Search Results (836)

Multispectral temperature measurement technology based on blackbody radiation theory has been widely applied in the field of non-contact temperature measurement. However, its applicability is limited by the single-point measurement mode. To address this limitation, this study developed a spectral fusion temperature measurement device and proposed a new method for reconstructing the two-dimensional temperature field of deflagration fireballs by fusing spectral and imaging data. The device adopts a CCD sensor and a fiber optic spectrometer placed in parallel with parallel optical axes. To ensure the accuracy of the CCD’s response characteristics at different distances, the photo-response non-uniformity (PRNU) calculation method was used for precision validation. In this study, spectral and imaging data of deflagration fireballs were obtained through experiments. Spectral data of consecutive frames at 189 ms, 192 ms, 195 ms, and 198 ms were extracted and analyzed, confirming that the temperature range at the four time points is 1050 K to 1800 K. The proposed method generates temperature elements with equal temperature intervals and their probabilities within the temperature range, and calculates the theoretical radiation spectrum of each element. Then, least squares optimization fitting is performed on the experimentally measured spectra to obtain the optimal probabilities of the temperature elements in the temperature field. By combining these optimal probabilities with CCD grayscale images, the 2D temperature distribution of the deflagration fireball was reconstructed. Results show that: the PRNU value of the device at a distance of 9 m is less than 2.2% through experimental verification; fused images of the temperature field spectra of four consecutive frames of the deflagration fireball were obtained using the proposed method. The average temperatures reconstructed by the proposed method at 189 ms, 192 ms, 195 ms, and 198 ms were 1382 K, 1373 K, 1366 K, and 1357 K, respectively, while the corresponding temperatures obtained by conventional spectral inversion were 1430 K, 1422 K, 1414 K, and 1406 K. The relative errors were 3.2%, 3.4%, 3.3%, and 3.4%, respectively, with an average relative error of approximately 3.3%. Full article

In this investigation, optical emission spectrometers, a Brinell hardness tester, optical light and scanning microscopes, and X-ray diffraction were used for general metallurgical characterization of the experimental irons in as-cast states. The hole-drilling method was used to assess residual stress distributions under gross and net casting weight conditions. To create experimental irons using the casting process, raw materials were transformed from a solid to a liquid state using an industrial furnace and ladle to melt and cast, respectively. The casting shakeout temperatures for samples A and B were recorded at 60 °C and 180 °C, respectively, after a characteristic stress lattice casting component was allowed to cool for about 1645 min and 1295 min. Chemical analysis verified the experimental hypoeutectic irons of ASTM A532, Type A, Class III, 25%Cr, i.e., high chromium white cast iron alloys. Additionally, it was discovered that micrographs were made of an austenitic-martensitic matrix that contained eutectic M₇C₃ and secondary M₂₃C₆-type carbides. The residual stress distributions were found to be influenced by various carbide and metallic volume fraction proportions, casting section thickness, and casting shakeout duration and temperature. Optimal hardness values, however, were shown to be associated with higher residual stress distributions and an increase in major alloying elements in experimental irons. Consequently, different residual stress distributions are produced by casting shakeout temperatures at lower and higher values under gross and net casting weight conditions. Full article

To circumvent the prohibitive cost of large-format infrared focal plane arrays and the significant spatial–spectral mismatch caused by spectral smile in conventional long-slit configurations, this work develops a low-cost short-wave infrared (SWIR, 1000–2500 nm) hyperspectral imaging system utilizing digital micromirror device (DMD) scanning paired with a single-element detector. A comprehensive analytical model for a prism–reflection grating (P-RG) compound dispersive element is established, enabling the joint optimization of the prism apex angle and grating period to achieve quantitative compensation of spectral distortion across the entire waveband. Based on this model, the optical system is integrated and optimized, while a centroid localization algorithm is implemented to facilitate online calibration of model parameters and real-time reconstruction of the hyperspectral data cube at the DMD plane. Experimental results demonstrate that both smile and keystone distortions are suppressed below $5\mathsf{\mu }\mathrm{m}$ throughout the 1000–2500 nm range, which is superior to the single DMD pixel pitch of $7.6\mathsf{\mu }\mathrm{m}$. The full-field modulation transfer function (MTF) at the Nyquist frequency (32.9 lp/mm) exceeds 0.7, approaching the diffraction limit. Characterization confirms that the system provides 510 spectral channels with an average resolution of 3.57 nm and a spatial resolution of 2.5 $\mathsf{\mu }\mathrm{m}$. By effectively eliminating spectral overlap and cross-column crosstalk on the DMD encoding surface, this system provides a high-fidelity optical front-end for single-pixel imaging, offering a viable technical pathway for the development of affordable SWIR hyperspectral instrumentation. Full article

