Spectral Nonuniformity Research Articles

Emerging technology for intraoperative margin assessment and post-operative tissue diagnosis for breast-conserving surgery

IntroductionTissue-preserving surgery is utilized progressively in cancer therapy, where a clear surgical margin is critical to avoid cancer recurrence, specifically in breast cancer (BC) surgery. The Intraoperative pathologic approaches that rely on tissue segmenting and staining have been recognized as the ground truth for BC diagnosis. Nevertheless, these methods are constrained by its complication and timewasting for tissue preparation. ObjectiveWe present a non-invasive optical imaging system incorporating a hyperspectral (HS) camera to discriminate between cancerous and non-cancerous tissues in ex-vivo breast specimens, which could be an intraoperative diagnostic technique to aid surgeons during surgery and later a valuable tool to assist pathologists. MethodsWe have established a hyperspectral Imaging (HSI) system comprising a push-broom HS camera at wavelength 380∼1050 nm with source light 390∼980 nm. We have measured the investigated samples' diffuse reflectance (Rd), fixed on slides from 30 distinct patients incorporating mutually normal and ductal carcinoma tissue. The samples were divided into two groups, stained tissues during the surgery (control group) and unstained samples (test group), both captured with the HSI system in the visible and near-infrared (VIS-NIR) range. Then, to address the problem of the spectral nonuniformity of the illumination device and the influence of the dark current, the radiance data were normalized to yield the radiance of the specimen and neutralize the intensity effect to focus on the spectral reflectance shift for each tissue. The selection of the threshold window from the measured Rd is carried out by exploiting the statistical analysis by calculating each region's mean and standard deviation. Afterward, we selected the optimum spectral images from the HS data cube to apply a custom K-means algorithm and contour delineation to identify the regular districts from the BC regions. ResultsWe noticed that the measured spectral Rd for the malignant tissues of the investigated case studies versus the reference source light varies regarding the cancer stage, as sometimes the Rd is higher for the tumor or vice versa for the normal tissue. Later, from the analysis of the whole samples, we found that the most appropriate wavelength for the BC tissues was 447 nm, which was highly reflected versus the normal tissue. However, the most convenient one for the normal tissue was at 545 nm with high reflection versus the BC tissue. Finally, we implement a moving average filter for noise reduction and a custom K-means clustering algorithm on the selected two spectral images (447, 551 nm) to identify the various regions and effectively-identified spectral tissue variations with a sensitivity of 98.95%, and specificity of 98.44%. A pathologist later confirmed these outcomes as the ground truth for the tissue sample investigations. ConclusionsThe proposed system could help the surgeon and the pathologist identify the cancerous tissue margins from the non-cancerous tissue with a non-invasive, rapid, and minimum time method achieving high sensitivity up to 98.95%.

On-chip scalable highly pure and indistinguishable single-photon sources in ordered arrays: Path to quantum optical circuits.

Realization of quantum optical circuits is at the heart of quantum photonic information processing. A long-standing obstacle, however, has been the absence of a suitable platform of single photon sources (SPSs). Such SPSs need to be in spatially ordered arrays and produce, on-demand, highly pure, and indistinguishable single photons with sufficiently uniform emission characteristics to enable controlled interference between photons from distinct sources underpinning functional quantum optical networks. We report on such a platform of SPSs based on a unique class of epitaxial quantum dots dubbed mesa-top single quantum dot. Under resonant excitation, the spatially ordered SPSs (without Purcell enhancement) show single photon purity of >99% [g(2)(0) ~ 0.015], high two-photon Hong-Ou-Mandel interference visibilities of 0.82 ± 0.03 (at 11.5 kelvin, without cavity), and spectral nonuniformity of <3 nanometers, within established locally tunable technology. Our platform of SPSs paves the path to creating on-chip scalable quantum photonic networks for communication, computation, simulation, sensing and imaging.

Full-aperture chirped-pulse grating compression with a non-uniform beam

A novel chirped-pulse compression scheme is proposed to pursue higher pulse peak power of chirped-pulse amplifiers based on state-of-the-art gratings. It is characterized by the spectral non-uniformity of the beam cross section as well as by the uniform size of the beam projections on the four compression gratings. The spatial distribution of spectra is well designed so that the beam can remain generally collimated in the compressor and the gratings can be employed with a full work area. The maximum possible output pulse energy can therefore be increased within the damage threshold limit. A detailed design is developed for a scheduled 50-PW optical parametric chirped-pulse amplifier. Results of the numerical simulation on the focused output show that the spot size and pulse duration in the focal plane are close to those of conventional grating compression. Further, it is a promising method for upgrading existing chirped-pulse amplifiers.

