Spectral Dispersion Research Articles

The Optical System Design of a Space-Based Wide-Field Infrared Slitless Spectrometer

With the increasingly complex space environment, the operational safety of spacecraft faces severe challenges, creating an urgent need to develop efficient and reliable space target detection and identification technologies. Traditional optical detection equipment faces significant challenges in space target detection and identification due to the low signal-to-noise ratio of space targets. To address the limited field of view (FOV) of traditional spectrometers, this paper proposes an improved wide-FOV infrared slitless spectrometer system based on the Dyson spectrometer. The system consists of three main components: a front telescope system, a spectral dispersion system, and a relay lens system. The front telescope system adopts a Ritchey–Chrétien structure and incorporates a correction lens group to enhance imaging quality. To overcome the practical challenges of conventional Dyson spectrometers—such as the high difficulty and cost in manufacturing and aligning concave gratings—an improved Dyson spectrometer based on a planar blazed grating is designed. A collimating lens group is incorporated to reduce spectral line curvature and chromatic aberration while ensuring a linear spectral dispersion relationship, achieving “spectrum-value unification” in the system. Additionally, a secondary imaging relay lens system is designed to ensure 100% cold stop matching efficiency, thereby minimizing stray light interference. Through optimization and ray tracing using optical design software, the final system achieves a field of view of 0.69° × 0.55°, a spectral resolution of 8.41 nm/pixel, spectral line curvature and chromatic aberration both below 10 µm, and a nearly linear spectral dispersion relationship, realizing spectrum-value unification to facilitate target identification. This infrared slitless spectrometer can stably acquire the spectral characteristics of space targets without requiring high-precision theodolites, providing a novel technical solution for the identification of dynamic space targets. It holds broad application prospects in space surveillance and related fields.

Improvement of Ice Particle Spectral Relative Dispersion Parameterization in the BCC‐AGCM Model and Its Impact on Global Climate Simulation

AbstractThe representation of cloud microphysical processes in climate models continues to be a major challenge leading to uncertainty in climate simulations. The shape parameter (equivalent to relative dispersion) of gamma distribution for ice particles is assumed to be 0 in the Beijing Climate Center Atmospheric General Circulation Model (BCC‐AGCM). This study diagnoses the shape parameter by linking it to the ice volume‐mean diameter and analyzes the impact of the modified scheme on the performance of climate simulations. Results show that the modified scheme performs better in simulating global cloud fraction, cloud radiative forcing, and total precipitation compared to the control configuration, thereby significantly reducing simulation biases. The underlying physical mechanisms are driven by three key factors. First, the shape parameter in the modified scheme is greater than zero, narrowing the ice particle size distribution. This reduces the autoconversion of ice to snow and sedimentation processes while enhancing deposition growth, resulting in an increase in upper‐level ice clouds. The increase in ice‐clouds increases upper atmospheric temperatures, enhances atmospheric stability, and promotes the formation of lower‐level clouds. Second, the improvement in cloud fraction significantly mitigates the underestimation of longwave and shortwave cloud radiative forcing. Additionally, the overestimation of precipitation is improved, including both convective and large‐scale precipitation, particularly from an annual mean perspective. Increased atmospheric stability reduces convective precipitation, while weakened snow sources and enhanced sinks to reduce large‐scale precipitation. The study emphasizes the importance of ice particle spectral relative dispersion and provides valuable insights for improving cloud microphysics parameterization schemes.

Experimental and on-sky demonstration of spectrally dispersed wavefront sensing using a photonic lantern.

Adaptive optics (AO) systems are critical in any application where highly resolved imaging or beam control must be performed through a dynamic medium. Such applications include astronomy and free-space optical communications, where light propagates through the atmosphere, as well as medical microscopy and vision science, where light propagates through biological tissues. Recent works have demonstrated common-path wavefront sensors (WFSs) for adaptive optics using the photonic lantern (PL), a slowly varying waveguide that can efficiently couple multi-moded light into single-mode fibers (SMFs). We use the SCExAO astrophotonics platform at the 8 m Subaru Telescope to show that spectral dispersion of lantern outputs can improve correction fidelity, culminating with an on-sky demonstration of real-time wavefront control. This is the first, to the best of our knowledge, result for either a spectrally dispersed or a photonic lantern wavefront sensor. Combined with the benefits offered by lanterns in precision spectroscopy, our results suggest the future possibility of a unified wavefront sensing spectrograph using compact photonic devices.

