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Simplification and experimental investigation of geometrical surface smoothness model for multi-track laser cladding processes
摘要： The formation of large area parts requires construction of multi-track laser cladding layers which are significantly influenced by the overlapping coefficient. The geometrical model of optimal overlap ratio to obtain least surface fluctuation of multi-track claddings is derived into a simpler form in terms of the aspect ratio of single-track clads. The error analysis further demonstrates the effectiveness of these models. Multi-track single layer claddings are fabricated at a series of overlap ratios under two process conditions. The surface states of cladding layers are then evaluated by two types of smoothness definitions with two fitting methods to study the optimal overlap ratios. The results show that the experimental optimum conditions identified by two methods are slightly different from each other. The theoretical prediction is in good agreement with the experimental one when the aspect ratio is great enough to support the model assumptions.
关键词： Laser cladding,Multi-track clads,Overlap ratio,Geometrical model,Surface smoothness
更新于2025-11-28 14:24:20
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Dual-wavelength thulium/holmium-doped fiber laser generation in 2 <i>μ</i> m region with high side-mode suppression ratio
摘要： We demonstrate a dual-wavelength laser with emission in the 2 μm wavelength region using a thulium/holmium co-doped fiber and a non-adiabatic tapered fiber as a comb filter. The configuration employed a backward pumping scheme and dual-wavelength laser was generated at 2023.53 and 2032.82 nm. The side-mode suppression ratio (SMSR) is more than 44 dB with overall good stability performance. The proposed configuration presents a simple yet practical scheme of generating 2 μm dual-wavelength laser with good SMSR. This investigation may offer a more efficient yet eye safe dual-wavelength related applications for end users.
关键词： comb filter,tapered fiber,side-mode suppression ratio,thulium/holmium-doped fiber laser,dual-wavelength laser
更新于2025-11-28 14:23:57
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Up-Converting Lanthanide Fluoride Core@Shell Nanorods for Luminescent Thermometry in the First and Second Biological Windows - β-NaYF4: Yb3+, Er3+@SiO2 Temperature Sensor
摘要： Up-converting core@shell type β-NaYF4:Yb3+-Er3+@SiO2 nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λex= 975 nm), i.e. up-conversion luminescence of Er3+ and down-shifting emission of Yb3+, located in the first (I-BW) and the second (II-BW) biological windows of the spectral range. The intensity ratios of the emission bands of Er3+ and Yb3+ observed in the Vis-NIR range monotonously change with temperature, i.e. the thermalized Er3+ levels (2H11/2→4I15/2/4S3/2→4I15/2) and the non-thermally coupled Yb3+/Er3+ levels (2F5/2→2F7/2/4I9/2→4I15/2 or 4F9/2→4I15/2). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and 2-th order polynomial fits for temperature sensing purposes, i.e. Er3+ 525/545 nm (max Sr = 1.31 %K-1) and Yb3+/Er3+ 1010/810 nm (1.64 %K-1) or 1010/660 nm (0.96 %K-1). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb3+/Er3+ bands, vs. the typically used Er3+ 525/545 nm band ratio, i.e. better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range Vis-NIR optical, contactless sensors of temperature.
关键词： Up-conversion luminescence,Luminescence intensity ratio (LIR),Functional nanomaterials,Rare earth ions,Energy transfer,Optical thermometer
更新于2025-11-25 10:30:42
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Single-cell redox states analyzed by fluorescence lifetime metrics and tryptophan FRET interaction with NAD(P)H
摘要： Redox changes in live HeLa cervical cancer cells after doxorubicin treatment can either be analyzed by a novel fluorescence lifetime microscopy (FLIM)-based redox ratio NAD(P)H-a2%/FAD-a1%, called fluorescence lifetime redox ratio or one of its components (NAD(P)H-a2%), which is actually driving that ratio and offering a simpler and alternative metric and are both compared. Auto-fluorescent NAD(P)H, FAD lifetime is acquired by 2- photon excitation and Tryptophan by 3-photon, at 4 time points after treatment up to 60 min demonstrating early drug response to doxorubicin. Identical Fields-of-view (FoV) at each interval allows single-cell analysis, showing heterogeneous responses to treatment, largely based on their initial control redox state. Based on a discrete ROI selection method, mitochondrial OXPHOS and cytosolic glycolysis are discriminated. Furthermore, putative FRET interaction and energy transfer between tryptophan residue carrying enzymes and NAD(P)H correlate with NAD(P)H-a2%, as does the NADPH/NADH ratio, highlighting a multi-parametric assay to track metabolic changes in live specimens.
