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Investigation of GaAsBi epitaxial layers for THz emitters pumped by long-wavelength fiber lasers
摘要： Herein we report the studies on the GaBiAs terahertz emitters. The molecular beam epitaxy grown thin films were subjected to structural and optical characterization. Inhomogeneity of Bi concentration in the samples is confirmed by XRD, PL and EDS studies. Investigations on the generation characteristics of the fabricated bow-tie photoconductive antennas were carried out via the Fourier Transform Infrared Spectroscopy. The collected data indicate a pattern of change in the shape of the spectra with increasing bismuth concentration, namely, a sharp drop in the low-frequency part (0.1–0.2 THz) simultaneously with a noticeable increase in intensity in the range 0.3–1 THz with a pronounced maximum at frequencies of ~0.4 THz. The deterioration of the THz power to average photocurrent ratio can be explained by a general decrease in the electron mobility, caused both by a large number of structural defects and by a large local heating of the crystal.
关键词： terahertz emitters,photoconductive antennas,molecular beam epitaxy,GaBiAs,Fourier Transform Infrared Spectroscopy
更新于2025-09-23 15:19:57
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Reduced Nonradiative Voltage Loss in Terpolymer Solar Cells
摘要： The dissociation of hybrid local-charge transfer excitons (LE-CT) in efficient bulk-heterojunction non-fullerene solar cells contributes to reduced non-radiative photovoltage loss, a mechanism that still remains unclear. Herein, we studied the energetic and entropic contribution in the hybrid LE-CT exciton dissociation in devices based on a conjugated terpolymer. Compared to reference devices based on ternary blends, the terpolymer devices demonstrated a significant reduction of the non-radiative photovoltage loss, regardless of the acceptor molecule, be it fullerene or non-fullerene. Fourier transform photocurrent spectroscopy revealed a significant LE-CT character in the terpolymer-based non-fullerene solar cells. Temperature-dependent hole mobility and photovoltage confirm that entropic and energetic effects contribute to the efficient LE-CT dissociation. The energetic disorder value measured in the fullerene- or nonfullerene-based terpolymer devices suggested that this entropic contribution came from the terpolymer, a signature of higher disorder in copolymers with multiple aromatic groups. This gives new insight into the fundamental physics of efficient LE-CT exciton dissociation with smaller non-radiative recombination loss.
关键词： non-radiative photovoltage loss,terpolymer solar cells,entropic and energetic effects,hybrid local-charge transfer excitons,Fourier transform photocurrent spectroscopy
更新于2025-09-23 15:19:57
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Grain Boundary Induced Ultralow Threshold Random Laser in a Single GaTe Flake
摘要： Random lasing is a lasing phenomenon realized in random media, and has attracted a great deal of attention in recent years. An essential requirement for strong random lasing is to achieve strong and recurrent scattering among grain boundaries of a disordered structure. Herein, we report a random laser (RL) based on individual polycrystalline GaTe microflakes (MFs) with a lasing threshold of 4.15 kW cm-2, about 1-2 orders of magnitude lower than that of the reported single GaN microwire random laser. The strongly enhanced light scattering and trapping benefit from the reduced grain size in the polycrystalline GaTe MF, resulting in a ultralow threshold. We also investigate the dependence of spatially localized cavities’ dimension on the pumping intensity profile and temperature. The findings provide a feasible route to realize RL with low threshold and small size, opening up a new avenue in fulfilling many potential optoelectronic applications of RL.
关键词： fast Fourier-transform,random laser,GaTe,ultralow-threshold,grain-boundary
更新于2025-09-23 15:19:57
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Multiple Input Single Output Phase Retrieval
摘要： In this paper, we consider the problem of recovering the phase information of multiple sources from a mixed phaseless short-time Fourier transform measurement, which is called multiple input single output (MISO) phase retrieval problem. It is an inherently ill-posed problem due to the lack of the phase and mixing information, and the existing phase retrieval algorithms are not explicitly designed for this case. To address the MISO phase retrieval problem, a least-squares method coupled with an independent component analysis (ICA) algorithm is proposed for the case of sufficiently long window length. When these conditions are not met, an integrated algorithm is presented, which combines a gradient descent algorithm by minimizing a non-convex loss function with an ICA algorithm. Experimental evaluation has been conducted to show that under appropriate conditions the proposed algorithms can explicitly recover the signals, the phases of the signals, and the mixing matrix. In addition, the algorithm is robust to noise.
