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- PIN diode
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- Ufa State Aviation Technical University
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Multi-channel averaging detection for fast imaging of weakly absorbing defects in surface thermal lensing
摘要： Surface thermal lensing (STL) is a high sensitive pump-probe technique for photothermal characterization of weakly absorbing defects in optical materials. Commonly, the frequency modulation is applied in the pump beam, and the STL signal that appears as small modulation on top of an intense background is then detected on the probe beam by lock-in amplification. However, the lock-in detection by filtering the signal in the frequency domain results in low efficiency in the STL, preventing investigations of the large area surfaces. Here it is shown that the multi-channel averaging, which corresponds to temporal integration, is better suited for detection of the STL signal. It is demonstrated that by converting the conventional single-point scanning STL to the line scanning STL and employing suitable width of the time bins and the number of records, the imaging speed of the multi-channel averaging detection can be improved by a factor of 3.7 relative to the lock-in detection at the same signal-to-noise ratio of 6 dB and imaging resolution of 20 μm. Therefore, high-quality photothermal images of weakly absorbing defects can be recorded with higher efficiency and lower laser irradiance, making it possible to investigate large samples.
关键词： photothermal characterization,weakly absorbing defects,multi-channel averaging,Surface thermal lensing,optical materials
更新于2025-09-04 15:30:14
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Effect of N <sub/>2</sub> /H <sub/>2</sub> plasma on GaN substrate cleaning for homoepitaxial GaN growth by radical-enhanced metalorganic chemical vapor deposition (REMOCVD)
摘要： We developed a new method of GaN growth using Radical-Enhanced Metalorganic Chemical Vapor Deposition (REMOCVD) technology by which Gallium Nitride (GaN) grows at low temperatures without ammonia gas. In this method, we investigated the effect of N2/H2 plasma on the GaN substrate surface cleaning prior to the growth of homoepitaxial GaN. In-situ reflection high-energy electron diffraction (RHEED) and atomic force microscope (AFM) were used to investigate the surface morphology of the cleaned GaN substrates. The interface between GaN substrate and homoepitaxially grown GaN by REMOCVD was evaluated by transmission electron microscope and the crystal quality was evaluated by X-ray diffraction. The in-situ N2/H2 plasma cleaning at 600 ?C shows a smooth surface morphology with streak diffraction lines observed by RHEED. Since the homoepitaxial growth of GaN was performed at 800 ?C, the cleaned GaN substrate temperature was ramped up from 600 ?C to 800 ?C with and without plasma exposure to compare the effect of plasma. Homoepitaxially grown GaN on GaN substrates whose temperature was ramped up with plasma exposure showed good crystal quality with no threading dislocations at the interface. It was found that N2/H2 plasma plays a significant role in the GaN surface cleaning for good quality crystal growth.
关键词： surface cleaning,homoepitaxial growth,N2/H2 plasma,GaN,REMOCVD
更新于2025-09-04 15:30:14
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Surface Plasmon Resonance in a metallic nanoparticle embedded in a semiconductor matrix: exciton-plasmon coupling
摘要： We consider the effect of electromagnetic coupling between localized surface plasmons in a metallic nanoparticle (NP) and excitons or weakly interacting electron-hole pairs in a semiconductor matrix where the NP is embedded. An expression is derived for the NP polarizability renormalized by this coupling and two possible situations are analyzed, both compatable with the conditions for Fano-type resonances: (i) a narrow bound exciton transition overlapping with the NP surface plasmon resonance (SPR), and (ii) SPR overlapping with a parabolic absorption band due to electron-hole transitions in the semiconductor. The absorption band lineshape is strongly non-Lorentzian in both cases and similar to the typical Fano spectrum in the case (i). However, it looks differently in the situation (ii) that takes place for gold NPs embedded in a CuO film and the use of the renormalized polarizability derived in this work permits to obtain a very good fit to the experimentally measured LSPR lineshape.
关键词： Localized surface plasmon,Nanoparticle,Semiconductor,Dielectric function,Composite,Fano resonance,Exciton
更新于2025-09-04 15:30:14
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Symmetric surface complex waves in Goubau Line
摘要： Existence of symmetric surface complex waves in a Goubau line—a perfectly conducting cylinder of circular cross-section covered by a concentric dielectric layer—is proved by constructing perturbation of the spectrum of symmetric real waves with respect to the imaginary part of the permittivity of the dielectric cover. Closed-form iteration procedures for calculating the roots of the dispersion equation (DE) in the complex domain supplied with efficient choice of initial approximation are developed. Numerical modeling is performed with the help of a parameter-differentiation method applied to the analytical and numerical solution of DEs.
