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- Brno University of Technology
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- Southern Taiwan University of Science and Technology
- Institut National Polytechnique Felix Houphou?t-Boigny Yamoussoukro
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Resolving fine spectral features in lattice vibrational modes using femtosecond coherent spectroscopy
摘要： We show resolution of fine spectral features within several Raman active vibrational modes in potassium titanyl phosphate (KTP) crystal. Measurements are performed using a femtosecond time-domain coherent anti-Stokes Raman scattering spectroscopy technique that is capable of delivering equivalent spectral resolution of 0.1 cm?1. The Raman spectra retrieved from our measurements show several spectral components corresponding to vibrations of different symmetry with distinctly different damping rates. In particular, linewidths for unassigned optical phonon mode triplet centered at around 820 cm?1 are found to be 7.5±0.2 cm?1, 9.1±0.3 cm?1, and 11.2±0.3 cm?1. Results of our experiments will ultimately help to design an all-solid-state source for sub-optical-wavelength waveform generation that is based on stimulated Raman scattering.
关键词： damping rates,potassium titanyl phosphate,Raman active vibrational modes,femtosecond coherent spectroscopy,spectral resolution
更新于2025-09-23 15:21:01
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A novel spectral-spatial classification technique for multispectral images using extended multi-attribute profiles and sparse autoencoder
摘要： Image classification is a prominent topic and a challenging task in the field of remote sensing. Recently many various classification methods have been proposed for satellite images specifically the frameworks based on spectral-spatial feature extraction techniques. In this paper, a feature extraction strategy of multispectral data is taken into account in order to develop a new classification framework by combining Extended Multi-Attribute Profiles (EMAP) and Sparse Autoencoder (SAE). Extended Multi-Attribute Profiles is employed to extract the spatial information, then it is joined to the original spectral information to describe the spectral-spatial property of the multispectral images. The obtained features are fed into a Sparse Autoencoder as input. Finally, the learned spectral-spatial features are embedded into the Support Vector Machine (SVM) for classification. Experiments are conducted on two multispectral (MS) images such as we construct the ground truth maps of the corresponding images. Our approach based on EMAP and deep learning (DL), proves its huge potential to achieve a high classification accuracy in reasonable running time and outperforms traditional classifiers and others classification approaches.
关键词： Remote sensing,image classification,Extended Multi-Attribute Profiles,spectral-spatial feature extraction,Sparse Autoencoder,Support Vector Machine
更新于2025-09-23 15:21:01
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Spectral efficiency optimization for intelligent reflecting surface aided multi-input multi-output terahertz system
摘要： Intelligent reflecting surface (IRS) is considered as a promising application in terahertz (THz) communications since it is able to enhance the THz communication with no additional power consumptions. In this letter, we consider a downlink multi-input multi-output system, where a base station (BS) communicates to a user with the aid of the IRS. Our goal is to optimize the spectral efficiency by designing discrete phase-shifts at the IRS and the precoder at the BS, which is an intractable nonconvex optimization problem. To solve it, we approximate the problem into another form where we maximize the sum of path gains by designing the phase-shifts of the IRS, and we propose a cross-entropy based algorithm to search the optimal IRS phase-shifts matrix. After that, we use the classical singular value decomposition and water-filling solution to design the optimal precoder.
关键词： terahertz (THz) communication,intelligent reflecting surface (IRS),spectral efficiency
更新于2025-09-23 15:21:01
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Measurement setup for differential spectral responsivity of solar cells
摘要： We have developed a setup for measuring differential spectral responsivities of unifacial and bifacial solar cells under bias light conditions. The setup uses 30 high-brightness LEDs for generating a quasi-monochromatic light source covering the wavelength range 290–1300 nm. Halogen lamps are used to generate bias-lighting conditions up to the irradiance level of 1000 W/m2. The setup has been fully characterized for spectral irradiances and spatial uniformities of all light sources. Validation measurements carried out using a reference cell of 2 × 2 cm2 area from Fraunhofer ISE demonstrated an agreement better than 2% over the wavelength range of 425–940 nm, with an expanded uncertainty of 2.6%. In the UV and IR regions, the discrepancies are higher but still within estimated uncertainties. The setup is also tested in measuring spectral responsivities of large 15 × 15 cm2 bifacial solar cells. The associated problems are discussed.
