Spectral Intensity Distribution Research Articles

In-house energy resolved Laue XRD measurements with a Pilatus detector

The use of 2D position and energy sensitive hybrid pixel Pilatus detectors allows performing energy-dispersive analysis of Bragg reflections [1]. This significantly improves the classical Laue experiments enabling the unique determination of the crystal lattice and resolving the higher order harmonics. It allows quantitative crystal structure determination using the Laue method without having any priory information about the crystal [2]. Such energy-dispersive Laue diffraction (EDLD) experiments can be performed with a white X-ray beam either from a synchrotron source or from conventional X-ray tubes. The second approach looks less profitable due to its lower irradiation intensity, but this can be compensated considering the better control of white beam spectra by applying different voltage/current settings during the tube operation. Thus, one can efficiently combine the primary beam and XRD measurements using the same Pilatus detector. This allows the implementation of the energy resolved (color Laue) method for any conventional XRD diffractometer equipped with a Pilatus detection system. In the present work EDLD experiments with a conventional X-ray tube were combined with corresponding primary beam measurements using a 300K Pilatus detector tuned for operation within an energy range of 4-25 keV at energy resolution <0.12 keV. Such a combination simplifies several data correction procedures (the spectral intensity distribution, the sample absorption etc.) significantly. Following our developed intensity correction protocols the structure refinement of a reference quartz sample could be achieved with R-factor <0.10. Possible applications of this method (e.g. quantitative XRD studies with stationary crystals) and the details for its further development will be discussed.

Determination of true temperature of opaque materials via spectral distribution of thermal radiation intensity: application of Wien’s displacement law

The equation for the derivative connecting surface spectral emissivity, wavelength, and thermodynamic (true) temperature of an opaque heated body at the point of spectral maximum of thermal radiation was obtained. It is suggested to solve the problem of determining the true temperature of an opaque surface in two stages. At the first stage, the spectral range, most comfortable for approximation of body emissivity, is distinguished using a special function (relative emissivity), and the true temperature is determined. At the second stage, the true temperature is determined again using the resulting equation for the derivative. The dimensionless parameter that connects the radiative properties of material with the peak wavelength and characterizes deviation from Wien’s displacement law was found. If the absolute value of this parameter is low, the value of true temperature obtained at the first step can be specified at the second stage. This approach is illustrated by experimental data obtained at comparison of spectral radiance of the temperature lamps.

Empirical model of variations in the continuum emission in the upper atmosphere. 1. Intensity

The ground-based and satellite measurements of the upper-atmosphere continuum (continuous emission) intensity in the visible and near IR spectral regions have been analyzed. The data were obtained at the geophysical stations, located in different regions of the globe, and at Mir Space Station. The regularities in the spectral distribution of the continuum emission intensity and emission variations have been revealed for different heliogeophysical conditions.

Filtering chromatic aberration for wide acceptance angle electrostatic lenses.

Chromatic aberration is a major issue for imaging mainly with large acceptance angle electrostatic lenses. Its correction is necessary to take advantage of the outstanding spatial and angular resolution that these lenses provide. We propose a method to eliminate the effect of chromatic aberration on the measured images by determining the impact resulting from higher and lower kinetic energies. Based on a spectral image sequence and a matrix, which describes the transmission function of the lens, a system of linear equations is solved to approximate the 2D spectral intensity distribution of the sample surface. We present the description of our method and preliminary test results, which show significant contrast and image quality improvement. The presented algorithm can also be applied as a software-based energy analyzer.

Spectral transformation of infrared ultrashort pulses in laser crystals

The impact of peculiarities of transparent media on the self transformation of femtosecond pulses is considered. Spectral width and intensity distribution of anti-Stokes part of supercontinuum generated by infrared femtosecond pulses in selected single crystals were determined for different pulse energy density as a function of incident pulse wavelength changed in the 800–1600nm region. Effect of material bandgap on the supercontinuum generation was examined based on experimental data for single crystals of gadolinium orthosilicate, gallium gadolinium garnet, lithium tantalate and lutetium vanadate. It was found that the anti-Stokes part of supercontinuum generated in Gd2SiO5 and Gd3Ga5O12 crystals has a quite large spectral width with a short wavelength cut-off around 450nm and contains a broad plateau.