关键词： Fluorescence Lifetime Imaging Microscopy (FLIM),single-cell analysis,NADPH/NADH ratio,NAD(P)H,redox,FAD,fluorescence lifetime redox ratio (FLIRR),NAD(P)H-a2%
更新于2025-11-21 11:24:58
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Optimized signal-to-noise ratio with shot noise limited detection in Stimulated Raman Scattering microscopy
摘要： We describe our set-up for Stimulated Raman Scattering (SRS) microscopy with shot noise limited detection for a broad window of biologically relevant laser powers. This set-up is used to demonstrate that the highest signal-to-noise ratio (SNR) in SRS with shot noise limited detection is achieved with a time-averaged laser power ratio of 1:2 of the unmodulated and modulated beam. In SRS, two different coloured laser beams are incident on a sample. If the energy difference between them matches a molecular vibration of a molecule, energy can be transferred from one beam to the other. By applying amplitude modulation to one of the beams, the modulation transfer to the other beam can be measured. The efficiency of this process is a direct measure for the number of molecules of interest in the focal volume. Combined with laser scanning microscopy, this technique allows for fast and sensitive imaging with sub-micrometre resolution. Recent technological advances have resulted in an improvement of the sensitivity of SRS applications, but few show shot noise limited detection. The dominant noise source in this SRS microscope is the shot noise of the unmodulated, detected beam. Under the assumption that photodamage is linear with the total laser power, the optimal SNR shifts away from equal beam powers, where the most signal is generated, to a 1:2 power ratio. Under these conditions the SNR is maximized and the total laser power that could induce photodamage is minimized. Compared to using a 1:1 laser power ratio, we show improved image quality and a signal-to-noise ratio improvement of 8 % in polystyrene beads and C. Elegans worms. Including a non-linear damage mechanism in the analysis, we find that the optimal power ratio converges to a 1:1 ratio with increasing order of the non-linear damage mechanism.
关键词： shot noise limited detection,signal-to-noise ratio,Nonlinear Raman microscopy
更新于2025-11-21 11:08:12
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Detection of Tetracycline in Water Using Glutathione-protected Fluorescent Gold Nanoclusters
摘要： Tetracycline (Tc), a widely used antibiotic, is one of the major pollutants in water. Herein, glutathione (GSH)-protected Au nanoclusters (GSH-AuNCs) were prepared to detect Tc. The fluorescence quenching ratio of GSH-AuNCs shows an excellent linear response against tetracycline in the concentration range of 50 μg/L – 50 mg/L with the detection limit of 5.31 μg/L. For the test paper prepared by GSH-AuNCs, 1 mg/L Tc caused a significant difference that could be recognized by the naked eye. The method exhibited good selectivity and excellent recovery when applied to a tap water sample. The method has the potential for Tc detection in real samples.
关键词： tetracycline detection,Au nanocluster,glutathione,recovery experiment,quenching ratio
更新于2025-11-19 16:56:35
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Estimation of syringyl units in wood lignins by FT-Raman spectroscopy
摘要： Syringyl (S) lignin content and syringyl-to-guaiacyl (S/G) lignin ratio are important characteristics of wood and lignocellulosic biomass. Although numerous methods are available for estimating S lignin units and S/G ratio, in this work, a new method based on Raman spectroscopy that uses the 370 cm-1 Raman band-area intensity (370-area) was developed. The reliability of the Raman approach for determining S content was first tested by the quantitative analysis of three syringyl lignin models by sampling them, separately, in dioxane and in Avicel. Good linear correlations between the 370 cm-1 intensity and model concentrations were obtained. Next, the %S lignin units in various woods were measured by correlating the 370 cm-1 Raman intensity data with values of S units in lignin determined by three regularly used methods – thioacidolysis, DFRC, and 2D-HSQC NMR. The former two methods take into account only the monomers cleaved from β–O–4-linked lignin units whereas the NMR method reports S content on the whole cell wall lignin. When the 370-area intensities and %S values from the regularly used methods were correlated, good linear correlations were obtained (R2 = 0.767, 0.731, and 0.804, respectively, for the three methods). The correlation with the highest R2, i.e., with the 2D NMR method, is being proposed for estimating S units in wood lignins by Raman spectroscopy as, in principle, both represent of the whole cell wall lignin and not just the portion of lignin that gets cleaved to release monomers. The Raman analysis method is quick, uses minimal harmful chemicals, carried out nondestructively, and is insensitive to the wet or dry state of the sample. The only limitations are that a sample of wood contain at least 30% S and not be significantly fluorescent, although the latter can be mitigated in some cases.