关键词： Short-time Fourier transform (STFT),Multiple input single output (MISO),Independent component analysis (ICA),Non-convex optimization,Phase retrieval
更新于2025-09-19 17:15:36
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Radial-profile-customized orbital-angular-momentum modes: Featuring tailored Gaussian intensity pattern at target receiving plane
摘要： We present the modified-Bessel-superposed Gaussian (MBSG) orbital-angular-momentum (OAM) modes, which can evolve into a field featuring a tailored Gaussian amplitude profile after propagating to a target receiving plane. Analytical expressions for the MBSG OAM modes at a source plane are developed in both the space and wavevector domains. The space- and wavevector-domain representations of the MBSG OAM modes at the source plane are found to share a mathematically formal similarity. We propose to utilize this appealing property for designing a Fourier-transform-based approach to forming the MBSG OAM modes at the source plane. Unlike other commonly reported OAM modes, the receiving-plane field of MBSG OAM modes always exhibits a customized non-ring-shaped Gaussian intensity pattern. This behavior can be exploited, e.g., to benefit the projective phase-flattening OAM measurement and to reduce the turbulence-induced OAM-mode scattering in relevant practical applications.
关键词： Fourier transform,Orbital angular momentum,Optical vortex,Spiral phase front
更新于2025-09-19 17:15:36
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Electromagnetic fields produced by a swift electron: A source of white light
摘要： In this work we calculate the electromagnetic fields generated by a swift electron in both time and frequency domains. Although the electromagnetic fields in the time domain produced by a bare fast electron are obtained in standard textbooks, their time Fourier transform is not satisfactorily discussed neither are the integrals involved in the computation of it. We show that care must be taken when calculating the electromagnetic fields in the frequency domain to preserve their real nature.
关键词： Fourier transform,Relativistic electrons,Electromagnetic fields.
更新于2025-09-19 17:15:36
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Digital Staining of High-Definition Fourier Transform Infrared (FT-IR) Images Using Deep Learning
摘要： Histological stains, such as hematoxylin and eosin (H&E), are routinely used in clinical diagnosis and research. While these labels offer a high degree of specificity, throughput is limited by the need for multiple samples. Traditional histology stains, such as immunohistochemical labels, also rely only on protein expression and cannot quantify small molecules and metabolites that may aid in diagnosis. Finally, chemical stains and dyes permanently alter the tissue, making downstream analysis impossible. Fourier transform infrared (FT-IR) spectroscopic imaging has shown promise for label-free characterization of important tissue phenotypes and can bypass the need for many chemical labels. Fourier transform infrared classification commonly leverages supervised learning, requiring human annotation that is tedious and prone to errors. One alternative is digital staining, which leverages machine learning to map IR spectra to a corresponding chemical stain. This replaces human annotation with computer-aided alignment. Previous work relies on alignment of adjacent serial tissue sections. Since the tissue samples are not identical at the cellular level, this technique cannot be applied to high-definition FT-IR images. In this paper, we demonstrate that cellular-level mapping can be accomplished using identical samples for both FT-IR and chemical labels. In addition, higher-resolution results can be achieved using a deep convolutional neural network that integrates spatial and spectral features.
关键词： convolutional neural networks,FT-IR,deep learning,Fourier transform infrared,histopathology,Histology,classification,digital staining
更新于2025-09-19 17:15:36
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High-speed 3D shape measurement using Fourier transform and stereo vision
摘要： Background: In the fast 3D shape measurement, it is an important factor to use the least number of fringe patterns to get the wrapped phase and the wrapped phase is always required to be retrieved to absolute phase. But the process of phase unwrapping may affect the quality of absolute phase. Besides absolute phase retrieval is time-costing especially for high-speed 3D shape measurement. Methods: This paper proposes a fast measurement method based on Fourier transform profilometry and stereo vision. Because of the property of stereo vision, every point can find its corresponding point in the wrapped phase. This method can reconstruct 3D surface without phase unwrapping. In order to further increase the measurement speed and overcome the gamma effect of projector, the dithering fringe pattern is used. To resist false matching, the original image matching constraint gives a rough parallax. Phase matching and sub-pixel parallax optimization are used to reduce the matching errors. In order to confirm the phase value of points which are at the edge of wrapped phase, average phase value is calculated. Results: A white mask is measured based on the proposed method. The results from every step show the effect of different functions. To better show the effect of the proposed method, a white house is measured and the measurement is compared with LSSM and MFH. In order to further to show the advantage of the proposed method, discontinuous blocks and continuous blocks are measured. The average height, RMS, average error, maximum error are compared with the method which uses absolute phase to match the corresponding points. Experiment results verify the feasibility of the proposed method and it can measure complex objects with high speed and accuracy. Conclusion: This paper uses Fourier transform and stereo vision to get wrapped phase and reconstruct 3D shape without phase unwrapping. The proposed method contains three part: phase matching, edge points detection and sub-pixel parallax optimization. By comparing matching precision, the proposed method can get high quality surface. Because the process of measurement only need one frame of deformed fringe pattern to get the wrapped phase and the matching process does not need phase unwrapping, the proposed method has the potential to be used in fast measurement.
