Search Results (1,113)

Metasurfaces have emerged as a unique group of two-dimensional ultra-compact subwavelength devices for perfect wave absorption due to their exceptional capabilities of light modulation. Nonetheless, achieving high absorption, particularly with multi-band broadband scalability for specialized scenarios, remains a challenge. As an example, the presence of atmospheric windows, as dictated by special gas molecules in different infrared regions, highly demands such scalable modulation abilities for multi-band absorption and filtration. Herein, by leveraging the hybrid effect of Fabry–Perot resonance, magnetic dipole resonance and electric dipole resonance, we achieved multi-broadband absorptivity in three prominent infrared atmospheric windows concurrently, with an average absorptivity of 87.6% in the short-wave infrared region (1.4–1.7 μm), 92.7% in the mid-wave infrared region (3.2–5 μm) and 92.4% in the long-wave infrared region (8–13 μm), respectively. The well-confirmed absorption spectra along with its adaptation to varied incident angles and polarization angles of radiations reveal great potential for fields like infrared imaging, photodetection and communication. Full article

In order to achieve a high-precision synchronous detection of two different refractive index (RI) analytes, a D-type surface plasmon resonance (SPR) photonic crystal fiber (PCF) RI sensor based on two channels is designed in this paper. The sensor uses a D-shaped planar region of the PCF and a large circular air hole below the core as the sensing channels. Surface plasmon resonance is induced by applying a coating of gold film on the surface. The full-vector finite-element method (FEM) is used to optimize the structural parameters of the optical fiber, and the sensing characteristics are studied, including wavelength sensitivity, RI resolution, full width at half maximum (FWHM), figure of merit (FOM), and signal-to-noise ratio (SNR). The results show that the channel 1 (Ch 1) can achieve RI detection of 1.36–1.39 in the wavelength range of 1500–2600 nm, and the channel 2 (Ch 2) can achieve RI detection of 1.46–1.57 in the wavelength range of 2100–3000 nm. The two sensing channels can detect independently or simultaneously measure two analytes with different RIs. The maximum wavelength sensitivity of the sensor can reach 30,000 nm/RIU in Channel 1 and 9900 nm/RIU in Channel 2. The RI resolutions of the two channels are 3.54 × 10⁻⁶ RIU and 10.88 × 10⁻⁶ RIU, respectively. Therefore, the sensor realizes dual-channel high- and low-RI synchronous detection in the ultra-long wavelength band from near-infrared to mid-infrared and achieves an ultra-wide RI detection range and ultra-high wavelength sensitivity. The sensor has a wide application prospect in the fields of chemical detection, biomedical sensing, and water environment monitoring. Full article

In the textile industry, cotton and polyester (PES) are among the most used fibres to produce clothes. The correct identification and accurate composition estimate of fibres are mandatory, and environmentally friendly and precise techniques are welcome. In this context, the use of near-infrared (NIR) and mid-infrared (MIR) spectroscopies to distinguish between cotton and PES samples and further estimate the cotton content of blended samples were evaluated. Infrared spectra were acquired and modelled through diverse chemometric models: principal component analysis; partial least squares discriminant analysis; and partial least squares (PLS) regression. Both techniques (NIR and MIR) presented good potential for cotton and PES sample discrimination, although the results obtained with NIR spectroscopy were slightly better. Regarding cotton content estimates, the calibration errors of the PLS models were 3.3% and 6.5% for NIR and MIR spectroscopy, respectively. The PLS models were validated with two different sets of samples: prediction set 1, containing blended cotton + PES samples (like those used in the calibration step), and prediction set 2, containing cotton + PES + distinct fibre samples. Prediction set 2 was included to address one of the biggest known drawbacks of such chemometric models, which is the prediction of sample types that are not used in the calibration. Despite the poorer results obtained for prediction set 2, all the errors were lower than 8%, proving the suitability of the techniques for cotton content estimation. It should be stressed that the textile samples used in this work came from different geographic origins (cotton) and were of distinct presentations (raw, yarn, knitted/woven fabric), which strengthens our findings. Full article

