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- 2019
- FSO Communication System
- Subcarrier Intensity Modulation
- Atmospheric Turbulence
- Bit Error Rate
- Average Irradiance
- Optoelectronic Information Science and Engineering
- Galgotias College of Engineering and Technology
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Spatial carrier phase shifting method for the phase recovery from two interferograms with closed fringes
摘要： A procedure is developed to recover the phase from two interferograms with a non-constant phase shift between them. This method may find broad applications when environmental disturbances do not allow implementing traditional phase shifting techniques which normally require three or more images. A spatial carrier phase shifting method is implemented to analyze the two measured temporal phase shifted interferometric images. This approach is very fast, avoids the use of fringe normalization techniques, preserves good tolerance against small (λ/20) or non-constant phase shifts, background and modulation variations and noise as tested in real and simulated data.
关键词： spatial carrier,interferogram evaluation,phase shifting,Fringe analysis,phase recovery
更新于2025-09-23 15:23:52
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Low-temperature dark anneal as pre-treatment for LeTID in multicrystalline silicon
摘要： Light and elevated temperature induced degradation (LeTID) is currently a severe issue in crystalline silicon photovoltaics, which has led to numerous efforts to both understand the mechanism and to mitigate it. Here we show that a low-temperature dark anneal performed as the last step in typical solar cell processing influences greatly LeTID characteristics, both the strength of the degradation and the degradation kinetics. While a relatively short anneal in the temperature range of 200–240 °C can be detrimental to LeTID by doubling the degradation intensity, an optimized anneal at 300 °C shows the opposite trend providing an efficient means to eliminate LeTID. Furthermore, we show that the simulated recombination activity of metal precipitation and dissolution during the dark anneal correlates with the experiments, suggesting a possible explanation for the LeTID mechanism.
关键词： PERC,Precipitation,Multicrystalline silicon,Minority-carrier lifetime,LeTID,Copper in silicon
更新于2025-09-23 15:23:52
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Artifacts in Transient Absorption Measurements of Perovskite Films Induced by Transient Reflection from Morphological Microstructures
摘要： Organolead halide perovskites MAPbX3 (MA = CH3NH3+; X = Cl?, Br?, I?) have attracted broad tremendous interest in the past 10 years for applications in solar cells and light-emitting devices. In evaluating the quality of the perovskite materials, spectroscopic characterizations such as static and time-resolved absorption and photoluminescence measurements are essential to examine their photophysical properties. A recent report found that the correct measurement of static absorption spectra of MAPbX3 films is indeed difficult due to the strong light scattering caused by their poor surface coverage or complex microstructures. These morphological complexities seem to be inevitable in thin-film fabrication and should not only affect the steady-state spectroscopic measurements but also can significantly impact the time-resolved spectroscopic characterizations, whose results are crucial for understanding photoinduced carrier dynamics in the examined materials. Photoexcited states in semiconductor materials induce changes in the real and imaginary parts of the dielectric function. This leads to changes in absorption (imaginary part) and reflectivity (real part), which can be substantial for materials with significant values of refractive index such as lead halide perovskites. Transient absorption (TA) spectroscopy is a typical technique that has been broadly used to probe photoexcited state dynamics in perovskites and other semiconductor materials. In TA measurements, a pump laser pulse is used to excite the perovskite films, and the induced absorption changes (ΔA) are recorded as a function of both wavelength and time. With the transmitted light as the probe (Figure 1a), the TA signal (ΔA) is mainly decided by the ratio of the intensity of transmitted probe light with and without pump excitation (see eq S1 in the SI), assuming that the loss of transmitted probe light completely results from the sample absorption. On the basis of the same experimental setup, transient reflection (TR) measurements can also be carried out by using the reflected probe light as detection signal (Figure 1b). The TR signal (ΔR/R) can also be determined by the ratio of the intensity of reflected probe light with and without pump excitation (see eq S4 in the SI). Unlike the TA measurements that mainly probe the bulk property of samples, the TR signal mainly detects the photoinduced reflection variations due to the refractive index change at the sample surface. Therefore, the TR spectrum and kinetics can be significantly different from those of TA even in the same sample. For example, previous