关键词： dispersion equation,attenuation,losses,Goubau line,complex surface wave
更新于2025-09-04 15:30:14
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Mapping of mangrove coverage and canopy height using LiDAR data at Sangkulirang District, East Kutai, East Borneo
摘要： Light Detection and Ranging (LiDAR) is remote sensing technology using transmitted properties of scattered light to detect the intended target. This technology potentially used for spatial planning and management, including mangrove monitoring. The purpose of this research was to map the mangrove coverage and canopy height using airborne LiDAR data at mangrove areas of Sangkulirang district, East Kutai, East Borneo. The corrected point cloud LiDAR data inputed into 10 blocks boundary. This data is classified into 7 classes (ground, mangroves, non mangroves, water, vehicle, low point and isolated point). Ground class used as the data source for digital terrain model (DTM) while mangrove class used as the data source for digital surface model (DSM). The substraction from overlaying DTM - DSM will produce canopy height model (CHM) that represent the height of mangroves canopy from land. The result of this research showed that mangrove distribution had an area of 64.07 km2. The height of mangrove canopy was dominated by 10-30 meters height while the maximum height reached 54.04 meters.
关键词： canopy height,mangrove,digital terrain model,digital surface model,LiDAR
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Design of Millimetre Wave Phase Shifting Periodic Metasurfaces
摘要： A high impedance surface capable of analogue phase shifting in the millimetre wave band has been simulated and is realisable with the use of piezoelectric actuators with enhanced displacement. The phase shifter demonstrates a signi?cantly higher bandwidth and frequency range, along with lower losses, than previously proposed systems. Tuning can be achieved with a single, mechanically ampli?ed, piezoelectric actuator. Using the available displacement provided by such actuators, it has been demonstrated that over 200 degrees of phase shift should be achievable over a 27 GHz band when utilising the improved patch unit cell.
关键词： phase shifter,high impedance surface,millimetre wave
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Hangzhou, China (2018.8.13-2018.8.17)] 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Sensing Characteristics of Fano Resonance in Y-shaped Gold Nanorods Array
摘要： Fano resonance of metallic nanostructure is good for reducing the irradiation loss. Fano resonance of metallic nanostructure is also could improve the spectral resolution. Due to its unique sensitivity, Fano resonance is widely used in physics and engineering fields such as optical sensors, optical switches transparent resonators. In this paper, time-domain finite difference method is used to design a kind of Y-type gold periodic nanorods array, which has obvious Fano resonance phenomenon at 1.12-(cid:541)m wavelength. When the array structural parameters change, the Fano resonance valley has a dramatic movement. The Y-type gold nanoarray structures have better sensing characteristics, and its figure of merit is 10.68. It shows the special nanoarray can be used for infrared sensors.
关键词： finite difference time domain,Fano resonance,localized surface plasmon resonance
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - 140 GHz Linear to Circular Polarization Convertor Based on Modified Cross Slot Frequency Selective Surface with High Selectivity
摘要： A 140 GHz linear to circular polarization converter based on a frequency selective surface (FSS) with high selectivity is proposed and designed in this paper. The periodic element of the converter includes a square substrate integrated waveguide (SIW) cavity and two cross slots with stubs etched on the top and bottom conductor claddings of the cavity. Based on the SIW cavity, a transmission pole is provided to improve passband characteristics and sideband selectivity. Besides, this THz converter can be easily fabricated using normal PCB process instead of compacted and high-cost technologies.
关键词： high selectivity,frequency selective surface (FSS),circular polarization (CP),Terahertz (THz) technology,substrate integrated waveguide (SIW) cavity
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - High Sensitivity Inkjet-Printed Terahertz Metallic Hole Array Sensor
摘要： Surface plasmon resonance sensors based on the resonant transmission characteristics of metal hole arrays are fabricated using conductive inkjet printing for operation in the terahertz region. The response of the sensing surfaces is measured using terahertz time domain spectroscopy. The addition of a layer of glycerol on the surface that is much thinner than the wavelength of the incident wave is simulated and results in a significant shift of the resonance frequency. This indicates the possibility of realising a flexible low-cost sensor for chemical and biological substances.
关键词： metamaterial,surface plasmon polariton,inkjet,sensor,Conductive ink printing
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Microwave Absorber Using Single-layer FSS with Wideband Operation Above the X-band
摘要： This work presents the design of a planar microwave absorber based on frequency selective surface (FSS). The absorber provides wide absorption bandwidth above the X-band. The proposed design consists of a single-layer FSS over a ground plane. The unit cell of the FSS is a miniaturized form of a rectangular loop structure made of perfect electric conductor (PEC). For absorption, lumped resistive elements are inserted on the four sides of the loop. The designed is modeled and analyzed using a commercial full-wave package and the absorption mechanism is explained by an equivalent circuit. Through simulations, the absorption bandwidth obtained for the proposed design is between 14.2-30.3 GHz. The angular stability of the proposed design is also analyzed and it is found be stable for 45o and 30o in TE and TM modes, respectively.
关键词： lumped resistors,microwave absorber,wideband,frequency selective surface(FSS)
更新于2025-09-04 15:30:14