Chalcogenide glasses have broad applications in the mid-infrared optoelectronics field and as phase-change materials (PCMs) due to their unique properties. Chalcogenide glasses can have crystalline and amorphous phases, making them suitable as PCMs for reversible optical or electrical recording. This study provides an in-depth analysis of the evaporation kinetics of indium-doped chalcogenides, GeTe₄ and GeTe₅, using the physical vapor deposition technique on glass substrates. Our approach involved a detailed examination of the evaporation process under controlled temperature conditions, allowing precise measurement of rate changes and energy dynamics. This study revealed a significant and exponential increase in the evaporation rate of GeTe₄ and GeTe₅ with the introduction of indium, which was particularly noticeable at higher temperatures. This increase in evaporation rate with indium doping suggests a more complex interplay of materials at the molecular level than previously understood. Furthermore, our findings indicate that the addition of indium affects the evaporation rate and elevates the energy requirements for the evaporation process, providing new insights into the thermal dynamics of these materials. This study’s outcomes contribute significantly to understanding deposition processes, paving the way for optimized manufacturing techniques that could lead to more efficient and higher-performing optoelectronic devices and memory storage solutions. Full article

The development of new methods of identification of active pharmaceutical ingredients (API) is a subject of paramount importance for research centers, the pharmaceutical industry, and law enforcement agencies. Here, a system for identifying and classifying pharmaceutical tablets containing acetaminophen (AAP) by brand has been developed. In total, 15 tablets of 11 brands for a total of 165 samples were analyzed. Mid-infrared vibrational spectroscopy with multivariate analysis was employed. Quantum cascade lasers (QCLs) were used as mid-infrared sources. IR spectra in the spectral range 980–1600 cm⁻¹ were recorded. Five different classification methods were used. First, a spectral search through correlation indices. Second, machine learning algorithms such as principal component analysis (PCA), support vector classification (SVC), decision tree classifier (DTC), and artificial neural network (ANN) were employed to classify tablets by brands. SNV and first derivative were used as preprocessing to improve the spectral information. Precision, recall, specificity, F1-score, and accuracy were used as criteria to evaluate the best SVC, DEE, and ANN classification models obtained. The IR spectra of the tablets show characteristic vibrational signals of AAP and other APIs present. Spectral classification by spectral search and PCA showed limitations in differentiating between brands, particularly for tablets containing AAP as the only API. Machine learning models, specifically SVC, achieved high accuracy in classifying AAP tablets according to their brand, even for brands containing only AAP. Full article

We report a 2.8 μm all-fiber high-power and high-energy gain-switched Er³⁺:ZBLAN laser based on dielectric fiber mirror and fiber-tip protection. The fiber pigtail mirror, specifically designed for dichroic operation (i.e., anti-reflection at 976 nm pump wavelength and high-reflection around 2.8 μm laser wavelength), shows high damage density of >10 MW/cm². An anti-reflection protective film is coated on the input tip of Er³⁺:ZBLAN fiber and an AlF₃ endcap is spliced to the output tip of Er³⁺:ZBLAN fiber for mitigating the fiber-tip photodegradation and high-power catastrophic failure at 2.8 μm. The compact all-fiber cavity is formed by efficiently connecting the Er³⁺:ZBLAN fiber with dielectric fiber mirror using the standard FC/PC fiber adaptor. When the 976 nm pump operates in pulsed regime, the all-fiber mid-infrared gain-switched laser can be attained with two states of single-pulse and pulse-burst output. The extracted maximum pulse energy is 4.8 μJ in the single-pulse state, and the shortest pulse width is 426 ns. The pulse-burst mode can generate a maximum average power of 5.291 W and burst energy of 264.55 μJ. This work may offer a promising way to realize the low-cost, all-fiber, high-power and high-energy gain-switched laser at MIR wavelengths. Full article

