Chromatic Effects Research Articles

Analysis of the chromatic dispersion effect on the subcarrier wave QKD system.

In this paper we investigate the chromatic dispersion impact on the quantum key distribution system based on multi-mode weak coherent phase-coded states. We provide an asymptotic secure key rate estimation, taking into account error detection probability due to chromatic dispersion. We demonstrate numerically and experimentally that the effect of chromatic dispersion in an optical fiber without any compensation hinders the secret key distribution at a distance more than 53 km. Finally, we propose a modification to the considered quantum communication system in order to mitigate the influence of chromatic dispersion on its performance.

Correcting for chromatic stellar activity effects in transits with multiband photometric monitoring: application to WASP-52

Context.The properties, distribution, and evolution of inhomogeneities on the surface of active stars, such as dark spots and bright faculae, significantly influence the determination of the parameters of an orbiting exoplanet. The chromatic effect they have on transmission spectroscopy, for example, could affect the analysis of data from future space missions such asJames WebbSpace Telescope and Ariel.Aims.To quantify and mitigate the effects of those surface phenomena, we developed a modelling approach to derive the surface distribution and properties of active regions by modelling simultaneous multi-wavelength time-series observables.Methods.We present an upgraded version of theStarSimcode, now featuring the capability to solve the inverse problem and derive the properties of the stars and their active regions by modelling time-series data. As a test case, we analyse ~600 days ofBV RImultiband photometry from the 0.8-mJoan Oró(TJO) and 1.2-m STELLA telescopes of the K2 V exoplanet host star WASP-52. From the results, we further simulated the chromatic contribution of surface phenomena on the observables of its transiting planet.Results.UsingStarSimwe are able to determine the relevant activity parameters of WASP-52 and reconstruct the time-evolving longitudinal map of active regions. The star shows a heterogeneous surface composed of dark spots with a mean temperature of 575 ± 150 K lower than the photospheric value, with filling factors ranging from 3 to 14%. We used the results to study the chromatic effects on the depths of exoplanet transits obtained at different epochs and corresponding to different stellar spot distributions. In the case of WASP-52, which has peak-to-peak photometric variations of ~7% in the visible, the residual effects of dark spots on the measured transit depth of its giant planet, after applying the calculated corrections, are about 10−4at 550 nm and 3 × 10−5at 6μm.Conclusions.We demonstrate that by using contemporaneous ground-based multiband photometry of an active star, it is possible to reconstruct the parameters and distribution of active regions over time, thus making it feasible to quantify the chromatic effects on the planetary radii measured with transit spectroscopy and mitigate them by about an order of magnitude.

VISUAL FUNCTIONS AFTER IMPLANTATION OF ACRYSOF MONOFOCAL INTRAOCULAR LENSES.

The purpose of the study was to evaluate the visual functions after implantation of Acrysof monofocal intraocular lenses Alcon (SA60AT. MA50BM a SN60WF a SN6AT). Four works are presented in the overview. The first work deals with the effect of eye length. corneal optic power and anterior chamber depth on the uncorrected near visual acuity (UNVA) after IOL implantation. The second work compares the effect of eye position (horizontal and vertical) on the final UNVA. The third work deals with the influence of the spherical lenses (SA and MA) and yellow aspherical lenses (SN) on UNVA. The later work examines the effect of pupil width on UNVA. Results: The first work showed the dependence of eye axial length (the largest in eyes bellow 22.5 mm. r=0.36) on UNVA. 77.4 % of eyes with axial length below 22.5 mm had UNVA better than 0.5 and 70.49 % of all evaluated eyes had UNVA better than 0.5. Uncorrected far visual acuity (UDVA) better than 1.0 was in 97.54 % eyes in the whole group. In the second work we found a mean correlation in eyes shorter than 22.5 mm with UNVA in horizontal position (r=0.39) and in the vertical position (r=0.49). UNVA improved in these eyes inhorizontal position from 0.53 to 0.58 in vertical position of the eye. In all eyes from the group UNVA changed from0.51 to 0.56. The third work demonstrated the effect of sphericity and chromaticity on UNVA. Better than 0.5 in the group of eyes shorter than 22.5 mm in SA IOL in 67 % and in SN IOL in 60 %. In eyes with mean axial length was UNVA better than 0.5 in SA IOL in 86.5 %. in MA IOL in 81 % and in SN IOL in 75 %. In eyes longer than 23.5 mm was UNVA better than 0.5 in SA IOL in 100 % of eyes, in MA IOL in 60 % and in SN IOL in 33 % of eyes. In the fourth work the effect of pupil size was not demonstrated. The works showed excellent results of UNVA and UDVA after implantation of Acrysof monofocal lenses.