Experimental characterisation of irradiance and spectral non-uniformity and its impact on multi-junction solar cells: Refractive vs. reflective optics

The impact of non-uniform illumination on triple junction solar cells equipped with either refractive or reflective optics without secondary optical elements is characterised by varying the concentrator-to-receiver distance. Indoor experiments covering both electrical measurements and photographs with a charge-coupled device camera are performed. The non-uniformities are examined by differentiating two spectral bands, those affecting the top and middle subcells. This allows the irradiance and spectral distributions to be analysed. The analysis is complemented with ray tracing simulations. Results show a different behaviour for the refractive and reflective systems. Irradiance non-uniformities in the case of the reflective system around the on-focus position are higher than those measured in the refractive system. However, the spectral non-uniformities that characterise the refractive system constitute only a residual effect in the reflective system. The drop in the solar cell fill factor caused by non-uniformities is mainly driven by the degradation of the slope of the I–V curve near the short-circuit point in the case of the refractive system, while it is mainly driven by the degradation of the slope of the I–V curve near the open-circuit point in the case of the reflective system. Both systems are very sensitive to the concentrator-to-receiver distance, a critical parameter that must be accurately designed in any concentrator system. The findings will allow the trade-off between increasing performance and increasing cost strategies to mitigate the non-uniformities in concentrator photovoltaic systems to be better evaluated.

Strongly enhanced infrared emission of a black coating doped with multiwall carbon nanotubes

Advanced infrared emission coating materials with emissivities close to one unit are critical for producing high-performance standard black bodies. Herein, by utilizing a simple spray-coating method, we prepared a novel carbon-based coating with an organic binder by using VC 811-21 as the main phase and multiwall carbon nanotubes (MWCNTs) as the dopant to fulfil this demand. The addition of an optimal concentration of MWCNTs results in a smooth surface structure with a low roughness that is free of large granularities. The infrared emissivity in the wavelength region of 6.5–16 µm presents a close dependence on the increasing concentration of MWCNTs. With 1‰ MWCNTs, the highest infrared emissivity in vacuum (0.985) is obtained with a spectral nonuniformity of 0.002, and this result is higher than the reported values of VC 811-21 and other well-known infrared coating materials. Such high infrared emissivity will greatly benefit the design of novel black bodies for next-generation infrared remote sensing.

Coarse co-phasing method based on slope of visibility-enhanced dispersed fringe pattern for segmented telescope

Dispersed fringe sensing (DFS) is a promising strategy to bring segmented primary mirror into in-phase for large-aperture segmented telescope. Conventional intensity-based piston extraction methods show operational complexity due to the spectral calibration and poor sensing accuracy for large piston error because of the terrible visibility resulting from the dense fringe modulation. In order to overcome these disadvantages, a visibility improvement technique based on side-lobe enhancement and a slope-based piston extraction algorithm are developed. By scaling up the side lobes in 2-D spectrum of dispersed fringe pattern (DFP), the visibility of DFP could be greatly improved. At the same time, by theoretical analysis, the slope of dispersed fringe is not sensitive to the spectral non-uniformity of the broadband source, thus, the introduced piston extraction algorithm avoids the procedure of spectral calibration. Numerical experiment is conducted to demonstrate its feasibility and accuracy. It provides an efficient, alternative solution to large-scale piston sensing via dispersed fringe sensor.

Physics-based spectral compensation algorithm for x-ray CT with primary modulator