关键词： Radiometry,Bifacial,Solar cell,Spectral responsivity,Electricity,Efficacy
更新于2025-09-23 15:21:01
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Calibration-free quantitative analysis of D/H isotopes with a fs-laser filament
摘要： The analytical characteristics of D/H isotopes with a fs-laser filament are investigated via analyzing a set of D-enriched water samples with D concentrations ranging from 0.5 to 20%. The filament emission spectra feature a narrow peak width and near-zero continuum spectral component. The characteristics of Balmer lines (a, b and g) are evaluated, and the Balmer-a line is selected for isotope analysis. Isotopic information is extracted from filament emission spectra through four different approaches: spectral deconvolution least squares algorithm (SDA), partial least squares regression-internal validation (PLSR-IV), partial least squares regression-cross validation (PLSR-CV) and partial least squares regression-calibration free (PLSR-CF). A multivariate spectral fitting procedure is established in the SDA. Fine structure components (FSCs) of Ha and Da were integrated in the SDA, and it shows improved analytical performance compared to the conventional SDA which is carried out by fitting the experimental spectra with two Lorentzian or Voigt functions. It is also found that the SDA with FSCs gives more accurate results than PLSR-IV and PLSR-CV. Furthermore, the analytical performance is significantly improved by the use of PLSR-CF, in which the PLSR calibration matrix is constructed with a synthetic spectra set. The improvement of accuracy for the given sample set further allows a calibration curve exhibiting an R2 exceeding 0.998 and a slop of 1.009. In addition, the calibration procedure with isotopically enriched standard samples is not necessary in PLSR-CF, demonstrating its flexibility over classical chemometric approaches.
关键词： fs-laser filament,PLSR,spectral deconvolution,calibration-free analysis,Balmer lines,D/H isotopes
更新于2025-09-23 15:21:01
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Laser Ignition and Flame Temperature for Low-Density Mixtures of Lignite Coal and Pentaerythritol Tetranitrate (Petn)
摘要： We have studied laser ignition (1064 nm, 120 μs) of mixtures of lignite coal (brown coal) particles of size ≤0.1 mm and pentaerythritol tetranitrate (PETN) additives. We established that as the amount of PTEN additives increases in the range 0–50 wt.%, the critical ignition energy density of the mixtures decreases monotonically from 2.9 to 2.0 J/cm2. We used spectral pyrometry to determine that the ?ame temperature for the mixture increases from 1800 K to 2100 K.
关键词： laser ignition,pentaerythritol tetranitrate (PETN),spectral pyrometry,lignite (brown coal),spectroscopy
更新于2025-09-23 15:21:01
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Multi-Spectral Water Index (MuWI): A Native 10-m Multi-Spectral Water Index for Accurate Water Mapping on Sentinel-2
摘要： Accurate water mapping depends largely on the water index. However, most previously widely-adopted water index methods are developed from 30-m resolution Landsat imagery, with low-albedo commission error (e.g., shadow misclassified as water) and threshold instability being identified as the primary issues. Besides, since the shortwave-infrared (SWIR) spectral band (band 11) on Sentinel-2 is 20 m spatial resolution, current SWIR-included water index methods usually produce water maps at 20 m resolution instead of the highest 10 m resolution of Sentinel-2 bands, which limits the ability of Sentinel-2 to detect surface water at finer scales. This study aims to develop a water index from Sentinel-2 that improves native resolution and accuracy of water mapping at the same time. Support Vector Machine (SVM) is used to exploit the 10-m spectral bands among Sentinel-2 bands of three resolutions (10-m; 20-m; 60-m). The new Multi-Spectral Water Index (MuWI), consisting of the complete version and the revised version (MuWI-C and MuWI-R), is designed as the combination of normalized differences for threshold stability. The proposed method is assessed on coincident Sentinel-2 and sub-meter images covering a variety of water types. When compared to previous water indexes, results show that both versions of MuWI enable to produce native 10-m resolution water maps with higher classification accuracies (p-value < 0.01). Commission and omission errors are also significantly reduced particularly in terms of shadow and sunglint. Consistent accuracy over complex water mapping scenarios is obtained by MuWI due to high threshold stability. Overall, the proposed MuWI method is applicable to accurate water mapping with improved spatial resolution and accuracy, which possibly facilitates water mapping and its related studies and applications on growing Sentinel-2 images.
