- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Stark shift in Y <sub/>2</sub> SiO <sub/>5</sub> :Er <sup>3+</sup> by the photon echo beating method
摘要： The coefficient of a linear Stark shift of the 4F9/2–4I15/2 transition of Er3+ ion in Y2SiO5 is measured (14.3 kHz V?1 cm ) by splitting the upper and lower levels of the transition by a pulsed electric field and measuring the splitting frequency from the period of beatings of the temporal form of a photon echo signal (stark photon echo beating method). The linear Stark coefficients of Er3+ transitions in Y2SiO5 have not been measured before, and this is a valuable result for a number of applications such as gradient echo memory, group velocity control via spectral hole burning, etc.
关键词： Er3+,phase control,Stark coefficient,Stark photon echo beating,Y2SiO5,YSO,low electric field pulse
更新于2025-09-23 15:23:52
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Combination of OPSY and PhD-PHIP results in enhanced sensitivity in PHIP
摘要： Despite the large degree of polarization in PHIP experiments compared to the Boltzmann factor, the presence of a large amount of non-reacted molecules with thermal polarization is an important obstacle when dealing with very diluted samples. The feasibility of enhancing both sensitivity and resolution in a single experiment by combining two well established pulse sequences, OPSY and PHD-PHIP is presented. OPSY is used as a block for filtering the signals originated from thermally polarized protons. PhD-PHIP, on the other hand, is used as an acquisition block, increasing the resolution and further improving the sensitivity by preventing signal canceling in the presence of magnetic field inhomogeneities. Experiments in a complex sample with very low hyperpolarization levels are presented showing the excellent performance of the method.
关键词： Echo trains,PhD-PHIP,Spin dynamics,CPMG,J-spectroscopy,Hyperpolarization,Pulse sequences,Parahydrogen,SABRE,J-coupling,NMR,OPSY,PHIP
更新于2025-09-23 15:23:52
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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) - Accurate Determination of Radiation Patterns from Near-Field Measurements in Highly Reflective Environments
摘要： The radiation pattern of an antenna under test is determined from measurements in a highly reflective, fully metallic measurement environment similar to a reverberation chamber. The undesired influence of the reflecting walls is eliminated by processing the data obtained for a large number of frequencies and different probe locations in the chamber. The post-processing concept effectively combines temporal and spatial filtering of the measured signals in an innovative field synthesis concept. S-Band measurements show the effectiveness of the proposed processing concepts. The accuracy is comparable to anechoic measurements, however, for the cost of increased measurement and post-processing effort.
关键词： echo suppression,near-field far-field transformation,antenna measurement
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on RFID Technology & Application (RFID-TA) - Macau, Macao (2018.9.26-2018.9.28)] 2018 IEEE International Conference on RFID Technology & Application (RFID-TA) - Research on Fast Algorithm for General Bistatic SAR Raw Signal
摘要： A fast algorithm for general bistatic synthetic aperture radar (SAR) raw signal based on two-dimensional frequency domain is proposed. The SAR echo signal model is established by the algorithm, the accurate expression of two-dimensional frequency domain for the bistatic SAR echo signal are deduced with series reversion. Simulating large range and azimuth coupling, the accurate computation of echo signal is realized and the complexity of the algorithm is analyzed. The simulation results show that the simulation speed of SAR echo is greatly improved under the premise of ensuring the high phase accuracy, and the validity of the algorithm is proved.
关键词： synthetic aperture radar (SAR),bistatic,series reversion,echo simulation
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - First in-Situ Demonstration of Passive Radio Sounding Using the Sun as a Source for Echo Detection
摘要： While radio echo sounders are powerful tools used to constrain subglacial conditions, current ice-penetrating radar systems are too resource intensive for multiyear deployment at a large scale. To address this, we present passive radio sounding as a low resource approach for observing the subsurface of ice sheets and glaciers. Although passive radar has been used for target tracking and military purposes, it has never been implemented for ice sounding. Nevertheless, recent work has proposed the passive radio sounding of Europa’s icy shell using Jupiter’s decametric radiation as a source for echo detection [1,2]. Expanding on this idea, we evaluate and discuss the challenges of developing a passive radio sounder that uses the Sun for echo detection. Our prototype measures the Sun’s direct and reflected path off the ocean to obtain the height of a cliff along the California coast. This serves as the first in-situ demonstration of an autocorrelation-based passive-sounder using a compact astronomical white noise source.
关键词： ice-penetrating radar,passive radar,radio echo sounding
更新于2025-09-23 15:22:29
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B-scan wave outline analysis in numerical modeling of ground-penetrating radar response from layered rough interfaces
摘要： Imaging of rough interfaces in a layered structure requires full understanding of the characteristics of their ground penetrating radar (GPR) echoes. In this study, a finite-difference time-domain computational model using a uniaxial perfectly matched layer boundary for GPR demining of layered rough interfaces is constructed. On the basis of this model, the numerical results of B-scan echoes from two-layered and three-layered rough interfaces with different degrees of roughness are obtained and compared with the profiles of corresponding rough surfaces. These results and comparisons highlight the relationship between the B-scan wave outlines and the profile of the layered rough interfaces. The effect of roughness of the interface on the B-scan echoes are analyzed, and the influence of the upper rough surface profile on the shape of the B-scan wave outline from the lower rough surface is discussed.