Functional 31P Magnetic Resonance Spectroscopy at 9.4 T.

Functional 31P MRS might give valuable information on the energy metabolism of the brain during stimulation. However, the tiny expected spectral changes are difficult to detect due to low SNR and large voxel sizes. Higher field strengths and sensitive multielement arrays could help to investigate the energy metabolism during brain activation. Here, we acquired functional 31P MRS data during visual stimulation at 9.4 T using a 27-element receive array and an optimized 3D-CSI protocol. First, T1 values at that field strength were measured, confirming a decrease in T1 times for increasing fields. Then, a 4.5 min visual stimulus with varying color scheme and frequency was presented to healthy subjects during CSI acquisition for 45 min. Stimulus and rest signals were formed by averaging over five epochs, resulting in spectra with high spectral quality and SNR. Stimulus and rest spectra were almost identical, except for a very small but significant difference in the chemical shift of inorganic phosphate, which might indicate a slight increase in pH during stimulation. It was then investigated whether postprocessing algorithms might be able to detect more subtle changes. Spectral denoising using a principal component approach resulted in improved SNR with high spectral integrity but suppressed the chemical shift difference. Spatial deconvolution improved the spatial resolution but did not yield changes in the outcome. Those results indicate that only very subtle changes in the 31P spectrum due to visual stimulation can be expected, which are difficult to detect even when taking advantage of the high SNR and spectral dispersion at 9.4 T.

Propagating and non-propagating waves in generally anisotropic multi-layered composites: comparative study of the semi-analytical finite element method, spectral collocation method and dispersion calculator

This paper presents a comparative study of the various methods employed for obtaining dispersion curves and displacement profiles in multi-layered composites of diverse engineering applications. The linearization of the eigenvalue problems resulting from the Semi-Analytic Finite Element method (SAFE) and the Spectral Collocation Method (SCM) enables the study of propagative and non-propagative phenomena in ultrasonic guided waves. Initial validation of the established algorithms was performed using elastic and viscoelastic media in homogenized and hybrid multi-layered composites. A relative error of less than 0.02% was achieved when comparing the algorithms to the DISPERSION CALCULATOR (DC) software. Additionally, the SAFE method exhibited a substantial advantage in processing speed when compared to SCM, particularly when dealing with a considerable number of layers, up to 48 layers. Furthermore, a modes separation technique is applied, demonstrating the phenomenon of conversion of non-propagative modes into propagative modes. In terms of displacement profiles, the SAFE method has been demonstrated to exhibit enhanced precision. The objective of this manuscript is to provide a concise overview of the benefits and barriers of each approach to assist in selecting the appropriate program and optimal parameters for effective application in the NDT.

Enhanced Conditional Ground Motion Selection Model Considering Spectral Compatibility and Variability of Three Components for Multi-Directional Analysis

In this study, the solution model based on the stochastic harmony search algorithm was proposed to obtain real ground motion (GM) records for nonlinear dynamic analysis of structures. Obtaining the GM record problem was formulated as a constrained engineering optimization problem. The solution model ensures spectral compatibility between the mean horizontal spectrum of selected ground motion (GM) records and the target horizontal spectrum, as well as the mean vertical spectrum of the selected GMs with the target vertical spectrum. This model also allows the management of record-to-record variability in both horizontal and vertical components of the selected GMs. Moreover, the model effectively addresses the period-dependent record-to-record variability in all orientations of seismic excitations simultaneously using a single-scale value, preserving the relative amplitude and phasing of actual GM components. The efficiency of the model has been demonstrated through numerical examples with various uniform hazard spectra, specifically those based on Eurocode-8 and the Turkish Building Earthquake Code, as well as scenario-based target spectra. The results demonstrate that through using the proposed model it is possible to obtain GM records with the desired spectral compatibility and spectral dispersion for both horizontal and vertical GM components. Thus, the model can be used as an efficient way to obtain appropriate GM records for nonlinear dynamic analyses of both two- and three-dimensional structural models for performance-based designs and/or evaluation frameworks, considering seismic excitations in both horizontal and vertical directions.

