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Imaging multiple Rydberg wave packets from shaper-generated two-color femtosecond pump-probe sequences
摘要： We combine a bichromatic white light polarization pulse shaping scheme with angle- and energy-resolved photoelectron spectroscopy to image the dynamics of atomic Rydberg wave packets. Background-free detection of the Rydberg dynamics is performed using shaper-generated bichromatic linearly and circularly polarized femtosecond pump-probe pulse sequences. Photoelectron momentum distributions from linearly polarized bichromatic fields feature pronounced time-, energy-, and angle-dependent dynamics, which result from the interference of s-, d-, and g-type photoelectron wave packets from the ionization of the Rydberg np and nf series. Detailed analysis of the highly differential data allows us to extract the dynamics of both Rydberg wave packets separately. The results are experimentally verified by additional pump-probe studies with bichromatic circularly polarized pulse sequences, which exclusively map the dynamics of the Rydberg nf series via g-type photoelectron wave packets.
关键词： Rydberg wave packets,pump-probe spectroscopy,photoelectron imaging,femtosecond lasers,polarization pulse shaping
更新于2025-09-23 15:23:52
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Current-induced domain wall oscillations in a nanowire imaged by time-resolved photoemission electron microscopy
摘要： We study reversible domain wall motion in half-ring Ni80Fe20 nanowires on a nanosecond (ns) timescale in a truly current-induced pump-probe experiment using an energy filtered, aberration-corrected photoemission electron microscope. The x-ray magnetic circular dichroism signal is probed at different time delays before, during and after the current pulse in a stroboscopic mode with circularly polarized synchrotron radiation in the energy range of the Fe L3-edge (707 eV). We observe lateral domain wall oscillations with a frequency of ～ 0.4 GHz. Comparing the results to a proposed string model, we find that the domain wall oscillations can be described as string-like asymmetric oscillations.
关键词： Synchrotron radiation,Photoemission electron microscopy,X-ray magnetic circular dichroism,Pump-probe mode
更新于2025-09-23 15:23:52
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Investigation of ultrafast energy transfer mechanism in BODIPY–Porphyrin dyad system
摘要： Novel β-fused BODIPY-Porphyrin compounds that contain free base porphyrin (TPP2BDP) and its Ni(II) complex (NiTPP2BDP) were synthesized to investigate intramolecular energy transfer mechanisms of β-fused BODIPY-porphyrin dyads and effect of the unfilled d shell metal ion on energy transfer mechanism. Fluorescence spectra of compounds exhibited that BODIPY emission was diminished upon excitation of the BODIPY unit because of the energy transfer from BODIPY to porphyrin unit. Femtosecond pump-probe spectroscopy measurements revealed that energy transfer of investigated compounds are faster than previous studies in literature. Rapid energy transfer (about 500 fs) from BODIPY to porphyrin was observed for both compounds when BODIPY unit is excited due to direct linkage of BODIPY to porphyrin unit. Intersystem crossing mechanism was also observed for the compound that contains free base porphyrin (TPP2BDP), whereas d-d transition was observed for the compound that contains metalloporphyrin (NiTPP2BDP) due to unfilled d orbital of Ni(II) ion.
关键词： Fast energy transfer,Borondipyrromethene,Porphyrin,Ultrafast pump-probe spectroscopy
更新于2025-09-23 15:23:52
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Contactless Optical Characterization of Carrier Dynamics in Free-Standing InAs-InAlAs Core-Shell Nanowires on Silicon
摘要： Contactless time-resolved pump-probe and external quantum efficiency measurements were performed on epitaxially grown free-standing wurtzite indium arsenide/indium aluminum arsenide (InAs-InAlAs) core-shell nanowires on Si (111) substrate from 77K to 293K. The first independent investigation of Shockley-Read-Hall, radiative and Auger recombination in InAs-based NWs is presented. Although the Shockley-Read Hall recombination coefficient was found to be at least two orders of magnitude larger than the average experimental values of other reported InAs materials, the Auger recombination coefficient was reported to be ten-fold smaller. The very low Auger and high radiative rates result in an estimated peak internal quantum efficiency of the core-shell nanowires as high as 22% at 77K, making these nanowires of potential interest for high efficiency mid-infrared emitters. A greater than two-fold enhancement in minority carrier lifetime was observed from capping nanowires with a thin InAlAs shell due to passivation of surface defects.
关键词： Auger recombination rate,radiative,Shockley-Read-Hall,Pump-probe spectroscopy,core-shell nanowires,surface/interface recombination velocity,minority carrier lifetime
更新于2025-09-23 15:23:52
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Ultrafast electron-lattice thermalization in copper and other noble metal nanoparticles
摘要： Using time-resolved ultrafast pump-probe spectroscopy we investigated the electron-lattice energy transfer in small copper nanospheres with diameters ranging from 3.2 to 23 nm, either embedded in a glass or dispersed in a solvent. Electron-lattice scattering rate is shown to increase with size reduction, in agreement with our previous results obtained on gold and silver nanoparticles in the low excitation regime. We attribute this effect to the reduction of the screening efficiency of electron–phonon interactions close to the nanoparticle surface. To understand the discrepancy between the results on the electron-lattice scattering in different metals reported in the literature (reduction, no dependence or increase with nanoparticle size), we discuss the experimental conditions required for the accurate determination of electron-lattice energy transfer time from time-resolved investigations in the weak and strong excitation regimes and present power-dependent experiments on gold nanospheres in solution. Our findings are derived from a theoretical analysis based on the two-temperature model predictions and on a complete modeling of the nanoparticle transient extinction cross-section through the resolution of Boltzmann equation in the presence of hot electrons.
