- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Gate switching of ultrafast photoluminescence in graphene
摘要： The control of optical properties by electric means is the key to optoelectronic applications. For atomically thin two-dimensional (2D) materials, the natural advantage lies in that the carrier doping could be readily controlled through the electric gating effect, possibly affecting the optical properties. Exploiting this advantage, here we report the gate switching of the ultrafast upconverted photoluminescence from monolayer graphene. The luminescence can be completely switched off by the Pauli-blocking of one-photon interband transition in graphene, with an on/off ratio exceeding 100 times, which is remarkable compared to other 2D semiconductors and 3D bulk counterparts. The chemical potential and pump fluence dependences of the luminescence are nicely described by a two-temperature model, including both the hot carrier dynamics and carrier-optical phonon interaction. This gate switchable and background-free photoluminescence can open up new opportunities for graphene-based ultrafast optoelectronic applications.
关键词： ultrafast photoluminescence,gate switching,hot carriers,graphene,optoelectronics,two-temperature model
更新于2025-09-09 09:28:46
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High-harmonic generation from solids
摘要： High-harmonic generation in atomic gases has been studied for decades, and has formed the basis of attosecond science. Observation of high-order harmonics from bulk crystals was, however, reported much more recently, in 2010. This Review surveys the subsequent efforts aimed at understanding the microscopic mechanism of solid-state harmonics in terms of what it can tell us about the electronic structure of the source materials, how it can be used to probe driven ultrafast dynamics and its prospects for novel, compact short-wavelength light sources. Although most of this work has focused on bulk materials as the source, recent experiments have investigated high-harmonic generation from engineered structures, which could form flexible platforms for attosecond photonics.
关键词： ultrafast dynamics,electronic structure,high-harmonic generation,solids,short-wavelength light sources,attosecond science
更新于2025-09-09 09:28:46
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Transient Glass Formation around a Quadrupolar Photoexcited Dye in a Strongly H-Bonding Liquid Observed by Transient 2D-IR Spectroscopy
摘要： A photoexcited quadrupolar dye is directly observed using transient 2D-IR spectroscopy. Upon solvent-induced symmetry breaking, the H-bond accepting abilities of the two nitrile end-groups change drastically, and in extreme protic (‘superprotic’) solvents, a tight H-bond complex forms at one end. The time evolution of the 2D C≡N lineshape in methanol points to rapid, 2-3 ps, spectral diffusion due to fluctuations of the H-bonding network. Similar behaviour is observed in a superprotic solvent shortly after photoexcitation of the dye. However, at later time, the completely inhomogeneous band does not exhibit spectral diffusion for at least 5 ps, pointing to a glass-like environment around one side of the dye. About half of the excited dyes show this behaviour attributed to the tight H-bond complex, whereas the others are loosely bound. A weak cross peak these excited state sub- indicates partial exchange between populations.
关键词： charge transfer,symmetry breaking,ultrafast spectroscopy,Hydrogen bonds,solvation dynamics
更新于2025-09-09 09:28:46
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Vortex Dynamics and Optical Vortices || Ultrashort Extreme Ultraviolet Vortices
摘要： Optical vortices are very attractive because they transport a well-defined orbital angular momentum (OAM) associated with the singularity of the beam. These singular beams, commonly generated in the optical regime, are used in a wide range of applications: communication, micromanipulation, microscopy, among others. The production of OAM beams in the extreme ultraviolet (XUV) and X-ray regimes is of great interest as it allows to extend the applications of optical vortices down to the nanometric scale. Several proposals have been explored in order to generate XUV vortices in synchrotrons and FEL facilities. Here, we study the generation of XUV vortices through high-order harmonic generation (HHG). HHG is a unique source of coherent radiation extending from the XUV to the soft X-ray regime, emitted in the form of attosecond pulses. When driving HHG by OAM beams, highly charged XUV vortices with unprecedented spatiotemporal properties are emitted in the form of helical attosecond beams. In this chapter, we revise our theoretical work in the generation of XUV vortices by HHG. In particular, we illustrate in detail the role of macroscopic phase matching of high-order harmonics when driven by OAM beams, which allows to control the production of attosecond beams carrying OAM.
关键词： attosecond helical beams,ultrafast phenomena,orbital angular momentum,attosecond pulses,extreme ultraviolet vortices,high harmonic generation,nonlinear optics,phase matching
更新于2025-09-09 09:28:46
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Single-shot Real-time Sub-nanosecond Electron Imaging Aided by Compressed Sensing: Analytical Modeling and Simulation
摘要： Bringing ultrafast (nanosecond and below) temporal resolution to transmission electron microscopy (TEM) has historically been challenging. Despite significant recent progress in this direction, it remains difficult to achieve sub-nanosecond temporal resolution with a single electron pulse, in real-time (i.e., duration in which the event occurs) imaging. To address this limitation, here, we propose a methodology that combines laser-assisted TEM with computational imaging methodologies based on compressed sensing (CS). In this technique, a two-dimensional (2D) transient event [i.e. (??, ??) frames that vary in time] is recorded through a CS paradigm, which consists of spatial encoding, temporal shearing via streaking, and spatiotemporal integration of an electron pulse. The 2D image generated on a camera is used to reconstruct the datacube of the ultrafast event, with two spatial and one temporal dimensions, via a CS-based image reconstruction algorithm. Using numerical simulation, we find that the reconstructed results are in good agreement with the ground truth, which demonstrates the applicability of CS-based computational imaging methodologies to laser-assisted TEM. Our proposed method, complementing the existing ultrafast stroboscopic and nanosecond single-shot techniques, opens up the possibility for single-shot, real-time, spatiotemporal imaging of irreversible structural phenomena with sub-nanosecond temporal resolution.