Numerical modelling of chromatic effects on axicon-focused beams used to generate HOFI plasma channels

Hydrodynamic optical-field-ionised (HOFI) plasma channels promise a route towards high repetition-rate, metre-scale stages for future laser plasma accelerators. These channels are formed by hydrodynamic expansion of a plasma column produced by optical field ionisation at the focus of a laser, typically from an axicon lens. Since the laser pulses used to generate the initial plasma column are of sub-picosecond duration, chromatic effects in the axicon lens could be important. In this paper we assess these effects using a numerical propagation code. The code is validated using analytical formulae and experimental data. For the parameter range investigated, dispersive effects are found to be of minor importance, reducing the peak on-axis intensity in the focal region by approximately 10%.

Facile synthesis of nanostructured cobalt pigments by Co- A zeolite thermal conversion and its application in porcelain manufacture

An innovative and facile synthesis of cobalt based inorganic pigment was carried out by means of a low energy thermal conversion of a cobalt-exchanged zeolite. The Na-A [LTA] zeolite was used, since it is a low cost and easily available raw material. The ion exchange mechanism allowed to control, at microscopic level, the composition of the zeolitic precursor. Several chromatic effects could be obtained by varying the treatment temperature and/or the cobalt concentration in the contact solution. The reliability of these new zeolite-based pigments was tested in porcelain manufacture, in collaboration with the Institute for the Capodimonte porcelain “Giovanni Caselli”. The developed cobalt pigments were successfully tested either in the porcelain mixture to obtain a coloured product or in the decoration step (such as ingobbio, colored glazes and “third fire decoration”).

Performance limits of adaptive-optics/high-contrast imagers with pyramid wavefront sensors

ABSTRACT Advanced adaptive-optics (AO) systems will likely utilize pyramid wavefront sensors (PWFSs) over the traditional Shack–Hartmann sensor in the quest for increased sensitivity, peak performance and ultimate contrast. Here, we explain and quantify the PWFS theoretical limits as a means to highlight its properties and applications. We explore forward models for the PWFS in the spatial-frequency domain: these prove useful because (i) they emanate directly from physical-optics (Fourier) diffraction theory; (ii) they provide a straightforward path to meaningful error breakdowns; (iii) they allow for reconstruction algorithms with $O (n\, \log(n))$ complexity for large-scale systems; and (iv) they tie in seamlessly with decoupled (distributed) optimal predictive dynamic control for performance and contrast optimization. All these aspects are dealt with here. We focus on recent analytical PWFS developments and demonstrate the performance using both analytic and end-to-end simulations. We anchor our estimates on observed on-sky contrast on existing systems, and then show very good agreement between analytical and Monte Carlo performance estimates on AO systems featuring the PWFS. For a potential upgrade of existing high-contrast imagers on 10-m-class telescopes with visible or near-infrared PWFSs, we show, under median conditions at Paranal, a contrast improvement (limited by chromatic and scintillation effects) of 2×–5× when just replacing the wavefront sensor at large separations close to the AO control radius where aliasing dominates, and of factors in excess of 10× by coupling distributed control with the PWFS over most of the AO control region, from small separations starting with an inner working angle of typically 1–2 λ/D to the AO correction edge (here 20 λ/D).

Quantifying EoR delay spectrum contamination from diffuse radio emission

ABSTRACT The 21 cm hyperfine transition of neutral hydrogen offers a promising probe of the large-scale structure of the universe before and during the Epoch of Reionization (EoR), when the first ionizing sources formed. Bright radio emission from foreground sources remains the biggest obstacle to detecting the faint 21 cm signal. However, the expected smoothness of foreground power leaves a clean window in Fourier space where the EoR signal can potentially be seen over thermal noise. Though the boundary of this window is well defined in principle, spectral structure in foreground sources, instrumental chromaticity, and choice of spectral weighting in analysis all affect how much foreground power spills over into the EoR window. In this paper, we run a suite of numerical simulations of wide-field visibility measurements, with a variety of diffuse foreground models and instrument configurations, and measure the extent of contaminated Fourier modes in the EoR window using a delay-transform approach to estimate power spectra. We also test these effects with a model of the Hydrogen Epoch of Reionization Array (HERA) antenna beam generated from electromagnetic simulations, to take into account further chromatic effects in the real instrument. We find that foreground power spillover is dominated by the so-called pitchfork effect, in which diffuse foreground power is brightened near the horizon due to the shortening of baselines. As a result, the extent of contaminated modes in the EoR window is largely constant over time, except when the Galaxy is near the pointing centre.