关键词： pump-probe spectroscopy,copper nanoparticles,electron-lattice interactions,two-temperature model,ultrafast electron dynamics
更新于2025-09-23 15:23:52
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Carrier-Induced Coherent Phonon Softening in Bismuth
摘要： With performing time-resolved pump-probe experiments with ultrashort pulses from a mode-locked Ti:sapphire laser, we report on the carrier-induced softening and dephasing of coherent phonon oscillations in the bismuth crystal. As the lattice displacement becomes severe at high pump power, a frequency shift can occur due to the lattice anharmonicity term. We clari?ed from the measurements done by varying the pulse duration that the phonon softening at high pump intensity in bismuth originates from the electron-interaction of photoexcited carriers not from the phonon anharmonicity. We also ?nd that the coherent phonon dephasing is accelerated at high carrier densities.
关键词： Pump-probe,Coherent phonon,Phonon softening
更新于2025-09-23 15:22:29
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Enhancement of attosecond pulse in water window region by using pump-probe approach
摘要： An effective scheme to enhance the harmonic yield and the attosecond (as) pulse signal from H+2 has been proposed by using the pump-probe laser field. It is found that with the help of the multi-cycle pump pulse, H+2 can be steered into the resonance ionization regions, where the ionization probability can be remarkably enhanced. Thus, the harmonic yield can be remarkably enhanced when a sequential mid-infrared probe pulse is added. Further, by modulating the phase of the probe pulse and by adding a controlling pulse, the harmonic cutoff can be extended up to the water window region. Finally, by the Fourier transformation of the selected harmonics on the harmonic supercontinuum, the water window attosecond pulses as short as 25 as can be obtained.
关键词： High-order harmonic generation,pump-probe pulse,charge resonance enhanced ionization,single attosecond pulse,harmonic enhancement
更新于2025-09-23 15:21:21
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Hot electron thermoreflectance coefficient of gold during electron-phonon nonequilibrium
摘要： The temperature-dependent reflectivity of metals is quantified by the thermoreflectance coefficient, which is a material dependent parameter that depends on the metallic band structure, electron scattering dynamics, and photon wavelength. After short-pulse laser heating, the electronic sub-system in a metal can be driven to temperatures much higher than that of the lattice, which gives rise to unique non-equilibrium electron and phonon scattering dynamics, leading to a “hot electron” thermoreflectance that is different from the traditionally measured equilibrium coefficient. In this work, we analytically quantify and experimentally measure this hot electron thermoreflectance coefficient through ultrafast pump-probe measurements of thin gold films on silica glass and sapphire substrates. We demonstrate the ability to not only quantify the thermoreflectance during electron-phonon nonequilibrium, but also validate this coefficient’s predicted dependence on the absolute temperature of the electronic subsystem. The approach outlined in this work provides a metrology to further understand and quantify excited-state scattering effects on the dielectric function of metals.
关键词： electron-phonon scattering,Pump-probe,Thermoreflectance,Drude model,electronic temperature
更新于2025-09-23 15:21:21
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Vibrational fingerprint of localized excitons in a two-dimensional metal-organic crystal
摘要： Long-lived excitons formed upon visible light absorption play an essential role in photovoltaics, photocatalysis, and even in high-density information storage. Here, we describe a self-assembled two-dimensional metal-organic crystal, composed of graphene-supported macrocycles, each hosting a single FeN4 center, where a single carbon monoxide molecule can adsorb. In this heme-like biomimetic model system, excitons are generated by visible laser light upon a spin transition associated with the layer 2D crystallinity, and are simultaneously detected via the carbon monoxide ligand stretching mode at room temperature and near-ambient pressure. The proposed mechanism is supported by the results of infrared and time-resolved pump-probe spectroscopies, and by ab initio theoretical methods, opening a path towards the handling of exciton dynamics on 2D biomimetic crystals.
关键词： FeN4 center,spin transition,ab initio theoretical methods,excitons,carbon monoxide,infrared spectroscopy,graphene,time-resolved pump-probe spectroscopy,two-dimensional metal-organic crystal
更新于2025-09-23 15:21:21
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Influence of magnetic field orientation on laser-induced magnetization precession in Ni-Mn-Sn Heusler alloy film
摘要： Laser-induced magnetization precession is investigated in Ni-Mn-Sn Heulser alloy film using pump-probe all-optical technique. The studies are performed as a function of external magnetic field H applied at various angles with respect to the sample normal. Strong dependence of precession parameters, frequency f, amplitude A and effective damping, two precession modes, identified as Damon-Eshbach (DE) and first-order standing spin wave (PSSW) modes were observed. The values of wave vector for DE mode have been determined. The experimentally obtained exponentially decayed. The dependencies of the magnetization precession parameters have been well simulated in the frame of phenomenological approach, based on Landau-Lifshitz-Gilbert equation.
关键词： standing spin wave mode,pump-probe all-optical technique,Landau-Lifshitz-Gilbert equation,Ni-Mn-Sn Heusler alloy,Damon-Eshbach mode,Laser-induced magnetization precession
更新于2025-09-23 15:21:01