The thermal and optical properties of 60TeO₂-20K₂TeO₃-10WO₃-10Nb₂O₅ (in mol%) glasses doped with Ho₂O₃, Er₂O₃, and Tm₂O₃ were explored in the present work. The thermal stability, refractive index n, extinction coefficient k, absorption coefficient α, and optical band gap of the glasses were evaluated. The UV–Vis–NIR absorption spectra, the Judd–Ofelt intensity parameter, the spectroscopic quality factor, and the emission and absorption cross-sections were calculated to investigate the effects of Er³⁺ and Tm³⁺, respectively, on the band spectroscopic properties of Ho³⁺ ions. The results showed that the maximum emission cross-section was approximately $8\times {10}^{-21} {\mathrm{c}\mathrm{m}}^2$, and the values of the full width at half maximum ($FWHM)$, quality factor (${\sigma }_e\times FWHM)$, and gain coefficient of Ho³⁺: ⁵I₇$\to$⁵I₈ were also reported. The value of the $FWHM\times {\sigma }_e$ was $1200\times {10}^{-28} {\mathrm{c}\mathrm{m}}^3$, which showed greater gain characteristics than earlier study results. For $2 \mathsf{\mu }\mathrm{m}$ mid-infrared solid-state lasers, the glasses that were examined might be a good host material. Full article

Given its huge economic, nutritional, and social value, extra virgin olive oil (EVOO) is an essential food. This flagship product of the countries bordering the Mediterranean basin is one of the most frauded products worldwide. Although traditional chemical analyses have demonstrated to be reliable tools for olive drupes and EVOO quality assessment, they present several drawbacks; the urgent need for fast and non-destructive techniques thus motivated this review. Given the lack of comprehensive reviews in the literature, our first aim was to summarize the current knowledge regarding applying spectroscopies, imaging analyses, and other non-destructive techniques to olives and EVOO. The second aim was to highlight the most innovative and futuristic applications and outline the future research prospects within this strategic production chain. With respect to olive drupes, the most interesting results were obtained using RGB imaging and NIR spectroscopy, particularly using portable NIR devices and specific digital cameras for in-field or in-mill monitoring. Nevertheless, it is important to highlight that RGB imaging and NIR spectroscopy need to be integrated with flesh hardness measurements, given the higher reliability of this parameter compared to olive skin color. Finally, with respect to EVOO, although several useful applications of visible imagining, UV–Visible, NIR, and Mid-Infrared spectroscopies have been found, the online monitoring of EVOO quality using NIR spectroscopy strikes us as being the most interesting technique for improving the EVOO production chain in the near future. Full article

Essential oil (EO) extraction is a widespread practice generating huge amounts of solid plant by-products a potential source of bioactive compounds, on the one hand, and a detrimental risk for the environment that needs to be carefully considered on the other hand. The present study aims to valorize Myrtus communis L. leaf by-products obtained following EO extraction using a steam distillation unit through the recovery of phenolic compounds and the evaluation of their biological activities. The total phenols, flavonoids, and proanthocyanidins contents of the ethanolic extract by-product were higher than the control (leaves without extraction of EO). Their amounts increased from 69.30 to 88.06 mg GAE/g for total phenols, from 36.31 to 70.97 mg QE for flavonoids and from 19.74 to 21.49 mg CE/g of extract for proanthocyanidins. The identification of phenolic compounds by high-performance liquid-chromatography equipped with a reversed-phase (RP-HPLC) system revealed that the by-product sample includes more gallic acid, catechin, syringic acid and luteolin 7-O-glucoside but less p-coumaric acid and kaempferol than the control. Moreover, the mid-infrared spectroscopy (MIR) showed the presence of benzene ring characteristic of phenolic compounds at 756 cm⁻¹, esters of aromatic acids and stretching vibrations of polyphenols at 1141–1234 cm⁻¹, C=C stretching present in phenolic acids such as coumaric acid and catechin at 1604 cm⁻¹. The assessment of antioxidant activity revealed that the ABTS^+• radical scavenging activity was significantly increased, whereas the DPPH^• radical inhibition activity and the ferric reduction antioxidant power were significantly decreased. The results indicated, as well, that Myrtus communis L. leaf by-products maintained a considerable antibacterial activity depending on the tested bacterial strain. Additionally, the anti-α-amylase activity was higher for the Myrtus communis L. leaf by-product extract. Therefore, Myrtus communis L. leaf by-products of EO extraction offer phenolic compounds with significant biological activities, contributing to the sustainable development and the promotion of circular economy by the recovery of valuable inputs from plant by-products. Full article

