- 标题
- 摘要
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- 实验方案
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Stimulated resonant inelastic x-ray scattering with chirped, broadband pulses
摘要： We present an approach for initiating and tracing ultrafast electron dynamics in core-excited atoms, molecules, and solids. The approach is based on stimulated resonant inelastic x-ray scattering induced by a single, chirped, broadband XUV or x-ray pulse. A first interaction with this pulse prepares a core-excited state wave packet by resonant core-excitation. A second interaction with the pulse at a later time induces the transition to valence-excited states, which is associated with stimulated emission. The preparation of the core-excited wave packet and the transition from the core-excited states to the valence-excited states occur at distinct chirp-dependent times. As a consequence, the stimulated emission carries information about the time evolution of the core-excited state wave packet.
关键词： XUV pulses,x-ray pulses,core-excited states,ultrafast electron dynamics,chirped pulses,stimulated resonant inelastic x-ray scattering
更新于2025-09-19 17:15:36
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Sub-Femtosecond Stark Control of Molecular Photoexcitation With Near Single-Cycle Pulses
摘要： Electric fields can tailor molecular potential energy surfaces by interaction with the electronic state-dependent molecular dipole moment. Recent developments in optics have enabled the creation of ultra-short few-cycle optical pulses with precise control of the carrier envelope phase (CEP) that determines the offset of the maxima in the field and the pulse envelope. This opens news ways of controlling ultrafast molecular dynamics by exploiting the CEP. In this work, we show that the photoabsorption efficiency of oriented H2CSO (sulfine) can be controlled by tuning the CEP. We further show that this control emanates from a resonance condition related to Stark shifting of the electronic energy levels.
关键词： ultrafast photochemistry,Ab initio multiple spawning (AIMS),few-cycle pulse,Stark effect,excited state dynamics
更新于2025-09-19 17:15:36
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Controlling the Near-Field of Metasurfaces for Free-Electron Multi-Harmonic Hard X-Ray Generation
摘要： Metasurfaces are subwavelength spatial variations in geometry and material, and offer us an ingenious way of manipulating far-field radiation. Here, we show that their ability to manipulate the near-field is also an extremely powerful lever in controlling nanophotonic photon-electron interactions. The metasurface near-field contains high-order spatial harmonics that can be leveraged to generate substantial high harmonic components, whose properties are directly tunable through the metasurface geometry, the electron energy and the incidence angle of the input laser. By developing an analytical theory that produces results in excellent agreement with our ab initio simulations, we show how the design of metasurface-enhanced plasmons can be leveraged to produce intense and highly-directional multi-harmonic emission in the X-ray and the gamma-ray range. Furthermore, we show that the use of few-cycle laser pulses is instrumental in enhancing the intensity and bandwidth of the radiation output while avoiding damage to the metasurface. As an example, we present the design of a four-color X-ray source.
关键词： X-rays,sources,ultrafast optics,plasmonics,metasurface
更新于2025-09-19 17:15:36
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An open-source software ecosystem for the interactive exploration of ultrafast electron scattering data
摘要： This paper details a software ecosystem comprising three free and open-source Python packages for processing raw ultrafast electron scattering (UES) data and interactively exploring the processed data. The first package, iris, is graphical user-interface program and library for interactive exploration of UES data. Under the hood, iris makes use of npstreams, an extensions of numpy to streaming array-processing, for high-throughput parallel data reduction. Finally, we present scikit-ued, a library of reusable routines and data structures for analysis of UES data, including specialized image processing algorithms, simulation routines, and crystal structure manipulation operations. In this paper, some of the features or all three packages are highlighted, such as parallel data reduction, image registration, interactive exploration. The packages are fully tested and documented and are released under permissive licenses.
关键词： Ultrafast electron scattering,Visualization,Data processing,Open-source
更新于2025-09-19 17:15:36
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Symmetric Ultrafast Writing and Erasing Speeds in Quasi-Nonvolatile Memory via van der Waals Heterostructures
摘要： Due to the large gap in timescale between volatile memory and nonvolatile memory technologies, quasi-nonvolatile memory based on 2D materials has become a viable technology for filling the gap. By exploiting the elaborate energy band structure of 2D materials, a quasi-nonvolatile memory with symmetric ultrafast write-1 and erase-0 speeds and long refresh time is reported. Featuring the 2D semifloating gate architecture, an extrinsic p–n junction is used to charge or discharge the floating gate. Owing to the direct injection or recombination of charges from the floating gate electrode, the erasing speed is greatly enhanced to nanosecond timescale. Combined with the ultrafast write-1 speed, symmetric ultrafast operations on the nanosecond timescale are achieved, which are ≈106 times faster than other memories based on 2D materials. In addition, the refresh time after a write-1 operation is 219 times longer than that of dynamic random access memory. This performance suggests that quasi-nonvolatile memory has great potential to decrease power consumption originating from frequent refresh operations, and usher in the next generation of high-speed and low-power memory technology.