关键词： layered rough interfaces demining,finite-difference time-domain method (FDTD),ground penetrating radar (GPR),echo characteristic analysis
更新于2025-09-23 15:22:29
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Long Exciton Dephasing Time and Coherent Phonon Coupling in CsPbBr <sub/>2</sub> Cl Perovskite Nanocrystals
摘要： Fully-inorganic cesium lead halide perovskite nanocrystals (NCs) have shown to exhibit outstanding optical properties such as wide spectral tunability, high quantum yield, high oscillator strength as well as blinking-free single photon emission and low spectral diffusion. Here, we report measurements of the coherent and incoherent exciton dynamics on the 100 fs to 10 ns timescale, determining dephasing and density decay rates in these NCs. The experiments are performed on CsPbBr2Cl NCs using transient resonant three-pulse four-wave mixing (FWM) in heterodyne detection at temperatures ranging from 5 K to 50 K. We found a low-temperature exciton dephasing time of 24.5±1.0 ps, inferred from the decay of the photon-echo amplitude at 5 K, corresponding to a homogeneous linewidth (FWHM) of 54±5 μeV. Furthermore, oscillations in the photon-echo signal on a picosecond timescale are observed and attributed to coherent coupling of the exciton to a quantized phonon mode with 3.45 meV energy.
关键词： quantum dots,coherence,four wave mixing,nanocrystals,heterodyne detection,Perovskite,T2,lead halide,photon echo,phonons
更新于2025-09-23 15:21:21
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Kinetics of two-pulsed photon echo formed on the 0–1 transition: isotropic and anisotropic collisions
摘要： The photon echo formed at the intercombination (6s2) 1S0 ? (6s6p) 3P1 (type 0–1) transition of ytterbium atoms 174Yb by two pulses of resonance radiation was investigated as a function of the time delay between exciting pulses (the photon echo kinetics). For exciting radiation pulses of the same linear polarization in the delay region 70–250 ns, the photon echo kinetics is close to the exponential one both in pure ytterbium and in its mixtures with buffer gases Ar and Xe. The relaxation cross sections were determined for all three cases, taking into account the isotopic composition of xenon and ytterbium. For the first time, the complex nonmonotonous kinetics of the collision-induced photon echo was observed in the same mixtures for the forming pulses of linear mutually orthogonal polarization. The relative efficiency of buffer atoms Yb (other isotopes than 174Yb), Xe and Ar in the collision-induced photon echo formation was obtained.
关键词： collision induced photon echo,collision anisotropy,photon echo
更新于2025-09-23 15:21:01
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Geminate recombination in organic photovoltaic blend PCDTBT/PC <sub/>71</sub> BM studied by out-of-phase electron spin echo spectroscopy
摘要： The key process in organic solar cell operation is charge separation under light illumination. Due to the low dielectric constant of organic materials, the Coulomb attraction energy within the interfacial charge-transfer state (CTS) is larger than the thermal energy. Understanding the mechanism of charge separation at the organic donor/acceptor interface still remains a challenge and requires knowledge of the CTS temporal evolution. To address this problem, the CTS in the benchmark photovoltaic blend PCDTBT/PC71BM was studied by the out-of-phase Electron Spin Echo (ESE). The protocol for determining the CTS geminate recombination rate for certain electron-hole distances was developed. Simulating the out-of-phase ESE trace for the CTS in the PCDTBT/PC71BM blend allows precise determination of the electron-hole distance distribution function and its evolution with the increase in the delay after the laser flash. Distances of charge separation up to 6 nm were detected upon thermalization at a temperature of 20 K. Assuming the exponential decay of the recombination rate, the attenuation factor β = 0.08 ??1 is estimated for the PCDTBT/PC71BM blend. Such a low attenuation factor is probably caused by a high degree of hole delocalization along the PCDTBT chain.
关键词： PCDTBT/PC71BM blend,electron spin echo,geminate recombination,organic solar cells,charge transfer state
更新于2025-09-23 15:19:57
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Combined photon-echo, luminescence and Raman spectroscopies of layered ensembles of colloidal quantum dots
摘要： Low-temperature dynamics in layered ensembles of core-double-shell colloidal CdSe/CdS/ZnS quantum dots is studied using different experimental techniques, including photoluminescence and absorption spectroscopy, luminescence microscopy, photon echo, transmission electronic microscopy and Raman scattering. A combination of different techniques clarify the nature and hierarchy of relaxation processes in the quantum dot (QD)-composite under study for a broad range of temperatures and timescales. The parameters of local phonons in QDs was found coincident by luminescence and Raman spectroscopies. Different contributions to optical spectra broadening has been recognized and attributed to certain properties of QDs: quantum size effect, electron-phonon coupling, spectral diffusion and natural excited state lifetime.
关键词： Raman spectroscopy,optical dephasing,photon echo,luminescence spectra,quantum dots (QDs),electronic microscopy,low temperatures
更新于2025-09-23 15:19:57