Improved Parameterization of Cloud Droplet Spectral Dispersion Expected to Reduce Uncertainty in Evaluating Aerosol Indirect Effects

AbstractRelative dispersion (ε), as a parameter characterizing droplet spectral shape, exerts a considerable impact on cloud radiation and precipitation processes, and its accurate parameterization is urgently needed in models. Current ε parameterizations, which are based on droplet number concentration or simply set as constants, are inadequate to satisfy the demand. This study shows, utilizing in‐situ cloud and fog observations from five underlying surface regions (urban, suburban, mountainous, coastal and rainforest) of China, that ε uniformly and stably manifests as initially increasing then decreasing as volume‐mean diameter increases across these regions. Based on this relationship, a ε parameterization is established, which exhibits improved predictive capabilities in evaluating both cloud albedo effect and cloud lifetime effect. The parameterization is expected to enhance cloud simulation accuracy and minimize discrepancy between observed and simulated cloud radiation and precipitation, particularly for weather and climate models that commonly use the double‐moment cloud microphysical schemes.

Investigation on coaxial pseudo-fault characteristics induced by the outer ring defect in the single-sided axle-box bearing of wheelset in urban rail vehicles

An in-depth understanding of vibration characteristics of the coaxial pseudo-fault in axle-box bearings installed coaxially on both sides of the wheelset is essential for distinguishing the real fault and the pseudo-fault in axle-box bearing condition monitoring. Therefore, a bearing-vehicle-track coupled dynamic model is developed, which incorporates an axle-box bearing dynamic model with an outer ring defect and a vehicle-track coupled dynamic model. The axle-box vibration responses on both sides of the wheelset, considering single-sided bearing defects with different widths at different vehicle speeds, are obtained through simulation and subsequently analyzed. The results indicate that the coaxial pseudo-fault effect is more pronounced under a defect width of 3 mm. The amplitude, root mean square (RMS), and shock pulse method (SPM) indicators of the axle-box vibration response on the defective side exceed those on the healthy side. The impulse response transmitted to the healthy side consistently lags behind that generated on the defective side. The minimum lag time is 0.0011 s. The fault frequency components and harmonics on the healthy side are more dispersed and decay more rapidly. Finally, based on amplitude-related features and spectral energy dispersion characteristics, a criterion for identifying the coaxial pseudo-fault is proposed using the frequency variance (VF) indicator, and the rationality of the proposed indicator range is demonstrated through field test data.

Simultaneous Incorporation of Magnetic and Plasmonic Nanocrystals in a Chiral Conducting Polymer Yields Unprecedented Magneto-Optic Response.

The creation of next-generation flexible and conformable magneto-optic (MO) materials with dramatically enhanced Verdet constant will significantly advance technologies, including optical isolation, magnetic quantum spin fluctuation measurements, and cold atom spin coherence probes, while opening new possibilities for mapping weakly emanating magnetic fields from sources, including microelectronics or brain activity. The results presented here show that the natural coupling of electric and magnetic dipoles in a chiral polymer with large optical activity (circular birefringence) is significantly enhanced by combined plasmonic field and magnetic interactions of plasmonic nanostarsand magnetic nanoparticlesto yield a dramatically increased Verdet constant within an optical path of a few hundred nanometers. A 175 ± 10 nm film of this material produces up to 600 mdeg of relative MO rotation at 510 nm, which translates to a record-high Verdet constant of 3.1 × 107 deg T-1 m-1 at 93 K, more than two orders of magnitude higher than the current state of the art MO garnet crystals. The room temperature Verdet constant substantially exceeds that of other thin film nanocomposites reported to date. Manipulation of electric and magnetic coupling offers an unprecedented opportunity to tailor the magnitude, sign, and spectral dispersion of the Verdet constant over a broad range of wavelengths.