X-ray computed tomography (CT) scatter correction using primary modulator has been continuously developed over the past years, with progress in improving the performance of scatter correction. In this work, we further advance the primary modulator technique towards practical applications where the spectral nonuniformity caused by the modulator continues to be a challenging problem. A physics-based spectral compensation algorithm is proposed to adaptively correct for the spectral nonuniformity, and hence to reduce the resultant ring artifacts on reconstructed CT images. First, an initial spectrum of the CT system without the primary modulator is modeled using an understanding of x-ray CT physics, and optimized by an expectation maximization method; then, the optimized estimation of the initial spectrum is utilized to adaptively calculate the effective modulator thickness from measured transmissions of the primary modulator at each detector element, leading to a set of new spectra that is able to capture the nonuniform spectral distribution of the primary modulator; finally, using the modulator-modeled spectrum, a beam hardening mapping function is generated and beam hardening correction is applied to CT projections. A CatPhan600 phantom and an anthropomorphic thorax phantom were scanned with three different primary modulators to evaluate the approach. For the Catphan phantom, the spectral compensation algorithm efficiently removes the ring (and band) artifacts that otherwise dominate the reconstructed CT image. For the three modulators with nominal copper thickness of 52.5, 105 and 210 m, our method reduces the CT number nonuniformity from 147.9, 436.2 and 696.4 Hounsfield units (HU) to 14.6, 26.2 and 13.6 HU, respectively, close to that of the reference image (i.e. 7.5 HU). For the thorax phantom, the ring artifacts are also suppressed significantly on the transaxial image; on the sagittal image, the alternating black-and-white patterns are largely removed, with the CT number nonuniformity being reduced from 282.0 HU to 38.5 HU.

Surface Plasmon Coupling in Dimers of Gold Nanoparticles: Experiment and Theory for Ideal (Spherical) and Nonideal (Faceted) Building Blocks

The surface plasmon (SP) coupling in dimers of spherical and faceted gold nanoparticles was investigated experimentally and computationally at the single-particle level. Individual ideal dimers of two spherical gold nanoparticles with a constant gap, filled by a self-assembled monolayer of 1,8-octanedithiol linker molecules, exhibit highly uniform dark-field (DF) scattering spectra. In contrast, single nonideal dimers of two faceted gold nanoparticles with the same constant gap exhibit a high degree of spectral nonuniformity. We attribute this significant spectral heterogeneity to the many possible gap morphologies, that is, the many possible configurations of the crystal facet orientations at the junction of the two faceted particles in nonideal dimers. This configurational complexity is reduced in so-called hybrid dimers, which comprise an ideal spherical particle and a nonideal faceted particle. Hybrid dimers were therefore investigated theoretically and experimentally for revealing the influence of cr...

Spectral, spatial, and survivability evaluation of a flash-dried plasma-etched nanotube spray coating.

We demonstrate improved manufacturability of spectrally flat detectors for visible to mid-infrared wavelengths by characterizing a carbon nanotube spray coating compatible with lithium tantalate and other thermal sensors. Compared against previous spray coatings, it demonstrated the highest responsivity yet attained due to both higher absorptivity and thermal diffusivity, while also being matured to a commercially available product. It demonstrated spectral nonuniformity from 300nm to 12μm less than 1% with uncertainty (k=2) under 0.4%. The spatial nonuniformity of the assembled sensor was less than 0.5% over the central half (4mm) of the absorber. As with previous developments employing isotropic carbon nanotube coatings, the absorber surface was sufficiently robust to withstand cleaning by compressed air blast and survived repeated vacuum cycling without measurable impact upon responsivity.

Автоматизация измерения неравномерности магнитной проводимости зубцовой зоны электрических микромашин

A technique for measuring the permeance nonuniformity in rotating transformers based on analyzing the harmonic composition of their permeance is presented. For estimating the permeance nonuniformity, it is proposed to use its influence on the spatial change of the magnetic flux vector position. The suggested technique can be used for diagnosing the operation of not only rotating transformers and selsyns, but also other AC electrical machines. The use of the proposed permeance nonuniforrmity measurement method allows the measurement to be made within a shorter period of time and yields a real permeance variation law. Two schematic designs of experimental benches for implementing the developed technique are proposed, and the bench equipment structure and bench operation principle are described. By using the experimental bench equipment it is possible to obtain extensive data characterizing spectral nonuniformity of the permeance of prototypes and to estimate the accuracy characteristics of rotating transformers and selsyns. A technological bench made according to a simpler design makes it possible to carry out prompt checks of permeance nonuniformity during manufacture of rotating transformers and selsyns, and in periodically performing their calibration checks. The experimentally obtained oscillograms are presented. The external appearance of the obtained graph allows a judgment to be made about the level of rotational pulsations caused by the rotating transformer magnetic circuit anisotropy and the level of pulsations determined by the tooth zone permeance nonuniformity. The use of the proposed technique makes it possible to simplify the permeance nonuniformity measurement process, to visualize it, and to automate technological monitoring of the electrical machinery manufacturing process.