关键词： Fourier transform,Three-dimensional shape measurement,Stereo vision,Fringe analysis
更新于2025-09-19 17:15:36
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Optimisation of the Quantification of Total Soluble Solids, pH and Titratable Acidity in South African Grape Must using Fourier Transform Mid-infrared Spectroscopy
摘要： Calibration models for Fourier transform mid-infrared (FT-MiR) spectroscopy were developed for the simultaneous quantification of total soluble solids (TSS, measured as °Brix), pH and titratable acidity (TA, expressed as g/L tartaric acid) in South African (SA) grape must. An exploratory data analysis of the FT-MIR spectra of 1170 grape must samples (647 for °Brix, 252 for pH and 271 for TA) was done by principal component analysis, and partial least squares regression was used for the computation of the regression models. The prediction errors for TSS (0.34 °Brix), pH (0.04 units) and TA (0.51 g/L) provided analytical data of satisfactory accuracy. The evaluation of ready-to-use global calibrations to quantify these three parameters in SA samples presented standard error of prediction (SEP) values of 0.46°Brix, 0.10 pH units and 3.13 g/L for TA. After slope and intercept adjustments of the original global calibration algorithms, the SEP values were reduced to 0.38 °Brix, 0.05 pH units and 0.49 g/L for TA. These results show the necessity for optimisation of the global FT-MIR WineScan calibrations to provide a better fit to samples of South African origin. The results demonstrate that FT-MiR spectroscopy is a useful technique for the rapid quantification of major grape must parameters and for quality control purposes in an industrial cellar.
关键词： wine grape chemical analysis,Fourier transform infrared spectroscopy,chemometrics
更新于2025-09-19 17:15:36
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Interaction of Zinc Oxide and Copper Oxide Nanoparticles with Chlorophyll: A Fluorescence Quenching Study
摘要： The present study aims to investigate the interactions of zinc oxide nanoparticles and copper oxide nanoparticles with the major photosynthetic pigment chlorophyll using ultraviolet-visible, steady state, and time resolved laser induced fluorescence spectroscopy. The steady state fluorescence measurements show that zinc oxide and copper oxide nanoparticles quench the fluorescence of chlorophyll in concentration-dependent manner. The Stern-Volmer plot for the chlorophyll-zinc oxide nanoparticles is linear, and the value of quenching constant has been observed to increase with temperature indicating the possibility of dynamic quenching. A decrease in the lifetime of chlorophyll with increase in the concentration of zinc oxide nanoparticles confirms the involvement of dynamic quenching in the chlorophyll–zinc oxide nanoparticle interaction. In the case of copper oxide nanoparticles, the Stern-Volmer plot deviates from linearity observed in the form of upward curvature depicting the presence of both static and dynamic quenching. In addition, the lifetime of chlorophyll decreases with increase in the concentration of copper oxide nanoparticles displaying the dominance of dynamic quenching in the chlorophyll-copper oxide nanoparticle interaction. The decrease observed in the value of binding constant with increasing temperature and negative values of change in enthalpy, entropy, and Gibb’s free energy indicates that van der Waal and hydrogen bonding are the prominent forces during the interaction of chlorophyll with both zinc oxide and copper oxide nanoparticles and that the process is spontaneous and exothermic. The interaction of zinc oxide and copper oxide nanoparticles with chlorophyll occurs through electron transfer mechanism. The obtained results are useful in understanding the sensitization processes involving chlorophyll and zinc oxide and copper oxide nanoparticles.
关键词： chlorophyll and nanoparticles,molecular interaction,ultraviolet-visible spectroscopy,laser-induced fluorescence spectroscopy,Attenuated total reflectance–Fourier transform infrared spectroscopy,steady state and time resolved fluorescence,X-ray diffraction
更新于2025-09-19 17:15:36