关键词： symmetric ultrafast operations,van der Waals heterostructures,quasi-nonvolatile memory
更新于2025-09-19 17:15:36
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Decomposing Electronic and Lattice Contributions in Optical Pump–X-ray Probe Transient Inner-Shell Absorption Spectroscopy of CuO
摘要： Electronic and lattice contributions to picosecond time-resolved X-ray absorption spectra (trXAS) of CuO at the oxygen K-edge are analyzed by comparing trXAS spectra, recorded using excitation wavelengths of 355 nm and 532 nm, to steady-state, temperature-dependent XAS measurements. The trXAS spectra at pump-probe time-delays ≥150 ps are dominated by lattice heating effects. Insight into the temporal evolution of lattice temperature profiles on timescales up to 100’s of nanoseconds after laser excitation are reported, on an absolute temperature scale, with a temporal sensitivity and a spatial selectivity on the order of 10’s of picoseconds and 10’s of nanometers, respectively, effectively establishing an 'ultrafast thermometer'. In particular, for the 532 nm experiment at ~5 mJ/cm2 fluence, both the initial sample temperature and its dynamic evolution are well captured by a one-dimensional thermal energy deposition and diffusion model. The thermal conductivity k = (1.3±0.4) W m–1 K–1 derived from this model is in good agreement with the literature value for CuO powder kpowder = 1.013 W m–1 K–1. For 355 nm excitation, a quantitative analysis of the experiments is hampered by the large temperature gradients within the probed sample volume owing to the small UV penetration depth. The impact of the findings on mitigating or utilizing photoinduced lattice temperature changes in future X-ray free electron laser (XFEL) experiments is discussed.
关键词： X-ray absorption spectroscopy,Ultrafast X-ray spectroscopy,CuO,lattice heating,thermal conductivity
更新于2025-09-19 17:15:36
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Lighting Up Invisible Twisted Intramolecular Charge Transfer State by High Pressure
摘要： The twisted intramolecular charge transfer (TICT) state plays an important role in determining the performance of optoelectronic devices. However, for some non-fluorescent TICT molecules, 'invisible' TICT state could only be visualized by modifying the molecular structure. Here, we introduce a new facile pressure-induced approach to light up the TICT state through the use of the pressure related liquid–solid phase transition of the surrounding solvent. Combining ultrafast spectroscopy and quantum chemical calculations, it reveals that the 'invisible' TICT state can emit fluorescence when the rotation of a donor group is restricted by the frozen acetonitrile solution. Furthermore, the TICT process can even be effectively regulated by the external pressure. Our study offers a unique strategy to achieve dual fluorescence behavior in charge transfer molecules and is of significance for optoelectronic and biomedical applications.
关键词： Dual fluorescence,Twisted intramolecular charge transfer,High pressure,Ultrafast spectroscopy
更新于2025-09-19 17:15:36
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RECENT ADVANCES IN ULTRAFAST TIME-RESOLVED SCANNING TUNNELING MICROSCOPY
摘要： Making smaller and faster functional devices has led to an increasing demand for a microscopic technique that allows the investigation of carrier and phonon dynamics with both high spatial and temporal resolutions. Traditional optical pump–probe methods can achieve femtosecond temporal resolution but fall short in the spatial resolution due to the diffraction limit. Scanning tunneling microscopy (STM), on the contrary, has realized atomic-scale spatial resolution relying on the high sensitivity of the tunneling current to the tip-sample distance. However, limited by the electronics bandwidth, STM can only push the temporal resolution to the microseconds scale, restricting its applications to probe various ultrafast dynamic processes. The combination of these two methods takes advantages of optical pump–probe techniques and highly localized tunneling currents of STM, providing one viable solution to track atomic-scale ultrafast dynamics in single molecules and low-dimensional materials. In this review, we will focus on several ultrafast time-resolved STM methods by coupling the tunneling junctions with pulsed electric waves, THz, near-infrared and visible laser. Their applications to probe the carrier dynamics, spin dynamics, and molecular motion will be highlighted. In the end, we will present an outlook on the challenges and new opportunities in this field.
关键词： terahertz technique,femtosecond laser,Scanning tunneling microscopy,pump-probe technique,ultrafast dynamics.
更新于2025-09-19 17:15:36
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High-flux ultrafast extreme-ultraviolet photoemission spectroscopy at 18.4?MHz pulse repetition rate
摘要： Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 × 10^5 photons per pulse in the 25-to-60-eV range, releasing 1 × 10^10 photoelectrons per second from a 10-μm-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology.
关键词： attosecond science,photoelectron spectroscopy,high-harmonic generation,cavity enhancement,ultrafast lasers
更新于2025-09-19 17:15:36
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[OSA CLEO: Science and Innovations - San Jose, California (2014..-..)] CLEO: 2014 - Arbitrary Carrier-Envelope Phase Control in a 10 kHz, mJ-Class Amplifier
摘要： The carrier-envelope phase of every single shot emitted by a 10 kHz, mJ-class amplifier is measured with a fast spectrometer. A novel high-speed actuator allows arbitrary phase control, with closed-loop integrated phase noise on seed oscillator level (98 mrad, 5.10^5 shots, 50 s).
关键词： Laser amplifiers,Carrier-envelope phase,Ultrafast lasers,Phase control,Amplifier
更新于2025-09-19 17:15:36