Band Tones: Auditory Stream Segregation with Alternating Frequency Bands

Abstract An alternating tone sequence may be perceptually integrated into one stream or segregated into two streams based on pitch and timbre differences between the tones (sequential stream segregation). However, the effect of the spectral dispersion of harmonic complex tones on sequential stream segregation has been largely unexplored. We introduced band tones that were harmonic complex tones divided into several frequency bands, in which frequency components in every other frequency band were removed. Here, we show that segregation was reported more often with fewer frequency bands and larger separation in fundamental frequency. Listeners generally responded to 2–8-band stimuli as segregated most of the time. However, the percentages of segregation responses for 16-band stimuli were generally dominated by fundamental frequency separations and whether the movements of fundamental frequencies and band-like spectral patterns were congruent or incongruent. The results suggest that the auditory system cannot organize rapidly alternating frequency component blocks spanning a wide frequency range into one stream.

Demonstration of controlled spatial incoherence for beam smoothing

A concept for beam smoothing of high-energy laser systems is demonstrated. Multiple coherent beams are multiplexed so that their incoherent mix decreases the far-field nonuniformity after random spatial phase modulation introduced by a phase plate. Modeling shows that the incoherent mix effectively leads to the expected scaling in terms of the number of uncorrelated beams, and that spatial multiplexing can be combined with smoothing by spectral dispersion. The results of an experimental demonstration of this concept with up to six beams, leading to more than 40 modes with polarization multiplexing and angular dispersion, are consistent with expectations. The potential practical advantages of this smoothing scheme and future developments are discussed.

A Systematic Study of Inverting Overlappograms: MaGIXS—A Case Study

Abstract Slitless (or wide-field) imaging spectroscopy provides simultaneous imaging and spectral information from a wide field of view, allowing for rapid spectroscopic data collection from extended sources. Depending on the size of the extended source, combined with the spatial resolution and spectral dispersion of the instrument, there may be locations in the focal plane where spectral lines from different spatial locations overlap on the detector. An unfolding method is successfully developed and demonstrated on the recent rocket flight of the Marshall Grazing Incidence X-ray Spectrometer, which observed several strong emission lines in the 8–30 Å wavelength range from two X-ray bright points and a portion of an active region. In this paper, we present a systematic investigation of the parameters that control and optimize the inversion method for unfolding slitless spectrograph data.

NMR Spectral Editing, Water Suppression, and Dipolar Decoupling in Low-Field NMR Spectroscopy Using Optimal Control Pulses and Multiple-Pulse Sequence.

Spectral dispersion in low-field nuclear magnetic resonance (NMR) can significantly affect NMR spectral analysis, particularly when studying complex mixtures like metabolic profiling of biological samples. To address signal superposition in these spectra, we employed spectral editing with selective excitation pulses, proving it to be a suitable approach. Optimal control pulses were implemented in low-field NMR and demonstrated their capability to selectively excite and eliminate specific amino acids, such as phenylalanine and taurine, either individually or simultaneously. The broadening of NMR signals in viscous samples, like bio samples, due to homonuclear dipolar coupling often leads to loss of spectral details, impacting spectral assignments. Therefore, in this work, the multiple-pulse WAHUHA sequence at both high and low field NMR was employed resulting in approximately 63 and 25% reduction in line widths respectively, evident from line width changes in the NMR spectra. The effectiveness of this process was validated by comparing its performance with that of magic angle spinning NMR. Additionally, water suppression was achieved through selective excitation by adding a term representing the water signal to the overall Hamiltonian, expressing the water signal peak frequency, and covering adjacent frequencies on both sides of the water peak within the water signal.

Advancements in surface-enhanced femtosecond stimulated Raman spectroscopy: exploring factors influencing detectability and shapes of spectra.

A combination of femtosecond stimulated Raman scattering and surface-enhanced Raman scattering, termed surface-enhanced stimulated Raman scattering (SE-FSRS), was proposed to leverage both temporal precision and sensitivity for advanced molecular dynamics analysis. During the initial successful implementations of this approach, unexpected spectral distortions were observed, and several potential explanations were proposed. Further progress in this novel technique and its broader implementation requires a profound understanding of the factors influencing the shape of the registered spectra and the underlying mechanisms. Here we present findings on how pulse energy and excitation wavelengths affect SE-FSRS spectra, emphasizing the influence of a strong broadband background on spectral dispersion. These insights contribute to understanding the complex mechanisms underlying SE-FSRS and suggest methods to improve the control and application of this spectroscopic technique, highlighting its potential to provide deeper insights into molecular dynamics. This work represents a significant step toward exploiting SE-FSRS for advanced analytical applications.

