: Compact optical assemblies for the display of an image in a head worn display with improved contrast include an image source that provides image light, a folded optic, wherein the image light passes adjacent to an optical surface of the folded optic so that stray light associated with the image light is incident onto the optical surface at a grazing angle, and a structure associated with the optical surface that prevents the stray light from reflecting off of the optical surface.

Integral imaging system optical design with aberration consideration

Abstract: Integral imaging is a technique for displaying three-dimensional images using microlens arrays. This paper discusses the optical design of an integral imaging system with aberration consideration. All previously reported systems have been analyzed and designed with only paraxial optics relations. This paper describes simulation and optimization of an integral imaging system using geometrical optics methods and OSLO optical design software. The designed system contains three arrays of microlens with spherical surfaces.

Progress on the prevention of stray light and diffraction effects on the Thai National Telescope

Abstract: The 2.4-m Thai National Telescope (TNT) is the main facility of the Thai National Observatory located on the Doi Inthanon, Thailand's highest mountain. The first astronomical images obtained at the TNT suffered from diffraction and stray light problems: bright spikes spread from bright stellar images over few arcminutes in the focal plane, and the images taken during observations in bright moon conditions were contaminated by high levels of stray light. We performed targeted investigations to identify the origin of these problems. In a first time, these investigations consisted of analyzing the irradiance distribution of defocused stellar images and of identifying the contributors. We concluded that these bright spikes around the bright stellar images were due to the chamfer and the wavefront error at the mirror edge. We thus installed an annular mask along the edge of the primary mirror that fully suppressed these spikes and we quantified the improvement by observing the double star Sirius. In a second time, we identified the contributors to the stray light by placing a pinhole camera at the TNT focal plane. Then, we designed a new baffle to improve the stray light rejection. The final design of the baffle comprises 21 diaphragms, is painted with an ordinary black paint and was designed, developed and installed on the TNT in less than 8 months. We assessed the improvement on the performance by measuring the variation of the stray light signal before and after installing the baffle in the telescope structure. These steps significantly improved the image quality and enhanced the rejection of the stray light at the focal plane level. In this paper, we present our investigations, we describe the method used to design the TNT baffle, and we present the improvement in quantitative terms.

Impact of Improved Calibration of a NEO HySpex VNIR-1600 Sensor on Remote Sensing of Water Depth

Abstract: This paper investigates at the example of bathymetry how much an application can profit from comprehensive characterizations required for an improved calibration of data from a state-of-the-art commercial hyperspectral sensor. A NEO HySpex VNIR-1600 sensor is used for this paper, and the improvements are based on measurements of sensor properties not covered by the manufacturer, in particular, detector nonlinearity and stray light. This additional knowledge about the instrument is used to implement corrections for nonlinearity, stray light, spectral smile distortion and nonuniform spectral bandwidth and to base the radiometric calibration on a SI-traceable radiance standard. Bathymetry is retrieved from a data take from the lake Starnberg using WASI-2D. The results using the original and improved calibration procedures are compared with ground reference data, with an emphasis on the effect of stray-light correction. For our instrument, stray-light biases the detector response from 416–500 nm up to 8% and from 700–760 nm up to 5%. Stray-light-induced errors affect bathymetry mainly in water deeper than Secchi depth, whereas in shallower water, the dominant error source is the calibration accuracy of the light source used for radiometric calibration. Stray-light correction reduced the systematic error of water depth by 19% from Secchi depth to three times Secchi depth, whereas the relative standard deviation remained stable at 5%.

Development of a Compact Cold Optics for Millimeter and Submillimeter Wave Observations

Abstract: We have developed an optics for 220 GHz observations, which is a compact cold re-imaging one from a telescope focal plane, with ${F}/\# = 6$ to a detector plane with ${F}/\# = 1$ at 100 mK. It employs two high refractive lenses, high purity alumina $({n}=3.1)$ and silicon $({n}=3.4)$ . To reduce the incident stray light into the detector, a cold nested baffle composed of four reflectors with the same spherical shape has been developed. The stray light power is simulated to be 0.2 $\mu$ W which corresponds a quarter of that of a without-baffles case. The total transmittance of three kinds of IR blocking filters is 0.78 at the observation frequency, and less than ${\hbox{10}}^{-10}$ above 6 THz. Thermal flow power into the detector, including the stray light power, is about 0.7 $\mu$ W. The cold optics with an 600 pixels MKID camera has been cooled down to 100 mK.

