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Measurement of ultrafast dynamics of photoexcited carriers in <i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> by two-color optical pump-probe spectroscopy
摘要： We report results from ultrafast two-color optical pump-probe spectroscopy on bulk b-Ga2O3. A two-photon absorption scheme is used to photoexcite carriers with the pump pulse and free-carrier absorption of the probe pulse is used to record the subsequent dynamics of the photoexcited carriers. Our results are consistent with carrier recombination via defect-assisted processes. We also observe transient polarization-selective optical absorption of the probe pulse by defect states under nonequilibrium conditions. A rate equation model for electron and hole capture by defects is proposed and used to explain the data. Whereas the rate constants for electron capture by defects are found to be temperature-independent, they are measured to be strongly temperature-dependent for hole capture and point to a lattice deformation/relaxation process accompanying hole capture. Our results shed light on the mechanisms and rates associated with carrier capture by defects in b-Ga2O3.
关键词： two-color optical pump-probe spectroscopy,ultrafast dynamics,photoexcited carriers,carrier recombination,defect-assisted processes,β-Ga2O3
更新于2025-09-04 15:30:14
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Development of a radiative transfer model for the determination of toxic gases by Fourier transform–infrared spectroscopy with a support vector machine algorithm
摘要： This report describes a radiative transfer model for Fourier transform-infrared (FT-IR) spectroscopy to create close-to-reality toxic gas spectra by reflecting the unique spectral responses of detectors and using the atmospheric radiative transfer code, MODTRAN. This system can be highly useful in overcoming the limitations for measuring toxic gases in open environments. The emulated gas spectra can be used to train support vector machine (SVM) for chemical gas detection. Its detection performance is evaluated with nerve agents (tabun, sarin, soman, and cyclosarin) and a simulant gas (sulfur hexafluoride) for indoor and outdoor experiments by using two off-the-shelf FT-IR gas detectors. The experimental results show that the proposed SVM algorithm successfully detected and classified targeted gases while reducing false negative and false positive detection rates.
关键词： support vector machine gas detection,Fourier transform infrared remote sensing,support vector machine,hyperspectral imaging,Fourier transform – infrared spectroscopy,stand-off detection
更新于2025-09-04 15:30:14
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Near-infrared Zeeman spectroscopy for the spatially resolved measurement of helium emission spectra in Heliotron J
摘要： A passive spectroscopic method that can measure spatially resolved emission spectra only by observing from a single diagnostic port without assuming plasma symmetry was applied to the stellarator-heliotron device Heliotron J. The emission spectra from the inboard and outboard sides were separated using the difference in their Zeeman effects. On the basis of the fact that in a spectrum as a function of the wavelength, the magnitude of the wavelength splitting by the Zeeman effect relative to the Doppler broadening increases with the wavelength, the method was applied to a near-infrared helium emission line (He I 1s2s 3S?1s2p 3P, 1083 nm), and it was confirmed that the uncertainty in the separated spectra was reduced compared with that in the application to visible emission lines. From the emissivity of the separated spectra, the local recycling flux was evaluated using the inverse photon efficiency method.
关键词： Zeeman effect,plasma surface interaction,stellarator,recycling,plasma spectroscopy,tomography
更新于2025-09-04 15:30:14
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Raman spectroscopy for kidney tissue and its neoplasms research
摘要： This work is devoted to the study of the spectral properties of intact and tumor kidney tissues. For excitation of Raman scattering and autofluorescence a laser with a wavelength of 785 nm was used. Visually and morphologically unchanged tissues of pig and human kidneys as well as tumor tissue of human kidneys were used as the test samples. The analysis of registered signals was carried out using the method of projection on latent structures to isolate the spectral features between tissue types. The study showed a difference between the registered signals of the clear cell adenocarcinoma and chromophobe types of human kidney cancer, the most informative bands of the Raman spectrum for the determination of the clear cell human kidney cancer were 330-500 cm-1, 870-980 cm-1, 980-1130 cm-1, 1230-1270 cm-1, 1360 -1420 cm-1.
关键词： spectral properties,autofluorescence,neoplasms,kidney tissue,Raman spectroscopy
更新于2025-09-04 15:30:14
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Investigation of gas discharge features during HiPIMS using optical emission spectroscopy
摘要： The paper presents the results of the investigation of the emission spectra of a gas discharge during high-power impulse magnetron sputtering (HiPIMS) of a titanium target at different power supply parameters. In such mode, the fraction of ionized atoms of the target material in the discharge increases significantly, what affects the properties of the deposited coatings. The characteristic features of the operation of the system in HiPIMS mode were singled out, and also the discharge spectra were compared at high-power impulse and conventional (sputtering on a direct current) operation modes of the magnetron. As a result of the study, it was shown that the use of optical emission spectroscopy during HiPIMS makes it possible to effectively determine the parameters of the stable operation of the system and determine the boundary at which a transition into high-power regime occurs.