Design of diffractive lenses operating at several wavelengths.

We propose a method for designing diffractive lenses having a fixed-position focus at several prescribed wavelengths, which we refer to as spectral diffractive lenses (SDLs). The method is based on minimizing an objective function describing the deviation of the complex transmission functions of the spectral lens at the operating wavelengths from the complex transmission functions of diffractive lenses calculated separately for each of these wavelengths. As examples, SDLs operating at three, five, and seven different wavelengths are designed. The simulation results of the calculated lenses confirm high efficiency of the proposed method. For experimental verification of the design method, we fabricate using direct laser writing and experimentally investigate an SDL operating at five wavelengths. The presented experimental results confirm the efficiency of the proposed method in practical problems of designing SDLs. The obtained results may find applications in the design and fabrication of novel flat diffractive lenses with reduced chromatic effects.

Main Factors Affecting the Photographic Determination of the Turbidity and Chromaticity of Water

The main factors that affect the performance characteristics of determining the turbidity and chromaticity of water by digital colorimetry in field (on-site) are studied. The test samples are suspensions of formazine and solutions composing the dichromate–cobalt chromaticity scale, which are used for calibration in standardized spectrophotometric methods for monitoring water quality. The affecting factors include the geometry of the vessel for colorimetric samples, the manufacturing quality of the adjustment device (drawing of chess fields), the method of fixing the camera in shooting, the method of performing the blank experiment, the illumination of the sample in shooting, the degree of cropping of the edges of the photograph of the chess fields in its digital processing, camera specifications, and the mutual effect of chromaticity and turbidity on the contrast of the photograph and its mean-root-square brightness. It is demonstrated that for the design of the on-site photographic measurements it is enough to have a digital camera, an adjustment device, and a measuring vessel. Photographing can be done with a camera held in hands. An empty measuring vessel may be used as an optically transparent sample for the blank experiment. Recommendations have been developed on optimizing the photographic measurements of turbidity and chromaticity. A possibility of the simultaneous determination of turbidity and chromaticity is shown by the example of monitoring the quality of tap water.

Grouping ambiguous neural representations: neither identical chromaticity (the stimulus) nor color (the percept) is necessary.

Multiple regions, each with the same ambiguous chromatic neural representation, are resolved to have the identical perceived color more often than chance [Proc. Natl. Acad. Sci. USA93, 15508 (1996)PNASA60027-842410.1073/pnas.93.26.15508; J. Opt. Soc. Am. A35, B85 (2018)JOAOD60740-323210.1364/JOSAA.35.000B85]. This reveals that the regions are grouped, but it is unclear whether they are grouped because each one has the identical competing representations of the same stimuli (that is, the same chromaticities) or, alternatively, identical competing representations of the same colors one sees. The current study uses chromatic induction, as in Nat. Neurosci.6, 801 (2003)NANEFN1097-625610.1038/nn1099, to disentangle whether grouping depends on identical (though ambiguous) stimulus chromaticities or on perceived colors, by (1) inducing one chromaticity to appear in two different colors or (2) inducing two different chromaticities to appear in the same color. All stimuli were equiluminant gratings with chromatic inducing and test fields. Three observers were tested, first completing color matches to measure induced color-appearance shifts and second completing grouping measurements using interocular-switch rivalry, a method with rivalrous dichoptic images swapped between the eyes at 3.75 Hz [J. Vis.17, 9 (2017)1534-736210.1167/17.5.9]. Each of two separate areas, one above and one below fixation, had dichoptic rivalry. The two sets of regions had either identical or different chromaticities that could appear either as the same color or not. Observers reported their percepts when both areas above and below fixation were grouped by color or by chromaticity (or neither in an additional experimental condition). All conditions showed significant groupings for every observer, including when neither color nor chromaticity was identical in a "group." Moreover, there was never a significant effect of chromaticity versus color for any observer. This is the result expected if neither color nor chromaticity must match between two regions in order for them to be grouped and suggests that, instead, some other feature drives grouping.

COXINEL transport of laser plasma accelerated electrons

Laser plasma acceleration (LPA) enables the generation of an up to several GeV electron beam with a short bunch length and high peak current within a centimeter scale. In view of undulator type light source applications, electron beam manipulation has to be applied. We report here on detailed electron beam transport for an LPA electron beam on the COXINEL test line, that consists of strong permanent quadrupoles to handle the electron beam divergence, a magnetic chicane to reduce the energy spread and a second set of quadrupoles for adjusting the focusing inside the undulator. After describing the measured LPA characteristics, we show that we can properly transport the electron beam along the line, thanks to several screens. We also illustrate the influence of the chromatic effects induced by the electron beam energy spread, both experimentally and numerically. We then study the sensitivity of the transport to the electron beam pointing and skewed quadrupolar components.