MOMENTUM RESOLVED RADIO FREQUENCY SPECTROSCOPY OF A UNITARY FERMI GAS WITH EXTENDED GMB APPROXIMATION

In this paper, the momentum-resolved radio-frequency spectra of a unitary Fermi gas in the normal phase are presented and analyzed on the basis of the framework of the non-self-consistent T-matrix approximation with the extended Gorkov and Melik-Barkhudarov (GMB) approximation. We report the calculated occupied spectral intensity and energy distribution curves for different temperatures above T c . Our results indicate the existence of pseudogap phenomenon which would be helpful for further understanding of the pseudogap in high-temperature superconductivity.

Diagnostics of First Wall Materials in a Magnetically Confined Fusion Device by Polarization-Resolved Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a powerful analytical tool for real-time diagnostics and detection of multiple elements deposited at the first wall of magnetically confined plasma fusion devices. Recently, we have tested LIBS in our laboratory for application to in situ real-time diagnostics in the fusion device EAST. In this study, we applied polarization-resolved LIBS (PR-LIBS) to reduce the background continuum and enhance the resolution and sensitivity of LIBS. We used aluminium (Al) (as a substitute for Be) and the first wall materials tungsten (W) and molybdenum (Mo) to investigate polarized continuum emission and signal-to-background ratio (SBR). A Nd:YAG laser with first, second and third harmonics was used to produce plasma. The effects of the laser polarization plane, environmental pressure and polarizer detection angle were investigated. The spectra obtained without using a polarizer (i.e. LIBS) were compared with those obtained with a polarizer (PR-LIBS). Distribution of emission spectral intensity was observed to follow Malus' law with respect to variation in the angle of detection of the polarizer. The spectra obtained by PR-LIBS had a higher SBR and greater stability than those obtained by LIBS, thereby enhancing the reliability of LIBS for quantitative analyses. A comparison of Al, Mo and W showed that W exhibited a higher continuum with stronger polarization than the low-Z elements.

Two-dimensional codistribution spectroscopy to determine the sequential order of distributed presence of species

Two-dimensional codistribution spectroscopy (2DCDS), a technique designed specifically for the analysis of population dynamics, such as temporal distributions of species during a chemical reaction, is described. 2D codistribution analysis focus on the signal features reflecting the distributed presence of species, instead of the variation patterns of perturbation-induced deviations from the reference state, which has been traditionally analyzed by two-dimensional correlation spectroscopy (2DCOS). This technique is derived from the moment analysis of spectral intensity distributions along the perturbation variable axis within a well-defined observation interval. Derivation and properties of 2D codistribution spectra are provided, and comparison is made to 2D correlation spectroscopy with the help of simulated IR spectra generated from model chemical reactions.

Reflection-based fibre-optic refractive index sensor using surface plasmon resonance

A reflection-based fibre-optic refractive index sensor using surface plasmon resonance (SPR) in a thin metal film sputtered on a bare core of a multimode optical fibre is presented. The sensing element of the SPR fibre-optic sensor is the core of a step-index optical fibre made of fused silica with a gold film double-sided sputtered on the whole core surface, including the core end face. Consequently, a terminated reflection-based sensing scheme to measure the refractive indices of liquids is realized. The sensing scheme uses a wavelength interrogation method and the refractive index of a liquid is sensed by measuring the position of the dip in the reflected spectral intensity distribution. As an example, the aqueous solutions of ethanol with refractive indices in a range from 1.333 to 1.363 are measured. In addition, the increase in the sensitivity of the SPR fibre-optic refractive index sensor with the decrease of the fibre sensing length is demonstrated.

Night sky luminance under clear sky conditions: Theory vs. experiment

Sky glow is caused by both natural phenomena and factors of anthropogenic origin, and of the latter ground-based light sources are the most important contributors for they emit the spatially linked spectral radiant intensity distribution of artificial light sources, which are further modulated by local atmospheric optics and perceived as the diffuse light of a night sky. In other words, sky glow is closely related to a city's shape and pattern of luminaire distribution, in practical effect an almost arbitrary deployment of random orientation of heterogeneous electrical light sources. Thus the luminance gradation function measured in a suburban zone or near the edges of a city is linked to the City Pattern or vice versa.It is shown that clear sky luminance/radiance data recorded in an urban area can be used to retrieve the bulk luminous/radiant intensity distribution if some a-priori information on atmospheric aerosols is available. For instance, the single scattering albedo of aerosol particles is required under low turbidity conditions, as demonstrated on a targeted experiment in the city of Frýdek-Mistek. One of the main advantages of the retrieval method presented in this paper is that the single scattering approximation is satisfactorily accurate in characterizing the light field near the ground because the dominant contribution to the sky glow has originated from beams propagated along short optical paths.