Random scattering correlated imaging system based on LED illumination, and imaging method thereof

Abstract: The invention discloses a random scattering correlated imaging system based on LED illumination, and an imaging method thereof. The random scattering correlated imaging system mainly settles the problems of high requirement for a light source, complicated imaging system and low real-time performance in imaging in prior art. The imaging system comprises the components of an LED light source (1), a collimating lens (2), a first variable diaphragm (3), an observing target (4), a random scattering medium (5), a second variable diaphragm (6), a narrowband filter plate (7) and a detector array (8). Incoherent light which is emitted from the LED light source penetrates through the collimating lens and arrives at the first variable diaphragm, and the light which penetrates through the first variable diaphragm is irradiated to the observing target. The light which carries target information enters the random scattering medium. The emergent light penetrates through the second variable diaphragm for filtering a stray light and then enters the narrowband filter plate. Finally a speckle image is formed on the detector array. The random scattering correlated imaging system and the imaging method have advantages of low imaging cost, simple imaging structure and high real-time performance in imaging. The random scattering correlated imaging system and the imaging method can be used for the fields of biomedicine, public security and anti-terrorism.

Thermal assisted magnetic recording light delivery waveguide circuit for reduced stray light induced writer protrusion

Abstract: A thermally assisted magnetic recording head is disclosed with a light delivery waveguide circuit wherein a middle section of the primary waveguide (WG) has a curved portion. In one embodiment, the curved portion connects to a front WG section at the air bearing surface (ABS) and is offset in a cross-track direction from the laser diode to prevent stray light from heating metal parts proximate to the front section and undesirable writer protrusion. Optionally, a reflective blocker is inserted between the WG spot size converter and ABS. In a second embodiment, the laser diode, spot size converter, and front WG section are all aligned along a center slider plane. The curved portion has at least one 180° bend to bend light around the blocker that is between the spot size converter and WG front section. The blocker is tilted to prevent reflected light from returning to the laser diode.

Arc flash light intensity measurement system design

Abstract: Electrical arcs emit extremely high intensity light across a wide spectrum that can damage the eye's delicate structures, such as the cornea or the retina. Developing industry safety standards to mitigate light hazards is a critical component of arc flash safety. Accurate measurement of light intensity is the first step in understanding the level of eye protection needed. Traditionally, light measurement devices are an assembly of light-detecting resistors made from cadmium sulfide (CdS) or silicon (Si) cells. However, their response times are inadequate for capturing the peak light intensity or the dynamic changes during the initial arc flash. In addition, the brightness of an arc flash is greater than the measurable light levels from traditional light measurement devices. Furthermore, the light sensitivity of traditional sensors does not match the Commission Internationale de l'Eclairage luminosity function $V(\lambda)$ curve, which defines the human eye's sensitivity to bright light as a function of wavelength under typical ambient light conditions. This paper discusses a novel light measurement technique to overcome the limitations of traditional approaches. This design is capable of measuring the light intensity of the arc flash as perceived by the human eyes. These results can be used to evaluate the potential of an arc flash to harm the eyes.

Development of junction temperature estimation system for light-emitting LED using pulsed-laser Raman scattering

Abstract: A new method by using a pulsed-laser Raman scattering technique was employed to estimate junction temperature of a fluorescence-resin-less blue-LED package. Temperature dependent Raman shift of E 2 H mode of GaN layer in the blue-LED were obtained and were in good agreement with the experimental data published by the other researchers. This technique was applied to estimation of a junction temperature of the light-emitting blue-LED. The junction temperature was successfully estimated even under the strong stray light and LED light emission. It is considered that the proposed technique would be a remote and standard system for measuring the junction temperature of light-emitting white-LEDs.