关键词： MNDWI,OSH,SVM,AWEI,water mapping,water classification,shadow,NDWI,Sentinel-2,MuWI,Landsat,water index,multi-spectral water index,sunglint,machine learning
更新于2025-09-23 15:21:01
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Local Vaporization at the Cut Front at High Laser Cutting Speeds
摘要： High-speed videos of the cut front and spectrometric measurements were applied to detect local vaporization on the cut front at high cutting speeds to show that with increasing feed rate, temporally short and intense flashes are generated by vaporization phenomena on the upper part of the cut front. The latter are accompanied by the emergence of an interrupted striation pattern on the surface of the cutting edge. The findings support the assumption that local vaporization at the cut front might be the cause for reduced quality of the cutting process at elevated cutting speeds. The observation of vaporization serves as a diagnostic method to anticipate a fail cut and the interrupted striation pattern.
关键词： Laser cutting,Vaporization,Interrupted striations,Camera observation,Spectral emission
更新于2025-09-23 15:21:01
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Nonresonant Polarized Raman Spectra Calculations of Nitrogen-Doped Single-Walled Carbon Nanotubes: Diameter, Chirality, and Doping Concentration Effects
摘要： Raman spectra of nitrogen-doped single-walled carbon nanotubes are calculated using the spectral moment’s method combined with the bond polarizability model. The influence of the nanotube diameter and chirality is investigated. We also address the important question of the effect of the N-doping concentration, and we propose an equation to estimate the doping concentration from the knowledge of the tube diameter and the frequency of the radial breathing mode.
关键词： spectral moment’s method,Raman spectra,N-doping concentration,nanotube diameter,nitrogen-doped single-walled carbon nanotubes,bond polarizability model,chirality
更新于2025-09-23 15:21:01
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Nonlinear Optics || Ultrafast and Intense-Field Nonlinear Optics
摘要： There is currently great interest in the physics of ultrashort laser pulses. Recent advances have led to the generation of laser pulses with durations of the order of 1 attosecond (Hentschel et al., 2001). Ultrashort pulses can be used to probe the properties of matter on extremely short time scales. Within the context of nonlinear optics, ultrashort laser pulses are of interest for at least two separate reasons. The ?rst reason is that the nature of nonlinear optical interactions is often profoundly modi?ed through the use of ultrashort laser pulses, in part because of the broad spectral bandwidth necessarily associated with such pulses. The next two sections of this chapter treat various aspects of the resulting modi?cations of the nature of nonlinear optical interactions. The second reason is that ultrashort laser pulses tend to possess extremely high peak intensities (because laser pulse energies tend to be established by the energy-storage capabilities of laser gain media), and thus short laser pulses tend to have much higher peak powers than longer pulses. The second half of this chapter is devoted to a survey of the sorts of nonlinear optical processes that can be excited by extremely intense laser ?elds.
关键词： attosecond pulses,ultrashort laser pulses,high peak intensities,spectral bandwidth,nonlinear optics
更新于2025-09-23 15:21:01