Er³⁺-doped fluorite crystals, including CaF₂ and SrF₂, are considered as attractive laser gain materials in the mid-infrared (MIR) region with merits of high laser efficiency as well as low doping concentration. In this work, a series of Er, La:CaF₂ crystals were grown and the modulation effect of co-doping La³⁺ ions on the spectral properties and mid-infrared laser performance was investigated. It was found that introducing La³⁺ ions can effectively manipulate the coordination environment of Er³⁺ ions embedded in CaF₂ crystal, thus modulating the shape and intensity of absorption and emission bands. On the other hand, La³⁺ ions can partially substitute Er³⁺ sites in the clusters to form mixed clusters, which affects the energy transfer processes between Er³⁺ ions as well as ~3 μm laser performance, which is dominated by energy transfer up-conversion (ETU) processes between Er³⁺ ions. By co-doping La³⁺ ions into Er:CaF₂ crystal at an appropriate concentration, the spectral parameter modulation can be achieved while maintaining a high MIR laser efficiency. Full article

Tunable laser spectroscopy (TLS) with infrared (IR) imaging is a powerful tool for gas leak detection. This study focuses on direct absorption spectroscopy (DAS) that utilizes wavelength modulation to extract gas information. A tunable interband cascade laser (ICL) with an optical power of 5 mW is periodically modulated by a sawtooth injection current at 10 Hz across the methane absorption around 3271 nm. A fast and sensitive thermal imaging camera for the mid-infrared range between 3 and 5.7 µm is operated at a frame rate of 470 Hz. Offline processing of image stacks is performed using different algorithms (DAS-F, DAS-f and DAS-2f) based on the Lambert–Beer law and the HITRAN database. These algorithms analyze various features of gas absorption, such as area (F), peak (f) and second derivative (2f) of the absorbance. The methane concentration in ppm*m is determined on a pixel-by-pixel analysis without calibration. Leak localization for methane leak rates as low as 0.25 mL/min is accurately displayed in a single concentration image with pixelwise sensitivities of approximately 1 ppm*m in a laboratory environment. Concentration image sequences represent the spatiotemporal dynamics of a gas plume with high contrast. The DAS-2f concept demonstrates promising characteristics, including accuracy, precision, 1/f noise rejection, simplicity and computational efficiency, expanding the applications of DAS. Full article

As the weak link in electro-optical imaging systems, photodetectors have always faced the threat of laser damage. In this paper, we experimentally investigated the damage mechanism of the photodetector induced by the out-of-band laser. The damage thresholds of the mid-infrared pulsed laser for Charge Coupled Device (CCD) and HgCdTe detectors were determined through damage experiments. The analysis of the damage phenomena and data for both CCD and HgCdTe detectors clearly demonstrated that out-of-band mid-infrared pulsed lasers could entirely incapacitate CCD and HgCdTe detectors. Our analysis of the damage process and data revealed that the primary mechanism of damage to CCD and HgCdTe detectors by mid-infrared pulsed lasers was primarily thermal. This study serves as a reference for further research on the mid-infrared pulsed laser damage mechanisms of CCD and HgCdTe detectors, as well as for laser protection and performance optimization in imaging systems. Full article