关键词： ultrafast imaging,compressed sensing,streak imaging,transmission electron microscopy
更新于2025-09-09 09:28:46
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[IEEE 2017 International Conference on Optical Network Design and Modeling (ONDM) - Budapest (2017.5.15-2017.5.18)] 2017 International Conference on Optical Network Design and Modeling (ONDM) - Ultrafast InGaAs photoswitch for RF signal processing
摘要： Optical processing of radiofrequency signals is demonstrated in this communication using photoswitches made from nitrogen ion implanted InGaAs. The sampling device shows an ultrafast picosecond response time while activated by ultra-short optical pulses or modulated optical beam centered at the wavelength of 1.55 μm. The optoelectronic device is embedded in a microwave coplanar waveguide which has a high electrical bandwidth allowing to process signals in the 1-67 GHz band. We investigate the potentiality of this component to be used either in photonic assisted sampling for future analog-to-digital converters or in photonic assisted heterodyne detection of RF modulated carriers.
关键词： ion implanted InGaAs,photonic assisted data processing,radio over fiber,ultrafast electronics,Photoconductive sampling,heterodyne photomixer,metal-semiconductor-metal devices
更新于2025-09-09 09:28:46
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Bright and Ultrafast Photoelectron Emission from Aligned Single-Wall Carbon Nanotubes through Multiphoton Exciton Resonance
摘要： Ultrashort bunches of electrons, emitted from solid surfaces through excitation by ultrashort laser pulses, are an essential ingredient in advanced X-ray sources and ultrafast electron diffraction spectroscopy. Multiphoton photoemission using a noble metal as the photocathode material is typically used, but more brightness is desired. Artificially structured metal photocathodes have been shown to enhance optical absorption via surface plasmon resonance, but such an approach severely reduces the damage threshold in addition to requiring state-of-the-art facilities for photocathode fabrication. Here, we report ultrafast photoelectron emission from sidewalls of aligned single-wall carbon nanotubes. We utilized strong exciton resonances, inherent in this prototypical one-dimensional material, as well as the high damage threshold owing to their excellent thermal conductivity and mechanical rigidity. We obtained unambiguous evidence for resonance-enhanced multiphoton photoemission processes with definite power-law behaviors. In addition, we observed strong polarization dependence and ultrashort photoelectron response time, both of which can be quantitatively explained by our model. These results firmly establish aligned single-wall carbon nanotube films as a novel and promising ultrafast photocathode material.
关键词： depolarization effect,ultrafast,multiphoton,photoemission,carbon nanotubes,photocathode
更新于2025-09-09 09:28:46
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Ultrafast optical control of multiple coherent phonons in silicon carbide using a pulse-shaping technique
摘要： We demonstrated ultrafast optical control of multiple coherent phonons in silicon carbide (SiC) using a pulse-shaping technique combined with sub-10-fs optical pulses and a two-dimensional spatial light modulator. Because our technique produces a pulse train with the desired number of pulses and time intervals, precise manipulation of the amplitudes of the zone-folded optical and acoustic phonon modes could be achieved simultaneously and was well reproduced by a model calculation assuming the two modes are excited independently by each pulse. These results show that our scheme can provide high controllability of multiple phonon modes in SiC.
关键词： pulse-shaping technique,coherent phonons,ultrafast optical control,silicon carbide
更新于2025-09-09 09:28:46
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Characterization of ultrafast plasmon dynamics in individual gold bowtie by time-resolved photoemission electron microscopy
摘要： We report on the investigation of ultrafast dynamics of the plasmonic field in individual gold bowtie nanostructure by combining interferometric time-resolved photoemission electron microscopy with a damped harmonic oscillator model. We experimentally obtain different plasmon dephasing times in the tips of the bowtie nanostructure. In the meantime, we demonstrate that the experimental time-resolved photoemission signal can be used to directly compare resonance frequency and dephasing time of different hot spots. In addition, we find that the plasmon field, which is extracted from the photoemission signal, initially oscillates at the laser field frequency, and finally develops into its eigenfrequency after experiencing a few periods of frequency fluctuation due to the competition between forced and autonomous oscillation of the plasmons.
关键词： ultrafast plasmon dynamics,gold bowtie,resonance frequency,plasmon dephasing times,time-resolved photoemission electron microscopy
更新于2025-09-09 09:28:46
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Probing the upper band gap of atomic rhenium disulfide layers
摘要： Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13 nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57 eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden d–d intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38 eV) with wavelength-variant SHG probes (2.60–2.82 eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05 eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5 eV) using modified DFT calculations.
关键词： density functional theory,ReS2,time-resolved spectroscopy,ultrafast carrier dynamics,second harmonic generation
更新于2025-09-09 09:28:46