关键词： NMR,Cell wall,%S,Thioacidolysis,S/G ratio,DFRC
更新于2025-11-14 15:16:37
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Temperature sensitive properties of Eu2+/Eu3+ dual-emitting LaAlO3 phosphors
摘要： In this study, Eu2+/Eu3+ coexisting perovskite LaAlO3 phosphors were synthesized by a traditional high-temperature solid-phase reaction method and investigated via X-ray diffraction data, X-ray photoelectron spectroscopy and temperature-dependent photoluminescence spectra. The Eu2+/Eu3+ coexisting LaAlO3 phosphors exhibit excellent optical temperature sensing characteristics and are potential inorganic materials for temperature detection. The measured maximal absolute temperature sensitivity reaches 0.014 K-1, and the corresponding largest relative temperature sensitivity is 1.193% K-1, which are superior to most of previous reports of that. Meanwhile, the monitored signal peaks are well separated, providing a good signal discriminability. The energy level crossover relaxation of Eu2+ and Struck-Fonger crossover process involving O2–-Eu3+ charge transfer band were used to explain the different temperature-dependent responses of Eu2+ and Eu3+. This work may give new ideas for the future research of optical thermometric materials with high sensitivity and high discriminability.
关键词： Fluorescence intensity ratio,Charge transfer band,Thermometry phosphor,LaAlO3
更新于2025-11-14 15:13:28
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A printed dual-band dipole filtenna with flexible frequency ratio and improved band-notched performance
摘要： A printed dual-band dipole filtenna with flexible frequency ratio and improved band-notched performance is proposed. It consists of a driven dipole and three parasitic elements. For the driven dipole with short and long arms, a radiation null is found between two passbands, which achieves a band-notched filtering characteristic. Two parasitic elements are introduced to enhance the passband bandwidth and an additional parasitic element is utilized to improve the band-notched performance. In addition, the characteristics of the proposed design including flexible frequency ratio, independent controllable operating frequency, and controllable band-notched bandwidth have also been demonstrated. A filtenna prototype is fabricated and tested. Measured results show that a fractional bandwidth of 21.1% and 18.1% is obtained in the lower and upper passbands, respectively. The measured efficiency is 84% in the lower band and 74% in the upper band but the efficiency sharply decreases to about 13% within the notched band.
关键词： filtenna,band-notched,dipole antenna,dual-band,frequency ratio
更新于2025-09-23 15:23:52
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Polarization independent quad-bandpass frequency selective surfaces with wide-band ratio
摘要： A single layer polarization independent quad-bandpass frequency selective surface (FSS) with wide-band ratio is demonstrated theoretically as well as experimentally. The proposed structure passes four frequency bands with wide band ratio. The proposed FSS design is implemented by incorporating alternate arrangement of four units which are rotated 90° clockwise to form a unit cell of metal over a FR4 substrate. The geometrical dimensions of proposed unit cell are optimized and arranged in such a way that the structure possesses the quad bandpass characteristic and aspect dimensions of one unit is 0.11λ × 0.11λ with respect to first resonant frequency. This FSS provides stable response for different angle of incidence in transverse electric (TE) mode and transverse magnetic (TM) mode. To validate the results proposed FSS array has been fabricated and measured in free space environment. The measured results are in good agreement with the simulated results. Excellent stability is also observed for different incident angle.
关键词： quad bandpass,polarization independent,frequency selective surface,band ratio
更新于2025-09-23 15:23:52