Localized surface plasmon resonance (LSPR) is an optical phenomenon that occurs when light interacts with free electrons on the surface of metallic thin films, producing intensified electromagnetic fields at specific sites, often called “hot spots”. LSPR-based sensing technologies respond to chemical and associated optical interfacial changes. Inherent advantages include enhanced sensitivity, compact size, low production cost, and strong potential for integration into portable, point-of-care diagnostic systems. This study focuses on a detailed investigation into the surface functionalization of localized surface plasmon resonance (LSPR)-based nanohole array (NHA) sensors for biomedical applications. Gold-coated NHA surfaces were functionalized using polyethylene glycol (PEG) self-assembled monolayers (SAMs), enabling specific attachment of biomolecular species. As a proof-of-concept, bovine serum albumin (BSA) and SARS-CoV-2 nanobody proteins were successfully immobilized on the PEGylated surfaces. Individual steps of surface modification including PEGylation, protein immobilization and nanobody immobilization were validated through a dual-method approach which combined measurement of LSPR optical spectral shifts and x-ray photoelectron spectroscopy (XPS) chemical analyses. Reproducibility was assessed across multiple sensors and repeated trials, confirming the repeatability of each functionalization and binding process. The sensor system, consisting of NHA-based plasmonic platform, microfluidics, and a portable optical spectrometer, exhibits the capability for reliable and sensitive, label-free detection of biomolecular targets, including viral antigens, in liquid-phase environments. Full article

Spaceborne detection of solar-induced chlorophyll fluorescence (SIF) requires extremely high radiometric accuracy, and the polarization characteristics of an ultra-wide swath spaceborne fluorescence ultraspectral camera directly affect the accuracy of SIF retrieval. This study takes an ultra-wide swath camera based on an off-axis three-mirror anastigmat telescope combined with a Littrow–Offner spectrometer as the research object. A full-field-of-view (FOV), full-spectral, pixel-by-pixel polarization testing system was established based on the Stokes–Muller formalism, achieving for the first time fine characterization and calibration of the pixel-level polarization properties of such a payload. The results show that: (1) polarization sensitivity (LPS) exhibits a strong linear positive correlation with wavelength (R² > 0.97), with good uniformity (fluctuation < 1%) across the full ±15° FOV; (2) the polarization sensitive axis (PSA) shows a symmetric distribution across the FOV and gradually approaches 90° as the wavelength increases, with a clear deviation in the short-wavelength bands and stabilization in the mid-to-long wavelength bands; (3) through multiple sets of cross-validation and Monte Carlo statistics, the calibration accuracy reaches 0.1%, and the system uncertainty is better than 0.05%. This study can provide data support and a reference basis for high-accuracy spaceborne SIF retrieval, payload polarization correction, and optical design optimization. Full article

In response to the demands for planetary material detection, in this study, we propose an optical system for a compact remote Raman–LIBS (CRBS, Laser-Induced Breakdown Spectroscopy) combined spectrometer based on liquid lens focusing. This system adopts a design approach incorporating liquid lens focusing, a shared pulsed excitation source, and a common optical path for both transmission and reception. Compared to existing international combined Raman–LIBS spectrometer systems, the proposed optical system is more compact and achieves integrated Raman and LIBS detection capabilities, thereby facilitating system miniaturization and enhancing detection efficiency. This system represents a promising approach for compact, robust remote surface analysis instruments for terrestrial and planetary science. This study provides a theoretical foundation for achieving stable in-orbit detection in lunar material exploration and other long-distance signal detection missions. Full article