Time-resolved cross-beam energy transfer in strongly damped regime on the Laser Mégajoule facility

We report on an experiment performed at the Laser Mégajoule facility to investigate on cross-beam energy transfer (CBET) between two kilojoule-nanosecond laser beams propagating through a neo-pentane gas pipe. CBET is diagnosed using time-resolved transmission measurements and x-ray imagers. The time-resolved laser transmission is obtained using laser calibrated x-ray emission conversion on a gold foil located behind the target. Different shots, with and without frequency shift, allow to control the amount of power transferred between the two beams. In particular, we observe that the blue-shifted pulse is significantly depleted during several nanoseconds when using a frequency shift between the laser beams. The time-resolved data provide quantitative comparisons for benchmarking CBET modeling in our radiative hydrodynamic code. It appears that the x-ray emission from the gold foil is recovered only when no saturation of the ion acoustic wave amplitude is applied in our linear kinetic modeling. Yet, the measured signal is not sufficiently accurate to discriminate between CBET models assuming a perfect plane wave closure and those taking into account the speckle structure of the field with smoothing by spectral dispersion.

A One-Dimensional Model for Investigating Scale-Separated Approaches to the Interaction of Oceanic Internal Waves

Abstract High-frequency wave propagation in near-inertial wave shear has, for four decades, been considered fundamental in setting the spectral character of the oceanic internal wave continuum and for transporting energy to wave breaking. We compare idealized ray-tracing numerical results with metrics derived using a wave turbulence derivation for the kinetic equation and a path integral to study this specific process. Statistical metrics include the time-dependent ensemble mean vertical wavenumber, referred to as a mean drift; dispersion about the mean drift; time-lagged correlation estimates of wavenumber; and phase locking of the wave packets with the background. The path integral permits us to identify the mean drift as a resonant process and dispersion about that mean drift as nonresonant. At small inertial wave amplitudes, ray tracing, wave turbulence, and the path integral provide consistent descriptions for the mean drift of wave packets in the spectral domain and dispersion about the mean drift. Extrapolating these results to the background internal wavefield overpredicts downscale energy transports by an order of magnitude. At oceanic amplitudes, however, the numerics support diminished transport and dispersion that coincide with the mean drift time scale becoming similar to the lagged correlation time scale. We parse this as the transition to a non-Markovian process. Despite this decrease, numerical estimates of downscale energy transfer are still too large. We argue that residual differences result from an unwarranted discard of Bragg scattering resonances. Our results support replacing the long-standing interpretive paradigm of extreme scale-separated interactions with a more nuanced slate of “local” interactions in the kinetic equation.

Deciphering the emission dynamics of colloidal PbS quantum dots: a spectroscopic exploration under diverse environmental and experimental conditions.

This study employs a combination of spectroscopic techniques, including absorption, photoluminescence (PL), time-resolved PL kinetics, and transient absorption measurements, to elucidate the dynamics of excited states of oleic acid (OA)-capped colloidal PbS quantum dots (QDs) in toluene with a mean size of approximately 3 nm. PL decay profiles were properly treated employing either fitting or fitting-free models to extract average decay lifetimes and lifetime distributions. Our findings highlight the profound impact of factors such as particle concentration, size, surface treatment, and the surrounding environment on the optical properties of PbS QDs. We observed a notable blue shift in both absorption and emission spectra, along with shorter decay lifetimes, when the concentration of the particles was reduced. This effect was attributed to the dynamics of concentration-selective ligand desorption on the surface of PbS QDs. An observed distinct peak in the spectral dispersion of average lifetimes was linked to an external origin, which was proved by the addition of varying OA volumes, evidently affecting these features. This study also explores how the PL emission of PbS QD suspensions varies with experimental parameters, such as excitation pulse duration and laser power. A gradual reduction in average lifetimes was demonstrated under the modulation of pulse duration from 15 μs to 150 ns, illustrating a transition from continuous-wave (cw) excitation to quasi-pulsed excitation. This transition was shown to be accompanied by a noticeable shift in the lifetime distributions towards shorter durations, as a consequence of various onset components in the QD ensemble. Comparing with truly pulsed excitation, we experimentally confirmed that the amplitude-average lifetime under cw excitation matches the intensity-average lifetime under pulsed excitation. Lastly, we noted linear and nonlinear behaviors in the PL amplitude as a function of excitation power, with the average lifetime remaining nearly constant under pulsed excitation conditions.