TA and TR measurements have found dramatically faster carrier recombination kinetics on the surface than in the bulk of MAPbX3 perovskite films or single crystals because of the presence of more surface defects. There is an abnormal case in the regular TA measurements particularly when performed on the films with large and heterogeneous microstructures (e.g., films with poor coverage, large grains, and pinholes) because the loss of transmitted probe light in their TA measurements likely results not only from the sample absorption but also from the reflection of the film surface or the boundary of microstructures in samples. In this case, the measured transient spectrum, though collected in the transmittance mode as in TA, can contain contributions from both TA and TR signals (see Figure 1c and eq S6 in the SI). This could lead to distorted TA spectra and thus inaccurate analysis of photoinduced kinetics. A solution-processed organic or inorganic halide perovskite thin film is a typical material whose morphological microstructures were found to have significant impact on device performance. Although the photoinduced carrier dynamics in perovskite films has been extensively studied using TA spectroscopy, the possible artifacts in TA results induced by TR signal originating from the photoinduced reflectivity variation of film surfaces and microstructures have been overlooked. Herein, in order to clarify the influence of TR signal in the regular TA measurements, we performed a careful transient spectroscopic analysis on a series of MAPbBr3 perovskite films with different microstructure morphology. Meanwhile, TR measurements on MAPbBr3 single crystals (SCs) were carried out for comparison. We confirmed that the TA spectra measured in MAPbBr3 perovskite films with large and heterogeneous microstructures do comprise non-negligible TR signals from the photoinduced reflection of microstructures, with the weight of contribution increased from ～20 to ～100% as the size of the microstructure increased from <200 nm to 1?2 μm. The presence of TR signal leads to an “artifact” feature in the TA spectra and faster observed kinetics owing to the faster surface carrier recombination, which will thus mislead the analysis of bulk carrier dynamics. We also provided a method to reduce the TR signal in actual TA measurements by adding solvent with its refractive index close to the samples, by which the TR distortion can be suppressed to some extent.
关键词： artifacts,transient reflection,transient absorption,carrier dynamics,perovskite films,microstructures
更新于2025-09-23 15:23:52
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High-order harmonic generation of pulses with multiple timescales: selection rules, carrier envelope phase and cutoff energy
摘要： High harmonic generation (HHG) is sensitive to the carrier envelope phase (CEP) of its driving laser field if it is a sufficiently short pulse (several-cycle pulse). Here we show that strong CEP effects can also be found in HHG from long duration multi-cycle pulses (up to 200 fs at 800 nm central wavelength). We find that HHG from multi-cycle pulses may be CEP dependent when the driving pulse exhibits two distinct timescales (multi-timescale pulse): (i) a short timescale associated with the average frequency, and (ii) a long timescale associated with the pulse’s temporal periodicity. The interplay of these timescales results in significant changes to both the cutoff frequency, and the appearance of symmetry allowed harmonics in the spectrum as function of CEP, similar to HHG from several-cycle pulses. We relate this effect to the multi-timescale intensity variations in the driving pulse, and construct an analytical condition to access the phenomenon. Lastly, we numerically demonstrate reconstruction of the CEP through HHG from long duration multi-timescale pulses. Our work may be useful in several areas of strong-field physics and attosecond science, for example, allowing spectroscopy of multi-timescale processes (e.g. HHG from vibrationally active media), and paving the way towards CEP characterisation using long pulses.
关键词： carrier-envelope phase,dynamical symmetry,High harmonic generation
更新于2025-09-23 15:23:52
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High efficient catalytic degradation of tetracycline and ibuprofen using visible light driven novel Cu/Bi2Ti2O7/rGO nanocomposite: Kinetics, intermediates and mechanism
摘要： The photoexcited charge carriers trapping was an effective way to generate a large number of active species like O2?? and ?OH radicals to oxidize pharmaceutical molecules. In ternary Cu/Bi2Ti2O7/rGO composite Cu nanoparticles and rGO sheets act as charge carrier trappers and the suppression of e--h+ pair recombination was confirmed by Photoluminescence analysis. The Cu/Bi2Ti2O7/rGO composite exhibited higher photocatalytic degradation efficiency for degradation of ibuprofen and tetracycline molecules under visible light irradiation within 90 min. Therefore, this research designates a promising strategy for higher photoexcited charge carrier trapping photocatalyst design for efficient degradation of pharmaceutical molecules.