Field survey around strong motion stations and its implications on the seismic intensity in the Lushan earthquake on April 20, 2013

The Ms7.0 Lushan earthquake on April 20, 2013 is another destructive event in China since the Ms8.0 Wenchuan earthquake in 2008 and Ms7.1 Yushu earthquake in 2010. A large number of strong motion recordings were accumulated by the National Strong Motion Observation Network System of China. The maximum peak ground acceleration (PGA) at Station 51BXD in Baoxing Country is recorded as −1,005.3 cm/s2, which is even larger than the maximum one in the Wenchuan earthquake. A field survey around three typical strong motion stations confirms that the earthquake damage is consistent with the issued map of macroseismic intensity. For the oscillation period 0.3–1.0 s which is the common natural period range of the Chinese civil building, a comparison shows that the observed response spectrums are considerably smaller than the designed values in the Chinese code and this could be one of the reasons that the macroseismic intensity is lower than what we expected despite the high amplitude of PGAs. The Housner spectral intensities from 16 stations are also basically correlated with their macroseismic intensities, and the empirical distribution of spectral intensities from Lushan and Wenchuan Earthquakes under the Chinese scale is almost identical with those under the European scale.

Strong-field spectral interferometry using the carrier–envelope phase

The carrier–envelope phase (CEP) of ultrashort laser pulses is an important parameter in strong-field physics that controls temporally localized events on a sub-cycle timescale. The relative timing of these events is directly encoded into the measured spectral intensity distribution, and can be accessed by the use of spectral interferometry. Here, we combine this analysis with CEP control in a two-dimensional way, creating a novel spectroscopic method to explore the temporal dynamics of strong-field processes. We apply this general method to CEP-dependent high-harmonic generation and find that contributions of three different sub-cycle electron quantum paths can be separated, allowing one to quantify the dipole-phase dependence on the CEP in the non-adiabatic regime. The CEP-dependent time delay between two full-cycle spaced attosecond pulses was determined to modulate by 54 ± 16 as. We confirm the generality of the method by further applying it to CEP-dependent photoemission from a nanoscale metal tip.

An optimized photon pair source for quantum circuits

We implement an ultrafast pulsed type-II parametric down conversion source in a periodically poled KTP waveguide at telecommunication wavelengths with almost identical properties between signal and idler. As such, our source resembles closely a pure, genuine single mode photon pair source with indistinguishable modes. We measure the joint spectral intensity distribution and second order correlation functions of the marginal beams and find with both methods very low effective mode numbers corresponding to a Schmidt number below 1.16. We further demonstrate the indistinguishability as well as the purity of signal and idler photons by Hong-Ou-Mandel interferences between signal and idler and between signal/idler and a coherent field, respectively. Without using narrowband spectral filtering, we achieve a visibility for the interference between signal and idler of 94.8% and determine a purity of more than 80% for the heralded single photon states. Moreover, we measure raw heralding efficiencies of 20.5% and 15.5% for the signal and idler beams corresponding to detector-loss corrected values of 80% and 70%.

Effect of different coloured luminous surrounds on LED discomfort glare perception

Recently, there has been increased interest in energy-efficient lighting as energy resources become higher in demand. Anecdotal evidence suggests that certain populations believe light-emitting diodes (LED) produce more glare than traditional technologies. This may be due to a number of factors such as spectral power distribution (SPD), source luminance, or beam intensity distribution. A study was conducted to assess the effect of different SPDs on the perception of discomfort glare from an LED source. For the range of conditions evaluated, the presence of any luminous surround significantly reduced the perception of discomfort glare from the LED array. The blue luminous surround reduced discomfort glare perception significantly less than the white or the yellow luminous surrounds. The implications for solid-state lighting systems are discussed.

Noise Reduction in White Light Lidar Signal Using a One-Dim and Two-Dim Daubechies Wavelet Shrinkage Method

A 1-D and 2-D Daubechies 5 (db5) discrete wavelet shrinkage methods using a 10 level decomposition was applied to white light lidar data particularly at 350 nm and 550 nm backscattered signal. At 350 nm, the backscattered signal is very weak as compared to 550 nm backscattered signal because of the spectral intensity distribution of the generated white light. The 1-D and 2-D wavelet shrinkage method gave a much better result as compared with the moving average method. However, the 2-D wavelet shrinkage method produced a much better denoised lidar signal compared with the 1-D wavelet shrinkage method. This is indicated by the 142% increase in correlation coefficient between the 2-D denoised lidar signal and the 800 nm original lidar signal as compared with only 12% increase in correlation coefficient for the 1-D denoised lidar signal. The 2-D wavelet shrinkage method also gave a much higher SNR value of 65.9 compared to 1-D which is 38.8.

