Quasi-monochromatic Light Source Research Articles

Investigation of the elimination kinetics of low and middle molecular weight uremic markers during hemodialysis treatment with the optoelectronic multispectral sensor

The elimination kinetics of conventional low-molecular weight uremic markers and advanced glycation end products (AGE products), which are considered as a possible middle molecular weight marker of uraemia in hemodialysis (HD) patients, was investigated by direct ultraviolet (UV) absorption spectroscopy of waste dialysis fluid. Light emitting diodes (LED) were exploited as quasi-monochromatic light sources in the deep UV spectral region for measuring optical transmission at the wavelengths 285 nm (the maximum of uric acid UV absorption) and 365 nm (the maximum of AGE absorption band). Optical absorption of waste dialysate was monitored during multiple HD sessions for a group of patients; the double-pool model of elimination kinetics was used for the curve fitting and approximation. It was revealed that kinetic behaviour of AGE products is almost not different comparing with uric acid and other conventional clinically proved uremic markers.

Visible-Light-Driven Methane Conversion with Oxygen Enabled by Atomically Precise Nickel Catalyst

It remains an extreme challenge to activate thermodynamically unfavorable, chemically inert methane molecules under mild conditions. Herein, we report a molecular-like nickel-thiolate hexameric clu...

Complex degree of spatial coherence over a plane irradiated by quasi-monochromatic light sources

We revisit the concept of optical spatial coherence by considering the case of the complex degree of spatial coherence induced over a plane by a quasi-monochromatic irradiating source. We apply the Van Cittert–Zernike theorem and exploit a Lloyd’s two-beam interferometer setup with its two small coherent light sources, as a way to illustrate the calculation of such complex spatial coherence, and because such setup offers a simple way to vary the separation d between its two irradiating sources, which then allows one to analytically obtain the functional dependence of the complex spatial coherence upon that separation d. We then consider the more general case in which the two small light sources of the experimental setup are spatially incoherent and again obtain the complex degree of coherence over a plane. This provides a simple, yet rigorous way, to present the subject of spatial coherences and field correlations to undergraduate physics students. An interesting link with astronomical interferometry, when images of, say, binary stellar objects are acquired, is established.

First demonstration of coherent resonant backward diffraction radiation for a quasi-monochromatic terahertz-light source

We proposed coherent resonant backward diffraction radiation (CRBDR), which generates wavelength-tunable quasi-monochromatic lights using a compact diffractor assembly in an accelerator facility of high-energy electron beams, as a unique intense terahertz (THz) light source. Superimposing the coherent backward diffracted radiation emitted by periodically arranged hollow diffractors, it is possible to amplify the frequency components satisfying a resonant condition, and make the radiation monochromatic. We demonstrated the CRBDR using the L-band linac at the Institute for Integrated Radiation and Nuclear Science at Kyoto University. It was observed that the coherent backward diffraction radiation was amplified more than three times at a frequency which was the fundamental resonant frequency in the CRBDR theory. Moreover, the number of diffractors at the saturation of the radiation power was consistent with the number estimated from the electron distribution in a bunch. The experimental results show that the CRBDR is useful as a quasi-monochromatic light source in the THz band.

Measurement setup for differential spectral responsivity of solar cells

We have developed a setup for measuring differential spectral responsivities of unifacial and bifacial solar cells under bias light conditions. The setup uses 30 high-brightness LEDs for generating a quasi-monochromatic light source covering the wavelength range 290–1300 nm. Halogen lamps are used to generate bias-lighting conditions up to the irradiance level of 1000 W/m2. The setup has been fully characterized for spectral irradiances and spatial uniformities of all light sources. Validation measurements carried out using a reference cell of 2 × 2 cm2 area from Fraunhofer ISE demonstrated an agreement better than 2% over the wavelength range of 425–940 nm, with an expanded uncertainty of 2.6%. In the UV and IR regions, the discrepancies are higher but still within estimated uncertainties. The setup is also tested in measuring spectral responsivities of large 15 × 15 cm2 bifacial solar cells. The associated problems are discussed.