An RDE Approach to Investigate the Influence of Chromate on the Cathodic Kinetics on 7XXX Series Al Alloys under Simulated Thin Film Electrolytes

The effect of sodium chromate on the cathodic current availability pertinent to the micro-galvanic-induced corrosion of high-strength AA7XXX alloys under simulated thin electrolyte films representative of atmospheric conditions was investigated utilizing a combination of electrochemical and surface characterization techniques. The rotating disk electrode technique provided a means to simulate the effects of water layer thickness to differentiate thin film conditions from full immersion conditions, and enabled the study of the mass-transport-limited oxygen reduction reaction (ORR) on AA7XXX alloys as a function of chromate concentration. The ORR current density decreased by up to two orders of magnitude upon addition of 10 mM chromate, however, the degree of inhibition was observed to depend on the Cu content of the alloy. Chromate was reduced irreversibly to form a Cr3+-rich film on the alloy surface that blocked cathodic sites and hindered ORR. This film was confirmed by X-ray photoelectron spectroscopic characterization of the chemistry and thickness of the chromate-induced layer formed on the specimens after exposure to chromate. The layer was approximately 13 nm in thickness and consisted of mixed Cr3+/Cr6+ oxides with some metallic Cr. Studies on a Pt electrode demonstrated the intrinsic ability of chromate as an effective inhibitor for ORR.

The Effect of Riboflavin Concentration, Antioxidant Activity, and Chromaticity on Craft Beer Photooxidation

The Effect of Riboflavin Concentration, Antioxidant Activity, and Chromaticity on Craft Beer Photooxidation

Electron Beam Brightness and Undulator Radiation Brilliance for a Laser Plasma Acceleration Based Free Electron Laser

We report here on spontaneous undulator radiation and free electron laser calculations after a 10-m long transport line (COXINEL) using a Laser Plasma acceleration (LPA) source. The line enables the manipulation of the properties of the produced electron beams (energy spread, divergence, dispersion) in view of light source applications. The electron beam brightness and undulator radiation brilliance are addressed by an analytical approach enabling us to point out the influence of chromatic effects in the COXINEL case.

Nanochromates MCr2O4 (M = Co, Ni, Cu, Zn): Preparation, Characterization, and Catalytic Activity on the Thermal Decomposition of Fine AP and CL-20.

The chromate nanoparticles such as CoCr2O4, NiCr2O4, CuCr2O4, and ZnCr2O4 were prepared by a modified sol–gel method. The structural and morphological properties of the chromate nanoparticles were characterized by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The catalytic effects of chromates on the thermal decomposition of fine ammonium perchlorate (FAP) and hexanitrohexaazaisowurtzitane (CL-20) were studied by the TG-DTG measurements. Results show that the addition of CoCr2O4, NiCr2O4, CuCr2O4, and ZnCr2O4 nanoparticles makes the activation energies for the thermal decomposition of FAP decrease by 93.9, 94.0, 83.1, and 67.0 kJ·mol–1, and the thermal decomposition temperatures decrease by 45.0, 24.9, 57.7, and 38.8 K respectively. On the other hand, a similar trend exists in the case of the thermal decomposition of CL-20. Therefore, the addition of nanochromates shows high catalytic efficiency on the thermal decomposition of both FAP and CL-20 components, which would be beneficial to promote the burning rate of propellants containing FAP and CL-20 components.

Digital fronthaul link based on optimised digital radio over fibre system

The high optical bandwidth requirement in the mobile fronthaul link of the next generation cloud radio access network represents one of the major design constraints. In this study, a digital fronthaul link based on digital radio over fibre system that integrates the duobinary coding scheme with the optical single sideband (OSSB) transmission is proposed. This system reduces the spectral occupancy of the transmitted signals as well as the chromatic dispersion effects induced by fibre in both the electrical and optical domains. The OSSB signal is created by driving two cascaded optical modulators with a combination of a baseband digital signal and the Hilbert transform of that signal. The transmission performance of a digitised 16-quadrature amplitude modulation 16-QAM radio frequency signal with a bit rate of 1.25 Gb/s over a standard single mode fibre is investigated. The results show that the fronthaul transmission length can be extended by 75 and 16.6% relative to the case of transmitting the digitised signal using double sideband and single sideband (SSB) transmission formats, respectively. The power budget is improved by 10 dB compared to the SSB case with respect to the measured optical signal-to-noise ratio at 70 km fibre distance, while maintaining the EVM below the standardised values of the 3GPP.