Because of high visible and near-infrared (VNIR) reflectance, and deep shortwave infrared (SWIR) absorption, snow and ice are unique among terrestrial land cover. As such, both are well-suited to mapping and monitoring using optical remote sensing. However, to date, almost all studies of snow and ice spectroscopy have been limited to single or small numbers of specific cryospheric environments. These studies serve a diversity of objectives, but together also suggest the importance of the global continuum of snow and ice composition and spectroscopy. The continuum of snow and ice composition gives rise to the characteristics that allow different types of snow and ice to be distinguished optically. Particularly with imaging spectrometers. Characterization of this continuum of reflectance can facilitate development of physical models to quantify snow and ice composition and abundance, particularly in the presence of other types of land cover. In this study, a collection of ~140,000,000 visible through SWIR (VSWIR) reflectance spectra, collected by NASA’s EMIT imaging spectrometer from 56 diverse cryospheric environments, is used to characterize the continuum of snow and ice reflectance. This continuum is characterized using linear dimensionality reduction to quantify the dimensionality and topology of the spectral feature space of snow and ice. The resulting spectral feature space is effectively two-dimensional with a planar spectral feature continuum bounded by dry and wet snow, ice and dark targets (e.g., shadow, water). Because of the near collinearity of snow and ice endmember reflectances, linear spectral mixture models based only on these endmembers are ill-posed and unstable to inversion. However, in landscapes where sufficiently homogeneous seasonal snow is present with other land cover types, the standardized spectroscopic mixture model based on the Substrate, Vegetation and Dark (SVD) continuum can be extended with an instance-specific snow endmember (SVD + snow) to yield plausible areal fraction estimates with small misfits to observed spectra. More generally, the snow–ice-dark continuum can also be represented accurately with an optimal normalized difference index exploiting compositionally distinct differential absorptions at ~650 and ~1230 nm to distinguish dry from wet snow from white and blue ice. This optimized index, referred to as the Continuous Cryosphere Index (CCI), minimizes BRDF effects of topographic slope and aspect relative to illumination, while avoiding the saturation that causes the Normalized Difference Snow Index (NDSI) to conflate wet snow with white and blue ice reflectance. In addition to imaging spectrometers like EMIT, operational sensors like MODIS, VIIRS and WorldView-3 have spectral bands near 650 nm and 1230 nm, so they could also be used for CCI mapping. Full article

High-throughput and compact volume phase holographic (VPH) grating transmission spectrometers are widely employed in scientific research, agriculture, and industrial applications. Conventional transmission spectrometers generally adopt a fixed configuration and therefore have limitations in simultaneously achieving high spectral resolution and broad wavelength coverage. To address the limited tunability of transmission spectrometers, this work presents the theoretical analysis and experimental validation of a transmission spectrometer incorporating a novel catadioptric grating assembly, which consists of a transmitting VPH and a planar reflector. A catadioptric system is a combination of reflective (catoptric) and refractive (dioptric) elements. In the proposed configuration, a VPH grating and a plane mirror arranged at a fixed 90° angle form the catadioptric dispersion module. Synchronous rotation of this assembly enables wavelength scanning. The structure ensures that the diffracted ray along the optical axis of the imaging lens maintains the Bragg condition across the scanning range, thereby preserving maximum diffraction efficiency. The optical configuration and structural parameters of the spectrometer were theoretically derived, and a prototype spectrometer with an f-number of 1.8 employing a 2400 g/mm grating was constructed. Measurements demonstrate that, when the rotation angle is tuned from 30.5° to 50.5°, the accessible spectral range covers from 410 nm to 650 nm. Spectral response measurements using a tungsten–halogen light source confirm that the spectrometer maintains an acceptable diffraction efficiency across the entire tuning range. The measured spectral resolution is 0.1 nm at 626 nm with a 2400 g/mm grating and 0.18 nm with a 1500 g/mm grating. The spectrometer was further applied to fiber-enhanced gas Raman spectroscopy, where it successfully resolved the closely spaced Raman peaks of CH₄ and C₂H₆ that are difficult to distinguish using conventional compact spectrometers. These results demonstrate that the proposed tunable catadioptric spectrometer simultaneously provides excellent wavelength tunability and high spectral resolution. Full article