Estimation of Thickness and Cadmium Composition Distributions in HgCdTe Focal Plane Arrays

Mercury cadmium telluride (HgCdTe) is one of the most commonly used material systems for infrared detection. The performance of infrared focal-plane arrays (IRFPAs) based on this material is limited by several noise sources. In this paper, we focus on the fixed pattern noise, which is related to disparities between the spectral responses of pixels. In our previous work, we showed that spectral nonuniformities in a HgCdTe IRFPA were caused by inhomogeneities of thickness and cadmium composition in the HgCdTe layer, using an optical description of the pixel structure. We propose to use this bidimensional dependence combined with experimental spectral responses to estimate disparities of thickness and cadmium composition in a specific HgCdTe-based IRFPA. The estimation methods and the resulting maps are presented, highlighting the accuracy of this nondestructive method.

Prediction of HgCdTe spectral inhomogeneities based on optical and material properties

HgCdTe infrared detectors have been extensively developed over the past few decades. They owe their popularity to the many advantages of HgCdTe material, which has a tunable energy bandgap over the 1–30μm range and high quantum efficiency. They are increasingly used to perform quantitative spectral imaging, which implies a high control of their spectral response. In order to optically model the spectral behavior of this material, it was mandatory to know its refractive index dispersion. The optical properties of this ternary alloy have been particularly studied, as they contribute to detector performance. To the best of our knowledge, however, there are no published measurements of the real part of the refractive index of HgCdTe at low temperatures, above the bandgap energy. We therefore undertook a thorough study of this material at 80K, where we estimated the real part of the refractive index for several alloy compositions in the spectral range of [1800cm-1,6000cm-1]. We used a modified Kramers–Kronig relation, combined with published experimentally measured points. First, we proved the high accuracy of this technique at room temperature, by comparing results with previously published models. We then simulated an HgCdTe bulk layer, in order to extract the dependence of the cut-off wavenumbers on cadmium composition and the layer thickness at low temperature. The influence of these macroscopic parameters on the spectral nonuniformities is discussed.

Toward a Replacement of the CIE Color Rendering Index for White Light Sources

ABSTRACTThe CIE color rendering (fidelity) index (CRI) has remained unchanged for over four decades. Most, if not all, of its components could be updated to more state-of-the-art methods. One of the most critical components of any color rendering (fidelity) metric is the test sample selection. This article therefore addresses the importance of uniform sampling of wavelength space to avoid selective optimization—that is, taking advantage of the unequal contributions of different wavelength regions to the general color rendering score—of light source spectral power distributions. It summarizes the development of a mathematical sample set with undistorted spectral sensitivity, the HL17 set. The set is used in a recently proposed update, the CRI2012 general color rendering index. To assess the impact of the spectrally uniform sample set on color fidelity scores, the CRI2012 index values for each of a set of 139 lamps were compared with those of the CIE CRI. In addition, the impact of updating the other components was investigated. A mean and maximum absolute difference of respectively 5.9 and 21.8 index units were found between the CRI2012 and CIE CRI, although the largest part—respectively 4.03 and 19.7 index units—was shown to be the result of updating the color difference engine and the switch to the CIE 10° observer. The analysis also indicated possible past spectral selective optimization of some warm-white tri-band fluorescent sources for high luminous efficacy of radiation (LER) and (just) sufficient CIE Ra values by taking advantage of the spectral nonuniformity of the CIE reflectance set. Adopting a spectrally uniform sample set in a color rendering metric therefore has important practical implications when designing light source spectra. Finally, possible updates and further improvements of the CRI2012 are briefly mentioned.

Advanced inductively coupled plasma etching processes for fabrication of resonator-quantum well infrared photodetector

Resonator-quantum well infrared photodetectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). To achieve the expected performance, the detector geometry must be produced in precise specification. In particular, the height of the diffractive elements (DE) and the thickness of the active resonator must be uniformly and accurately realized to within 0.05μm accuracy and the substrates of the detectors have to be removed totally. To achieve these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed. Using these etching techniques, we have fabricated a number of R-QWIP test detectors and FPAs with the required dimensions and completely removed the substrates of the test detectors and FPAs. Their QE spectra were tested to be in close agreement with the theoretical predictions. The operability and spectral non-uniformity of the FPA is about 99.57% and 3% respectively.

Short-range surface plasmon propagation supported by stimulated amplification using electrical injection

We have investigated the propagation of the long-range mode (LRSP) and the short-range mode (SRSP) surface plasmon polaritons (SPPs) along the waveguide made from Au film and quantum wells (QWs) gain medium. Influenced by the gain spectral nonuniformity, the SRSP showed narrower spectrum than the LRSP in output, denoting that the SRSP propagation was supported by stimulated amplification (SA) in electrically-pumped QWs. An SRSP output power as large as 1.6 times of that of the LRSP was obtained over a travelling distance of 80 μm. The mechanism of SA-supported SRSP propagation can be adopted for electrical modulation of SPPs.