关键词： Nanocomposite,Visible light-driven,Hydrothermal,Pharmaceutical contamination.,Charge carrier trappers
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on Electron Devices and Solid State Circuits (EDSSC) - Shenzhen (2018.6.6-2018.6.8)] 2018 IEEE International Conference on Electron Devices and Solid State Circuits (EDSSC) - Analysis of 1/f Noise for Organic TFTs Considering Mobility Power-Law Parameter
摘要： Based on carrier number fluctuation model, 1/f noise is analyzed for organic thin-film transistors (TFTs) at low drain voltage. The carrier mobility is gate-voltage-dependent, and is described by a power-law function. The mobility power-law parameter α determines the relationship between drain current noise power spectral density (PSD) SIDS and drain current IDS, and it is found that SIDS /I 2 DS when α = 1. It is different from the well-known rule for the MOSFETs with the constant carrier mobility: When SIDS /I 2 DS , Hooge’s mobility fluctuation model dominates the 1/f noise.
关键词： carrier mobility,Thin-film transistor (TFT),analytical model,low frequency noise
更新于2025-09-23 15:23:52
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Kink Suppression and High Reliability of Asymmetric Dual Channel Poly-Si Thin Film Transistors for High Voltage Bias Stress
摘要： Asymmetrically designed polycrystalline silicon (poly-Si) thin film transistors (TFT) were fabricated and investigated to suppress kink effect and to improve electrical reliability. Asymmetric dual channel length poly-Si TFT (ADCL) shows the best reduction of kink and leakage currents. Technology computer-aided design simulation proves that ADCL can induce properly high voltage at floating node of the TFT at high drain-source voltage (VDS), which can mitigate the impact ionization and the degradation of the transconductance of the TFT showing high reliability under the hot carrier stress.
关键词： kink,reliability,TFT,hot carrier stress,poly-Si
更新于2025-09-23 15:23:52
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Ethyl violet–bovine serum albumin fluorescent protein nanovessels target to lysosomes and mitochondria
摘要： Aim: Organelles are essential in maintaining homeostasis of mammalian cells. Monitoring the morphology and dynamics of organelles is of significance in cell state determination and disease diagnosis. Materials & methods: We describe here a new material called ethyl violet–bovine serum albumin fluorescent protein nanovessel (EV–BSA FPN). Upon heating, BSA was denatured to form higher polyhedral structures, which was prone to EV binding. These dye–protein hybrid materials were red fluorescence emissive upon excitation. Results: EV–BSA FPNs can be readily internalized by mammalian cells and dual localized in lysosomes and mitochondria. Besides, EV–BSA FPN can serve as carriers and efficiently deliver drug into cells. Conclusion: EV–BSA FPNs can be dual function fluorescent vessels for both dual-organelle imaging and drug delivery.
关键词： dual-organelle localization,fluorescent protein nanovessel,lysosomes and mitochondria imaging,ethyl violet,drug carrier
更新于2025-09-23 15:23:52
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Optical Energy Characteristics of the Optimal Module of a Solar Composite Parabolic-Cylindrical Plant
摘要： The module of parabolic-cylindrical composite mirror concentrating system (MCS) is created with an optimal aperture angle (U) and relevant optimal size of the focal spot provided by flat mirror elements with the optimal size.
关键词： mirror concentrating systems,heat receiver,focal plane,parabolic-cylindrical concentrator,flat facets,heat carrier
更新于2025-09-23 15:23:52
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Spectrally Resolved Ultrafast Exciton Transfer in Mixed Perovskite Quantum Wells
摘要： Solution-processed perovskite quantum wells have been used to fabricate increasingly efficient and stable optoelectronic devices. Little is known about the dynamics of photogenerated excitons in perovskite quantum wells within the first few hundred femtoseconds – a crucial timescale on which energy and charge transfer processes may compete. Here we use ultrafast transient absorption and two-dimensional electronic spectroscopy to clarify the movement of excitons and charges in reduced-dimensional perovskite solids. We report excitonic funneling from strongly to weakly confined perovskite quantum wells within 150 fs, facilitated by strong spectral overlap and orientational alignment among neighboring wells. This energy transfer happens on timescales orders of magnitude faster than charge transfer, which we find to occur instead over 10 - 100s of picoseconds. Simulations of both F?rster-type interwell exciton transfer and free carrier charge transfer are in agreement with these experimental findings, with theoretical exciton transfer calculated to occur in 100s of fs.
关键词： energy transfer,Carrier,metal halide perovskite,two-dimensional electronic spectroscopy,layered perovskite,dynamics
更新于2025-09-23 15:23:52