Precise sculpturing of light empowers light with abundant phenomena across fundamental physics and practical applications. The emergence of metasurfaces provides a pivotal solution to the limitations of traditional optical components, which make it difficult to meet the integration requirements of diverse applications, and they are distinguished by their ultra-thin profiles, low optical losses, and high degree of controllability. In this paper, we elucidate the core physical principles to manipulate phase, amplitude, and polarization with meta-optic architecture, along with nonlocal effects. Specifically, we revisit the research progress and typical applications of meta-waveguides, meta-fibers, meta-lasers, meta-spectrometers, and meta-sensing. Finally, it looks forward to the future development direction of meta-optics in exploring the limits of light field control, chip-scale functional integration, and discovering new physical effects, providing theoretical and technical references for the development of metaphotonic devices. Full article

Spectral interrogation of fiber Bragg gratings (FBGs) in the ~850 nm band remains relatively uncommon, largely due to the limited availability of commercial instruments and the restricted applicability of conventional interrogation schemes in this wavelength range. This work presents a practical and high-precision wavelength demodulation method for 850 nm FBG sensing based on an imaging Charge-Coupled Device (CCD) spectrometer. A Czerny–Turner (C–T) optical configuration is employed for spatial spectral dispersion, and the optical system is theoretically analyzed and optimized using ZEMAX to balance spectral resolution, optical throughput, and compactness. A polynomial wavelength–pixel calibration model is established, and Gaussian fitting is adopted for robust peak-position extraction under multimode fiber conditions. Experimental validation is carried out using four serially cascaded FBGs distributed over 830–880 nm. The wavelength–pixel calibration yields an RMS residual of 0.46 nm. Within a strain range of 0–2000 με, the average wavelength demodulation bias of a single FBG is 6.8 pm, with a wavelength demodulation RMS error of 86.9 pm and a measured strain sensitivity of 0.72 pm/με. The results demonstrate that the proposed CCD-based imaging interrogation scheme is feasible for 850 nm FBG sensing and enables accurate wavelength demodulation in this relatively underexplored band. Since the system is implemented using standard off-the-shelf components, it also provides a practical technical route for the deployment of FBG sensing systems in engineering applications. Full article

A Principal Component-Based Spectral Standardization (PCSS) method was developed to standardize hyperspectral radiance spectra onto a fixed wavelength grid. This enables the direct comparison of radiance or reflectance spectra across different spatial pixels of an imaging spectrometer or between different instruments. The method was validated using simulated Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder (CPF) spectra. The PCSS approach demonstrated high accuracy: the average root-mean-square uncertainty across all CPF channels remained below 0.07%, with maximum individual-channel uncertainties under 1%. Compared to methods based on spectral interpolation, PCSS produced significantly lower biases with tighter error distributions, particularly in spectrally rich regions. Measured Hyper Spectral Imager for Climate Science (HySICS) balloon data provided further validation. PCSS successfully estimated wavelength shifts that closely matched measured data, even when utilizing approximated Jacobians, demonstrating the method’s robustness. Because it relies on a pre-computed lookup table for model parameters, PCSS bypasses the need for intensive radiative transfer calculations, making it highly computationally efficient. Beyond CPF, this method can easily be adapted for other hyperspectral sensors by substituting their respective wavelength grids and instrument line shape functions, offering a powerful tool to improve cross-calibration between different satellite sensors. Full article

Surface ozone monitoring remains challenging due to sparse ground networks and limited satellite boundary-layer sensitivity. This study evaluates, for the first time, China’s Environmental Trace Gases Monitoring Instrument II (EMI-II) for estimating surface ozone over the Beijing–Tianjin–Hebei (BTH) region. EMI-II total ozone columns (TOCs) are retrieved using the differential optical absorption spectroscopy (DOAS) algorithm and validated against the TROPOspheric Monitoring Instrument (TROPOMI) (R = 0.96), Geostationary Environment Monitoring Spectrometer (GEMS) (R = 0.97), and the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) ground measurements (R > 0.92, bias < 4%). TOCs are then combined with ERA5 meteorology, satellite NO₂/HCHO, and surface observations within machine learning models, achieving cross-validated R² of 0.94 and RMSE of 12.05 μg/m³ for surface ozone estimation. EMI-II estimates show strong agreement with independent observations (R = 0.91, RMSE = 10.83 μg/m³) and reproduce seasonal gradients, with summer concentrations (131 μg/m³) more than double winter levels (61 μg/m³). Estimation skill is regime-dependent: performance comparable to TROPOMI occurs under strong photochemical activity, while reduced sensitivity occurs under weak radiation and stable boundary layers—consistent with averaging kernel diagnostics. This first comprehensive validation demonstrates that EMI-II, despite vertical sensitivity limitations, provides meaningful surface ozone constraints under favorable atmospheric conditions. The framework is potentially applicable to other regions and sensors under similar conditions, providing a case study for integrating national satellite products into multi-source surface ozone estimation. Full article