关键词： titanium target,HiPIMS,gas discharge,magnetron sputtering,optical emission spectroscopy
更新于2025-09-04 15:30:14
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Room-Temperature Continuous-Wave Frequency-Referenced Spectrometer up?to?7.5?THz
摘要： The lack of coherent room-temperature sources in the whole terahertz spectral window (0.3–10 THz) has significantly hampered the growth of scientific and technological applications in this range. Among them, high-precision frequency measurements of molecular transitions play a central role but remain an open challenge. Here, room-temperature generation and detection of continuous-wave, broadly tunable, narrow-linewidth THz radiation are presented, and their application to high-resolution spectroscopy in the broad 1–7.5 THz spectral range is demonstrated. This result has been achieved by implementing a Cherenkov phase-matching scheme into a channel waveguide in a nonlinear crystal. This simple approach, entirely based on robust telecom technology, unprecedently merges in a single source an ultra-broad continuous-wave spectral coverage and a state-of-the-art accuracy (approximately 10?9) in molecular-transition-center determination.
关键词： terahertz,continuous-wave,frequency-referenced,spectroscopy,Cherenkov phase-matching
更新于2025-09-04 15:30:14
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Quantitative Determination of Fluorine Content in Blends of Polylactide (PLA)–Talc Using Near Infrared Spectroscopy
摘要： Near-infrared spectroscopy (NIRS) has been widely used for quantitative and/or qualitative determination of a wide range of matrices. The objective of this study was to develop a NIRS method for the quantitative determination of fluorine content in polylactide (PLA)-talc blends. A blending profile was obtained by mixing different amounts of PLA granules and talc powder. The calibration model was built correlating wet chemical data (alkali digestion method) and NIR spectra. Using FT (Fourier Transform)-NIR technique, a Partial Least Squares (PLS) regression model was set-up, in a concentration interval of 0 ppm of pure PLA to 800 ppm of pure talc. Fluorine content prediction (R2 cal = 0.9498; standard error of calibration, SEC = 34.77; standard error of cross-validation, SECV = 46.94) was then externally validated by means of a further 15 independent samples (R2 EX.V = 0.8955; root mean standard error of prediction, RMSEP = 61.08). A positive relationship between an inorganic component as fluorine and NIR signal has been evidenced, and used to obtain quantitative analytical information from the spectra.
关键词： quantitative calibration,fluorine,PLA,polylactide,blends,talc,near infrared spectroscopy
更新于2025-09-04 15:30:14
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Characterization of dielectric properties and conductivity in encapsulation materials with high insulating filler contents
摘要： The properties of different molding-compound materials with high filler contents have been investigated in order to assess their electrical properties. The experimental part of the present work has been focused on dielectric spectroscopy and steady-state conduction measurements. The results have been used to investigate the electrical properties of the materials at different frequencies, temperatures and electric fields. Differences in the relaxation kinetics with increasing filler content have been found, which can be ascribed to the larger interface regions between the filler particles. In addition, the extracted conductivities show a hopping transport and different activation energies on the temperature range from 20 oC to 190 oC.
关键词： dielectric polarization,epoxy resins,spectroscopy
更新于2025-09-04 15:30:14
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Fluorescence enhancement of a microbial rhodopsin via electronic reprogramming
摘要： The engineering of microbial rhodopsins with enhanced fluorescence is of great importance in the expanding field of optogenetics. Here we report the discovery of two mutants (W76S/Y179F and L83Q) of a sensory rhodopsin from the cyanobacterium Anabaena PCC7120 with opposite fluorescence behavior. In fact, while W76S/Y179F displays, with respect to the wild-type protein, a nearly ten-fold increase in red-light emission, the second is not emissive. Thus, the W76S/Y179F, L83Q pair offers an unprecedented opportunity for the investigation of fluorescence enhancement in microbial rhodopsins, which is pursued by combining transient absorption spectroscopy and multi-configurational quantum chemistry. The results of such an investigation point to an isomerization-blocking electronic effect as the direct cause of instantaneous (sub-picosecond) fluorescence enhancement.
关键词： fluorescence enhancement,multi-configurational quantum chemistry,transient absorption spectroscopy,optogenetics,electronic reprogramming,microbial rhodopsins
更新于2025-09-04 15:30:14
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XPS investigation of F-doped MnO <sub/>2</sub> nanosystems fabricated by plasma assisted-CVD
摘要： Supported Mn(IV) oxide nanomaterials were prepared by plasma assisted-chemical vapor deposition from Ar/O2 plasmas starting from a fluorinated Mn(II) β-diketonate diamine adduct. Under the adopted conditions, the target compound served as a single-source molecular precursor for the obtainment of MnO2 nanosystems uniformly doped with fluorine. The overall F content in the target materials, composed of phase-pure β-MnO2, could be tailored as a function of the deposition temperature from 100 to 400 °C, a result of particular importance in view of photocatalytic and gas sensing applications. In the present study, attention is specifically devoted to the investigation of a representative specimen by means of x-ray photoelectron spectroscopy. Besides the wide scan spectrum, a detailed analysis of C 1s, O 1s, Mn 2p, Mn 3s, and F 1s photoelectron peaks is presented and discussed. The analyses reveal the formation of MnO2 free from other manganese oxides, with fluorine present in different chemical states, i.e., lattice F plus traces of precursor residuals at the system surface.
关键词： fluorine doping,x-ray photoelectron spectroscopy,PA-CVD,manganese oxide
更新于2025-09-04 15:30:14