Spectral characterization of solar cells and modules using LED-based solar simulators

The failure and loss analysis of solar cells relies on the precise determination of their electrical performance parameters. Light emitting diodes (LEDs) used as light sources in solar simulators provide a number of advantages compared to conventional Xenon-based solar simulators. In this work, we present an approach to rapidly measure the quantum efficiency and the reflectivity that takes the spectral broadening of the LEDs fully into account. Our approach does not rely on any specific shape of the spectral peaks and can thus be applied to any type of quasi-monochromatic light source. The two proposed methods yield valuable additional information on the solar cell performance and material properties that cannot be obtained by conventional solar simulators. Using LED solar simulators, they are completely in-line capable as they can be performed in less than one second.

The nonlinearity measurement of charge-coupled device array spectrometer using colorful LED

A nonlinearity measurement of the charge-coupled device (CCD) array spectrometer using flux addition and comparison method is described. The light with various colors from the colorful light emitting diode (LED) light source is applied to measure the nonlinearity of the spectrometer at different wavelengths, respectively. An high-end CCD array spectrometer is tested. For colorful LED light sources, the nonlinearity factors of the CCD array spectrometer (absolute value) are as follows: k<0.8% for white light, k <1.1% for red light, k <2.2% for green light and k<4.7% for blue light. By using those quasi-monochromatic light sources, it is shown that the nonlinearity depends on the wavelength. It is important to be wariness about the spectral nonlinearity and related uncertainty evaluation when the narrow-band light source is tested.

Color Conversion of GaN-Based Micro Light-Emitting Diodes Using Quantum Dots

Using CdSe/ZnS quantum dots (QDs) excited by the blue light emission of GaN-based micro light-emitting diodes (LEDs), quasi-monochromatic red light sources with emission wavelength of 625 nm were obtained. In order to enhance the blue light emission of GaN-based LEDs for further excitation of QDs, distributed/hybrid Bragg reflectors and zinc oxide (ZnO) nanorod array were, respectively, introduced to the top/bottom and top sides of GaN-based micro LEDs. The presence of ZnO nanorod array helps to channel the blue light to pump the CdSe/ZnS QDs for enhancing the red light emission. The electroluminescence of micro QDs-LEDs with reflectors and ZnO nanorod array was increased by 57.4% compared with the micro QDs-LEDs alone. The international commission on illumination chromaticity coordinate of the micro QDs-LEDs with reflectors and ZnO nanorod array was very close to the red light emission at (0.59, 0.26).

High-speed 3D imaging using two-wavelength parallel-phase-shift interferometry.

High-speed three dimensional imaging based on two-wavelength parallel-phase-shift interferometry is presented. The technique is demonstrated using a high-resolution polarization-based Linnik interferometer operating with three high-speed phase-masked CCD cameras and two quasi-monochromatic modulated light sources. The two light sources allow for phase unwrapping the single source wrapped phase so that relatively high step profiles having heights as large as 3.7 μm can be imaged in video rate with ±2 nm accuracy and repeatability. The technique is validated using a certified very large scale integration (VLSI) step standard followed by a demonstration from the semiconductor industry showing an integrated chip with 2.75 μm height copper micro pillars at different packing densities.

Determination of surface roughness of plane optical components using quasimonochromatic light source and phase shifting interferometry

A differential interferometric technique for the measurement of surface roughness of plane optical surfaces is proposed. A polarization Sagnac interferometer, placed in the image space of a reflection microscope system with linearly polarized, spatially coherent, quasimonochromatic incident beam illumination, splits the image-forming beam from a plane test surface (TS) into laterally sheared (LS) linear orthogonal components. The LS components interfere when brought to the same state of polarization. The optical path difference (OPD) variation along the direction of lateral shear is a measure of the slope variation on the TS. Polarization phase shifting interferometry has been applied to extract the OPD variation and thus the slope distribution, slope errors, and, subsequently, height errors. System error contribution is eliminated by combining height error data obtained for parallel sections of the TS that lie along a section of the image field parallel to the direction of lateral shear, as the TS is shifted in a direction normal to the lateral shear direction between the data capture. Results obtained for an aluminized plane polished TS are presented.