The Middle-Wave Infrared Imaging Spectrometer for Target Asteroids (MIST-A) will be launched in 2028 aboard the Emirates Mission to the Asteroid belt (EMA) and will operate in the 2–5 μm spectral range to study the asteroids’ surface composition and thermo-physical properties. MIST-A’s Optical Head (OH) design is inherited from the Jovian IR Auroral Mapper (JIRAM), from which the instrument also received two spare Hybrid-Thinned Mercury-Cadmium-Telluride (MCT) photodetectors: the Engineering Model EM2 and the Flight Spare FS1. These are tested to assess their performance after a long period of storage. The laboratory setup for testing both detectors consists of a blackbody and a cryostat which houses the focal plane, maintained at temperatures of 85 K, its nominal operative temperature, and 90 K. Two sets of measurements are performed: (1) characterization of the dark current at different integration times (0 ms, 224 ms, 448 ms, 672 ms, 869 ms, 1120 ms); (2) verification of the detectors’ response linearity, measuring a blackbody at different temperatures (from 50 °C to 100 °C), including ambient temperature (25 °C, with the blackbody turned off). The results of these tests confirm that both models are fully operational and allow us to evaluate the consequences of the years of inactivity on their performance. Through a detailed analysis of the detectors’ properties and a comparison study with the results of the sensors’ first characterization performed by their producer in 2009, we come to the conclusion that both instruments are able to fulfill MIST-A’s scientific requirements. The FS1 displays a better performance with respect to the EM2 and for this has been selected as MIST-A’s Flight Model. Full article

To clarify nutritional characteristic differences in mature seeds among flax germplasm resources, 30 accessions (YY01–YY30) were used as materials. Crude protein, 17 hydrolyzed amino acids, 37 fatty acids, crude fat, and mineral elements (Fe, Zn, Ca, Mg) were determined via the Kjeldahl method, amino acid analyzer, gas chromatograph, Soxhlet extraction, and inductively coupled plasma optical emission spectrometer, followed by statistical analysis. Results showed crude protein ranged 12.07–23.97 g/100 g (coefficient of variation, CV = 10.41%), with YY-30, YY-02, and YY-05 as high-protein germplasm (>23 g/100 g); lysine had the highest CV (28.57%) among essential amino acids, EAA, and YY-26’s EAA/total amino acid, TAA, (41.59%) met Food and Agriculture Organization/World Health Organization, FAO/WHO standards. α-Linolenic acid (average 33.6%, max 40.3% in YY-15) was the main functional fatty acid, strongly positively correlated with linoleic acid (R² = 0.9983, p < 0.0001). Crude fat ranged 28.49–40.22% (CV = 7.26%), with YY-26, YY-22, and YY-27 as high-oil germplasm. Fe had the largest CV (16.68%) among the four mineral elements, with YY-30 having the highest Fe content (58.94 mg/kg); in addition, Ca was weakly positively correlated with Mg (p = 0.02). The screened high-quality germplasm and the clarified nutritional differences among flax germplasm resources provide a scientific basis for flax breeding and the development of flax-based functional foods. Full article

Polydimethylsiloxane (PDMS) films doped with graphene nanoplatelets (GNP) with an embossed surface-relief grating were investigated as photothermal actuated sensors. The films were initially characterized using controlled environmental heating where the wavelength of a diffracted white-light probe beam measured at a fixed angle increased monotonically with temperature due to thermal expansion of the grating. An asymmetric double sigmoidal function tracked the shift in peak diffraction wavelength. The observed thermal response is consistent with the thermal expansion of a freestanding PDMS composite film. When a continuous-wave (CW) laser was incident on the film, intensity-dependent photothermal expansion caused a transient deformation in the grating. The photomechanical behavior of the grating, tracked by the diffracted probe beam with a miniature spectrometer, was then shown to act as a laser power meter. These results demonstrate that photomechanical materials can be used as add-ons to existing optical spectroscopy devices for power-sensing applications. Full article