Extreme Learning Machines to Combat Phase Noise in RoF-OFDM Schemes

Radio-over-fiber (RoF) orthogonal frequency division multiplexing (OFDM) systems have been revealed as the solution to support secure, cost-effective, and high-capacity wireless access for the future telecommunication systems. Unfortunately, the bandwidth-distance product in these schemes is mainly limited by phase noise that comes from the laser linewidth, as well as the chromatic fiber dispersion. On the other hand, the single-hidden layer feedforward neural network subject to the extreme learning machine (ELM) algorithm has been widely studied in regression and classification problems for different research fields, because of its good generalization performance and extremely fast learning speed. In this work, ELMs in the real and complex domains for direct-detection OFDM-based RoF schemes are proposed for the first time. These artificial neural networks are based on the use of pilot subcarriers as training samples and data subcarriers as testing samples, and consequently, their learning stages occur in real-time without decreasing the effective transmission rate. Regarding the feasible pilot-assisted equalization method, the effectiveness and simplicity of the ELM algorithm in the complex domain are highlighted by evaluation of a QPSK-OFDM signal over an additive white Gaussian noise channel at diverse laser linewidths and chromatic fiber dispersion effects and taking into account several OFDM symbol periods. Considering diverse relationships between the fiber transmission distance and the radio frequency (for practical design purposes) and the duration of a single OFDM symbol equal to 64 ns, the fully-complex ELM followed by the real ELM outperform the pilot-based correction channel in terms of the system performance tolerance against the signal-to-noise ratio and the laser linewidth.

The Measured Impact of Chromatic Atmospheric Effects on Barycentric Corrections: Results from the EXtreme PREcision Spectrograph

Abstract One source of error in high-precision radial velocity measurements of exoplanet host stars is chromatic change in Earth’s atmospheric transmission during observations. Mitigation of this error requires that the photon-weighted barycentric correction be applied as a function of wavelength across the stellar spectrum. We have designed a system for chromatic photon-weighted barycentric corrections with the EXtreme PREcision Spectrograph and present results from the first year of operations, based on radial velocity measurements of more than 103 high-resolution stellar spectra. For observation times longer than 250 s, we find that if the chromatic component of the barycentric corrections is ignored, a range of radial velocity errors up to 1 m s−1 can be incurred with cross-correlation, depending on the nightly atmospheric conditions. For this distribution of errors, the standard deviation is 8.4 cm s−1 for G-type stars, 8.5 cm s−1 for K-type stars, and 2.1 cm s−1 for M-type stars. This error is reduced to well-below the instrumental and photon-noise limited floor by frequent flux sampling of the observed star with a low-resolution exposure meter spectrograph.

Skew Quadrupole Effect of Laser Plasma Electron Beam Transport

Laser plasma acceleration (LPA) capable of providing femtosecond and GeV electron beams in cm scale distances brings a high interest for different applications, such as free electron laser and future colliders. Nevertheless, LPA high divergence and energy spread require an initial strong focus to mitigate the chromatic effects. The reliability, in particular with the pointing fluctuations, sets a real challenge for the control of the dispersion along the electron beam transport. We examine here how the magnetic defects of the first strong quadrupoles, in particular, the skew terms, can affect the brightness of the transported electron beam, in the case of the COXINEL transport line, designed for manipulating the electron beam properties for a free electron laser application. We also show that the higher the initial beam divergence, the larger the degradation. Experimentally, after having implemented a beam pointing alignment compensation method enabling us to adjust the position and dispersion independently, we demonstrate that the presence of non-negligible skew quadrupolar components induces a transversal spread and tilt of the beam, leading to an emittance growth and brightness reduction. We are able to reproduce the measurements with beam transport simulations using the measured electron beam parameters.

Chromate Effect on Iodate Incorporation into Calcite

Incorporation of iodate into calcite (CaCO3) may be used as an in situ treatment strategy for radioiodine in contaminated soils and groundwater, but the presence of other contaminants may inhibit its efficiency. To this end, the potential for chromate to interfere with iodate incorporation into CaCO3 was investigated as an example of how co-located contaminants may impact in situ remediation efficacy. Here, batch precipitation experiments were periodically sub-sampled over 21 days to determine the kinetic effects of chromate on iodate removal and incorporation into calcite. From these experiments, a decrease in iodate removal from >60 to <40% was observed upon chromate addition (1–112 ppm of chromate) and ≤11% of chromate was removed with a minor dependence upon the initial chromate concentration. Analysis of the solid phase using extended X-ray absorption fine structure (EXAFS) spectroscopy informed by ab initio molecular dynamics simulations revealed that the iodate incorporation mode remains unchanged ...