Effective Color Conversion of GaN-Based LEDs via Coated Phosphor Layers

Gallium nitride (GaN)-based light-emitting diodes (LEDs) equipped with distributed Bragg reflectors (DBR) and covered with either red or green phosphor layers are fabricated to form quasi-monochromatic red or green light sources. Titanium oxide and silicon oxide layers are alternately deposited to form the DBR with high reflectivity of 94.6% at 450 nm on the top of the GaN LEDs. The upward propagating blue light is reflected back by the DBR to excite the red or green phosphor layer at the bottom of GaN LEDs, producing additional fluorescence. However, there is still some blue light emitted out from the DBR and the side wall of the LEDs. Therefore, to obtain more intensive and pure monochromatic red or green light, another red (or green) phosphor thin layer is coated on the DBR. Thus, fabricated LEDs with phosphor layers on both the top and bottom surface show satisfactory monochromaticity and conversion efficiency.

Color sensitivity of the multi-exposure HDR imaging process

Abstract Multi-exposure high dynamic range(HDR) imaging builds HDR radiance maps by stitching together different views of a same scene with varying exposures. Practically, this process involves converting raw sensor data into low dynamic range (LDR) images, estimate the camera response curves, and use them in order to recover the irradiance for every pixel. During the export, applying white balance settings and image stitching, which both have an influence on the color balance in the final image. In this paper, we use a calibrated quasi-monochromatic light source, an integrating sphere, and a spectrograph in order to evaluate and compare the average spectral response of the image sensor. We finally draw some conclusion about the color consistency of HDR imaging and the additional steps necessary to use multi-exposure HDR imaging as a tool to measure the physical quantities such as radiance and luminance.

Wiener–Khintchin theorem for spatial coherence of optical wave field

The application of the Wiener–Khintchin theorem for determining the functions of the transversal and longitudinal spatial coherence of the optical field, depending on the parameters of the angular and temporal frequency spectra of the field, is considered. Based on the Wiener–Khintchin theorem, the possibility to derive the van Cittert–Zernike theorem for transversal and longitudinal spatial coherence of the optical field of a spatially incoherent quasi-monochromatic light source is shown. An expression for the dependence of the longitudinal coherence length of the optical field on the width of the frequency and width of the angular spectra of the field is obtained. The results of the interference experiment confirming the dependence of the longitudinal coherence length on the parameters of angular and frequency spectra of the field are presented.

Measurement of wedge angle of a transparent parallel plate using quasi-monochromatic light source and phase shifting interferometry

A new technique (to our knowledge), for the measurement of residual wedge angle (RWA) of high optical quality transparent nearly parallel plate (PP), using a quasi-monochromatic light source, is presented. Advantages and drawbacks of the technique and the results obtained for a PP, using a filtered white light source, is discussed. A slightly modified optical setup for accurate determination of RWA, using phase shifting interferometry (PSI), has been described. Results obtained, applying PSI, for a validation experiment and for the determination of RWA of a quasi-PP is presented. The PSI based technique does not suffer from any measurement ambiguities due to limitation in effective beam aperture. Hence the technique is suitable for high accuracy measurement of RWA of PP. In both the optical setups, presented in this paper, the respective interfering beams travel the same optical circuit and are thus subject to same perturbation in optical path, due to external mechanical vibration, which finally cancels out. Thus the measurements are much less affected by external vibrations. Since the respective interfering beams undergo identical reflections and transmissions, the visibility or contrast of the interference fringes is very good.

Bandwidth Measurement Method for Quasi-Monochromatic Light Sources

In this paper, a new method of quasi-monochromatic light source bandwidth measurement is presented. It is based on the depolarization of partially coherent light in birefringent crystals. The described method has been applied for various types of light sources to illustrate its strengths and limitations. The results of bandwidth measurements for a quasi-monochromatic laser diode at different diode currents are also presented.