The integration of visual algorithms with infrared imaging technology has become an effective tool for industrial gas leak detection. However, existing research has mostly focused on simple scenarios where a gas plume is clearly visible, with limited studies on detecting gas in complex scenes where target contours are blurred and contrast is low. This paper uses a cooled mid-wave infrared (MWIR) system to provide high sensitivity and fast response imaging and proposes the MWIRGas-YOLO network for detecting gas leaks in mid-wave infrared imaging. This network effectively detects low-contrast gas leakage and segments the gas plume within the scene. In MWIRGas-YOLO, it utilizes the global attention mechanism (GAM) to fully focus on gas plume targets during feature fusion, adds a small target detection layer to enhance information on small-sized targets, and employs transfer learning of similar features from visible light smoke to provide the model with prior knowledge of infrared gas features. Using a cooled mid-wave infrared imager to collect gas leak images, the experimental results show that the proposed algorithm significantly improves the performance over the original model. The segment mean average precision reached 96.1% (mAP50) and 47.6% (mAP50:95), respectively, outperforming the other mainstream algorithms. This can provide an effective reference for research on infrared imaging for gas leak detection. Full article

Soil organic carbon (SOC) assessment is crucial for evaluating soil health and supporting carbon sequestration efforts. Traditional methods like wet digestion and dry combustion are time-consuming and labor-intensive, necessitating the development of non-destructive, cost-efficient, and real-time in situ measurements. This review focuses on handheld in situ methodologies for SOC estimation, underscoring their practicality and reasonable accuracy. Spectroscopic techniques, like visible and near-infrared, mid-infrared, laser-induced breakdown spectroscopy, and inelastic neutron scattering each offer unique advantages. Preprocessing techniques, such as external parameter orthogonalization and standard normal variate, are employed to eliminate soil moisture content and particle size effects on SOC estimation. Calibration methods, like partial least squares regression and support vector machine, establish relationships between spectral reflectance, soil properties, and SOC. Among the 32 studies selected in this review, 14 exhibited a coefficient of determination (R²) of 0.80 or higher, indicating the potential for accurate SOC content estimation using in situ approaches. Each study meticulously adjusted factors such as spectral range, pretreatment method, and calibration model to improve the accuracy of SOC content, highlighting both the methodological diversity and a continuous pursuit of precision in direct field measurements. Continued research and validation are imperative to ensure accurate in situ SOC assessment across diverse environments. Thus, this review underscores the potential of handheld devices for in situ SOC estimation with good accuracy and leveraging factors that influence its precision. Crucial for optimizing carbon farming, these devices offer real-time soil measurements, empowering land managers to enhance carbon sequestration and promote sustainable land management across diverse agricultural landscapes. Full article

An innovative payload containing a sensitive mid-wave infrared camera was flown on an uncrewed aircraft system (UAS) to acquire thermal imagery along a reach of the Sacramento River, California, USA. The imagery was used as input for an ensemble particle image velocimetry (PIV) algorithm to produce near-continuous maps of surface flow velocity along a reach approximately 1 km in length. To assess the accuracy of PIV velocity estimates, in situ measurements of flow velocity were obtained with an acoustic Doppler current profiler (ADCP). ADCP measurements were collected along pre-planned cross-section lines within the area covered by the imagery. The PIV velocities showed good agreement with the depth-averaged velocity measured by the ADCP, with $R^2$ values ranging from 0.59–0.97 across eight transects. Velocity maps derived from the thermal image sequences acquired on consecutive days during a period of steady flow were compared. These maps showed consistent spatial patterns of velocity vector magnitude and orientation, indicating that the technique is repeatable and robust. PIV of thermal imagery can yield velocity estimates in situations where natural water-surface textures or tracers are either insufficient or absent in visible imagery. Future work could be directed toward defining optimal environmental conditions, as well as limitations for mapping flow velocities based on thermal images acquired via UAS. Full article