Study of CdSe thin films using the spectroscopic ellipsometry method

In this research, we investigated the optical properties of CdSe thin films on glass substrates using spectroscopic ellipsometry. The samples were analysed using an M-2000 rotation compensator spectroscopic ellipsometer at room temperature, covering a photon energy range of 1.5-7.0 eV. We used an appropriate dispersion model to obtain the spectral dispersion of the optical constants. We calculated the thickness, dielectric permittivity (real and imaginary parts), refraction, and extinction coefficients of the thin layers. The results showed high transparency that varied with the size of the CdSe thin films. Additionally, we determined the bandgap width for samples with thicknesses of 350 nm and 400 nm, which were produced using the chemical deposition method.

Hyperpolarized 13C NMR Metabolomics of Urine Samples at Natural Abundance Applied to Chronic Kidney Disease.

NMR is a central tool in the field of metabolomics, thanks to its ability to provide valuable structural and quantitative information with high precision. Most NMR-based metabolomics studies rely on 1D 1H detection, which is heavily limited by strong peak overlap. 13C NMR benefits from a wider spectral dispersion and narrower signal line width but is barely used in metabolomics due to its low sensitivity. Dissolution dynamic nuclear polarization (d-DNP) offers an opportunity to improve 13C NMR sensitivity by several orders of magnitude. Here, we show that this emerging hyperpolarized metabolomics approach can provide meaningful information about clinical samples. Achieving sub-mM limits of detection with 13C at natural abundance in urine samples was made possible by a meticulous design of the experimental workflow. The analysis of human urine samples from patients with different stages of chronic kidney disease (CKD) was performed using 13C d-DNP NMR and benchmarked to conventional 1H NMR metabolomics at a high magnetic field to explore the complementarity between the two methods. Multivariate analysis of the d-DNP 13C NMR dataset provided a statistical model able to distinguish patients with CKD from control patients. Moreover, 13C d-DNP NMR spectra highlighted several biomarkers known to be biologically relevant. Some of them were in agreement with those obtained with conventional 1H NMR, and the results also highlighted the complementarity of biomarker coverage between hyperpolarized and conventional NMR metabolomics. In particular, 13C hyperpolarized NMR allowed the annotation of two biomarkers that could not be detected by 1H NMR because of peak overlap (i.e., guanine and guanidoacetate).

Nonlinear spectral dispersion in resonant Auger scattering from SF6 for studying nuclear potentials and dynamics

In this study, we integrate experimental observations and theoretical models to elucidate the complex phenomena observed in the resonant S K-edge Auger scattering spectra of the SF6 molecule. A two-dimensional spectral map, constructed of incident photon energy and kinetic energy of the emitted Auger electron, is shown to be a versatile tool for understanding a character of the core-excited potential energy surface and change of the molecular geometry. Our findings reveal how the distinct dispersion behavior of multiple spectral lines enables mapping of ultrafast dynamics within the short-lived core-excited states. Our results confirm the presence of nuclear dynamics in the S1s−16a1g1 and S1s−16t1u1 core-excited states, while dynamics is absent in the S1s−17t1u1 state. Using a combination of analysis, simulations with Coulomb model potentials, and a simple analytical approximation, we qualitatively demonstrate how the varying characteristics of spectral dispersion—classified as Raman, non-Raman, and anti-Raman—mirror the relative gradients of the intermediate and final states in the resonant x-ray scattering process. This insight allows for the effective mapping of molecular potential energy curves, offering a prospective tool on the underlying mechanisms of resonant Auger scattering and its potential for probing molecular dynamics. Published by the American Physical Society 2024