Characteristics of a cylindrical collector mirror for laser-produced xenon plasma soft X-rays and improvement of mirror lifetime by buffer gas

The focusing characteristics of a ruthenium-coated cylindrical mirror were investigated on the basis of its ability to collect and focus broadband 5-17-nm soft X-rays emitted from a laser-produced plasma. Based on the plasmas spectral intensity distribution and the reflectivity function of the mirror, we defined the optimum position of the integrated cylindrical mirror at which the X-ray energy flux transported and focused through the mirror was maximum. A minimum spot diameter of 22 mm at a distance of approximately 200 mm from a soft X-ray source was confirmed. The maximum intensity of the collected soft X-rays was 1.3 mJ/cm(2) at the center of the irradiation zone. Thus, the irradiation intensity was improved by approximately 27 times when compared to that of 47 μJ/cm(2) without the mirror. The debris sputtering rate on the reflection surface of the mirror can be reduced to 1/110 by argon gas at 11 Pa, while the attenuation rate of the soft X-rays due to absorption by the buffer gas can be suppressed to less than 10% at the focal point. The focusing property of the mirror is expected to be maintained for 3000 h or longer without significant degradation for a 100 W/320 pps laser shot if the ruthenium layer is thicker than 10 μm. These results suggest that a stand-alone broadband soft X-ray processing system can be realized by using laser-produced plasma soft X-rays.

Tuning of random lasers by means of external magnetic fields based on the Voigt effect

It has been proposed that emission spectrum of random lasers with magnetically active semiconductor constituents can be made tunable by external magnetic fields. By employing the FDTD method, the spectral intensity and spatial distribution of electric field are calculated in the presence of an external magnetic field. It is numerically shown that due to the magneto-optical Voigt effect, the emission spectrum of a semiconductor-based random laser can be made tunable by adjusting the external magnetic field. The effect of magnetic field on the localization length of the laser modes is investigated. It is also shown that the spatial distribution of electric field exhibited remarkable modification with variation of magnetic field.

Stripe Excitation of High Gain Media With Disorder

We discuss the spatial and spectral intensity distribution of emission in optical gain media under stripe excitation in the case where the intensity reaches saturation level. It is found that modes propagating along the stripe in different directions are spatially separated if they affect each other due to saturation. The investigation includes the effects of wavelength-dependent inhomogenities, such as localized losses and reflective perturbations. Even relatively small distortions of this kind are found to cause considerable spatial and spectral redistribution of the intensity compared to an ideal disorder-free medium. Our results indicate that a simple ansatz may describe some mechanisms that lead to the formation of random laser action that is commonly observed in high gain media, such as organic semiconductors. Furthermore, consequential difficulties of gain measurements in such media using stripe excitation experiments are highlighted.

Angular and spectral radiant intensity distribution of high brightness white LEDs

Angular and spectral radiant intensity distribution of high brightness white LEDs

Spectral intensity distribution of oxygen atom in a plasma plume

Low temperature plasma generated in plasma plume discharge at atmospheric pressure has prosperous application fields in industry because the vacuum device can be dispensable and some complex materials can be treated in three dimensions by this plasma plume. A stable plasma plume was generated in atmospheric pressure air in the present paper by using a plasma needle discharge device. It was found by spectral measurement that there are some spectral lines emitted from oxygen atom such as 777.5 and 844.6 nm in the optical emission spectra of the plasma plume. This phenomenon indicates that oxygen atom with high chemical activity was generated in the air discharge at atmospheric pressure. The spatial distribution of the spectral intensity from the oxygen atom was investigated by spectroscopic method. Results show that the spectral intensity from oxygen atom near the needle electrode was much higher than that in other regions. In order to explain this experimental phenomenon, spatial-resolved signals emitted from the plume were detected by using photomultiplier tubes. It was found that the width of light pulse near the needle electrode was much bigger than that in other regions. These results are important for the application of plasma plume in industry such as sterilization and disinfection fields.