Use of Derivative Calculations and Minimum Noise Fraction Transform for Detecting and Correcting the Spectral Curvature Effect (Smile) in Hyperion Images

Earth Observing-1 Hyperion data were found to be relatively noisy and to contain significant cross-track spectral curvature nonlinearity disturbances, known as the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">smile/frown</i> effect. A method for the correction of spectral curvature effects (smile) in Hyperion images, termed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">trend line smile correction</i> (TLSC), is presented. The method is based on the assumption that there is a partial correlation between data spectral nonuniformity, due to the smile and eigenvalues gradient that mostly appears in the first minimum noise fraction (MNF) image (MNF-1). However, MNF-1 consists of both spatial and spectral information. Therefore, it is hypothesized that adaptation applied to MNF-1, according to exclusively spectrally derived parameters (e.g., atmospheric absorption features) can account specifically for the smile effect in the data. A set of normalization factors, calculated from the spectral derivative at the right-hand side of the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption feature (760 nm), MNF-1 and the moderate-resolution atmospheric transmittance radiative transfer model, are used to scale the initial MNF-1. The image is corrected after the inverse conversion of the MNF to radiance space. The methodology was tested on four different Hyperion scenes and consistently outperformed other tested methods by up to nine times. As a result, thematic mapping, using the TLSC-corrected reflectance data cube, was shown to be consistent with the geology maps of the study area.

Improved SAC-OCDMA System With Multiple Incoherent Sources

The effect of a nonuniform spectrum on performance of a spectral amplitude coded optical code division multiple access system is investigated. The signal-to-interference ratio (SIR) as a function of nonuniformity of the source spectrum has been computed. Use of multiple sources is proposed to reduce spectral nonuniformity of the source and consequently the SIR.

Development of Calculation Method for Radiative Heat Transfer in an Infrared-active Gas with Narrow-Band Nonuniformity and Its Examination Based on an Absorption Line Data Base (In Case of a Nonisothermal Field Including a Single Infrared-Active Gas)

This paper proposes a rational, explicit and practicable approach for incorporating the spectral non-uniformity of absorption coefficient within a narrow band into a nongray analysis of radiative heat transfer in a nonisothermal field including a single infrared-active species. In the development of this new approach, attention is paid to securing rationality and explicitness even when the approach is applied to nonisothermal fields. This aim is achieved based on the fact that the line center of each absorption line does not move even if the gas temperature varies. Validity of the proposed approach is examined in detail trough comparison of the results obtained by the proposed approach with the results of line-by-line analysis base on a high-resolution database of absorption lines. It was confirmed in a typical nonisothermal field that the proposed approach can properly incorporate the influence of narrow band non-uniformity into a nongray analysis of radiative heat transfer in a nonisothermal field including a single infrared-active species.

In-flight calibration of the ISGRI camera

ISGRI, the IBIS low energy camera (15 keV - 1 MeV) on board INTEGRAL, is the first large CdTe gamma-ray imager in orbit. We present here an overview of the ISGRI in-flight calibrations performed during the first months after launch. We discuss the stability of the camera as well as the CdTe pixels response under cosmic radiation. The energy calibra tions were done using lead and tungsten fluorescence lines and the $\mathrm{^{22}Na}$ calibration unit. Thermal effects and charge correction algorithm are discussed, and the resulting energy resolution is presented. The ISGRI background spatial and spectral non-uniformity is also described, and some image correction results are presented.

Approach for incorporating narrow band nonuniformity into nongray analysis of radiative heat transfer in nonisothermal and nonhomogeneous gas fields

This paper presents a rational, explicit and practicable approach for incorporating the spectral nonuniformity within a narrow band into a nongray analysis of radiative heat transfer. First of all, emphasis is placed on describing the necessity of a new approach for treating this kind of spectral nonuniformity. In the development of this new approach, attention is paid to securing rationality and explicitness even when the approach is applied to nonisothermal fields. This aim is achieved based on the fact that the line center of each absorption line does not move even if the gas temperature varies. Validity of the proposed approach is demonstrated in a typical nonisothermal field. Furthermore, the extension of the proposed approach to the mixture of more than one infrared-active species is discussed and its validity is examined.