A 5-Year Study of a New Kind of Photosynthetically Active Radiation Sensor¶*

Light-emitting diodes (LED), which are designed as quasi-monochromatic light sources, can also function as spectrally selective photodiodes. This provides a new kind of photosynthetically active radiation (PAR) sensor that is inexpensive and has much better stability over time than interference filters used in some PAR sensors. The action spectrum of photosynthesis in green plants has principle peaks in the blue and red regions. LED with response peaks in the UV-A (380 nm) and red (620 nm) regions have been used to measure PAR at or near solar noon in an ongoing study begun on 30 April 1996. The sum of the signals from the two LED is highly correlated with measurements by a calibrated filterless PAR sensor (Apogee QSO; Logan, Utah) from 13 September 1997 to 16 January 2002 (r2= 0.97). The sum of the LED signals is also highly correlated with measurements by a calibrated filter PAR sensor (LI-COR LI-190SA; Lincoln, Nebraska) from 20 April 1998 to 16 January 2002 (r2= 0.97). Thus, pairs of spectrally selective LED can function as PAR detectors in economical PAR radiometers. The separate 380 and 620 nm responses also permit an assessment of the differential impact of aerosol events on blue and red PAR and phototropic radiation.

Further considerations of defocus rangefinders

This article follows a previous one that used a geometrical optics approach to analyse the operation of a defocus rangefinder system. In it, procedures were developed to enable range estimation to be made from width measurements of the blur profile when the temporally incoherent light source on the object was small and of unknown finite width. In this article, it is shown that the same procedures can be used for spatially incoherent monochromatic and quasi-monochromatic light sources in the presence of diffraction provided some constraints are met.

Synthesis of a multiple-peak spatial degree of coherence for imaging through absorbing media

The synthesis of a multiple-peak spatial degree of coherence is demonstrated. This degree of coherence enables us to scan different sample points on different altitudes simultaneously and thus decreases the acquisition time. The multipeak degree of coherence is also used for imaging through an absorbing layer with different thicknesses or different indices of refraction along the layer. All our experiments are performed with a quasi-monochromatic light source. Therefore problems of dispersion and inhomogeneous absorption are avoided. Our experimental results are presented.

Feature Article: Laser-Based Ionization Techniques in Rare Isotope Research: Production, Spectroscopy, and Detection

The interaction of the atomic nucleus and its electromagnetic properties, represented by spin, nuclear moments, and charge radii, with the electronic shell reveals a detailed view into existence, behavior, structure, and stability of nuclear matter in its ground state. Studies along the valley of β-stability of the nuclear chart and particularly far out into the range of unstable short-lived radioactive nuclides are of major interest, for example, for the development of corresponding models. In parallel, optical techniques developed in this context have found widespread applications also for analytics of rare isotopes. Almost immediately after the development of tunable lasers as strong and quasi-monochromatic light source around the year 1960, laser spectroscopic techniques have emerged and found broad acceptance in this field, where they revolutionized and almost completely replaced the former methods of classical optical spectroscopy.

A 5-year study of a new kind of photosynthetically active radiation sensor.

Light-emitting diodes (LED), which are designed as quasi-monochromatic light sources, can also function as spectrally selective photodiodes. This provides a new kind of photosynthetically active radiation (PAR) sensor that is inexpensive and has much better stability over time than interference filters used in some PAR sensors. The action spectrum of photosynthesis in green plants has principle peaks in the blue and red regions. LED with response peaks in the UV-A (380 nm) and red (620 nm) regions have been used to measure PAR at or near solar noon in an ongoing study begun on 30 April 1996. The sum of the signals from the two LED is highly correlated with measurements by a calibrated filterless PAR sensor (Apogee QSO; Logan, Utah) from 13 September 1997 to 16 January 2002 (r2 = 0.97). The sum of the LED signals is also highly correlated with measurements by a calibrated filter PAR sensor (LI-COR LI-190SA; Lincoln, Nebraska) from 20 April 1998 to 16 January 2002 (r2 = 0.97). Thus, pairs of spectrally selective LED can function as PAR detectors in economical PAR radiometers. The separate 380 and 620 nm responses also permit an assessment of the differential impact of aerosol events on blue and red PAR and phototropic radiation.