50 research outputs found
Intense keV isolated attosecond pulse generation by orthogonally polarized multicycle midinfrared two-color laser field
We theoretically investigate the generation of intense keV attosecond pulses
in an orthogonally polarized multicycle midinfrared two-color laser field. It
is demonstrated that multiple continuum-like humps, which have a spectral width
of about twenty orders of harmonics and an intensity of about one order higher
than adjacent normal harmonic peaks, are generated under proper two-color
delays, owing to the reduction of the number of electron-ion recollisions and
suppression of inter-half-cycle interference effect of multiple electron
trajectories when the long wavelength midinfrared driving field is used. Using
the semiclassical trajectory model, we have revealed the two-dimensional
manipulation of the electron-ion recollision process, which agrees well with
the time frequency analysis. By filtering these humps, intense isolated
attosecond pulses are directly generated without any phase compensation. Our
proposal provides a simple technique to generate intense isolated attosecond
pulses with various central photon energies covering the multi-keV spectral
regime by using multicycle driving pulses with high pump energy in experiment.Comment: 11 pages,5 figures, research articl
Direct evidences for inner-shell electron-excitation by laser induced electron recollision
Extreme ultraviolet (XUV) attosecond pulses, generated by a process known as
laser-induced electron recollision, are a key ingredient for attosecond
metrology, providing a tool to precisely initiate and probe sub-femtosecond
dynamics in the microcosms of atoms, molecules and solids[1]. However, with the
current technology, extending attosecond metrology to scrutinize the dynamics
of the inner-shell electrons is a challenge, that is because of the lower
efficiency in generating the required soft x-ray \hbar\omega>300 eV attosecond
bursts and the lower absorption cross-sections in this spectral range. A way
around this problem is to use the recolliding electron to directly initiate the
desired inner-shell process, instead of using the currently low flux x-ray
attosecond sources.Such an excitation process occurs in a sub-femtosecond
timescale, and may provide the necessary "pump" step in a pump-probe
experiment[2]. Here we used a few cycle infrared \lambda_{0}~1800nm source[3]
and observed direct evidences for inner-shell excitations through the
laser-induced electron recollision process. It is the first step toward
time-resolved core-hole studies in the keV energy range with sub-femtosecond
time resolution.Comment: 6 pages, 4 figure
Mapping the spectral phase of isolated attosecond pulses by extreme-ultraviolet emission spectrum
An all-optical method is proposed for the measurement of the
spectral phase of isolated attosecond pulses. The technique is based on the
generation of extreme-ultraviolet (XUV) radiation in a gas by the
combination of an attosecond pulse and a strong infrared (IR) pulse with
controlled electric field. By using a full quantum simulation, we
demonstrate that, for particular temporal delays between the two pulses, the
IR field can drive back to the parent ions the photoelectrons generated by
the attosecond pulse, thus leading to the generation of XUV photons. It is
found that the generated XUV spectrum is notably sensitive to the chirp of
the attosecond pulse, which can then be reliably retrieved. A classical
quantum-path analysis is further used to quantitatively explain the main
features exhibited in the XUV emission
Waveform-Controlled Terahertz Radiation from the Air Filament Produced by Few-Cycle Laser Pulses
Waveform-controlled Terahertz (THz) radiation is of great importance due to
its potential application in THz sensing and coherent control of quantum
systems. We demonstrated a novel scheme to generate waveform-controlled THz
radiation from air plasma produced when carrier-envelope-phase (CEP) stabilized
few-cycle laser pulses undergo filamentation in ambient air. We launched
CEP-stabilized 10 fs-long (~ 1.7 optical cycles) laser pulses at 1.8 {\mu}m
into air and found that the generated THz waveform can be controlled by varying
the filament length and the CEP of driving laser pulses. Calculations using the
photocurrent model and including the propagation effects well reproduce the
experimental results, and the origins of various phase shifts in the filament
are elucidated.Comment: 5pages, 5 figure
Laser-induced inner-shell excitations through direct electron re-collision versus indirect collision
The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Intestinal Microbiota-Derived GABA Mediates Interleukin-17 Expression during Enterotoxigenic Escherichia coli Infection
Intestinal microbiota has critical importance in pathogenesis of intestinal infection; however, the role of intestinal microbiota in intestinal immunity during enterotoxigenic Escherichia coli (ETEC) infection is poorly understood. The present study tested the hypothesis that the intestinal microbiota is associated with intestinal interleukin-17 (IL-17) expression in response to ETEC infection. Here, we found ETEC infection induced expression of intestinal IL-17 and dysbiosis of intestinal microbiota, increasing abundance of γ-aminobutyric acid (GABA)-producing Lactococcus lactis subsp. lactis. Antibiotics treatment in mice lowered the expression of intestinal IL-17 during ETEC infection, while GABA or L. lactis subsp. lactis administration restored the expression of intestinal IL-17. L. lactis subsp. lactis administration also promoted expression of intestinal IL-17 in germ-free mice during ETEC infection. GABA enhanced intestinal IL-17 expression in the context of ETEC infection through activating mechanistic target of rapamycin complex 1 (mTORC1)-ribosomal protein S6 kinase 1 (S6K1) signaling. GABA–mTORC1 signaling also affected intestinal IL-17 expression in response to Citrobacter rodentium infection and in drug-induced model of intestinal inflammation. These findings highlight the importance of intestinal GABA signaling in intestinal IL-17 expression during intestinal infection and indicate the potential of intestinal microbiota-GABA signaling in IL-17-associated intestinal diseases
The Impact of the Regional Military Conflict in Global Stock and Commodity Market
As the crisis between Russia and Ukraine erupted, a certain degree of geopolitical risk has been triggered, which caused a significant impact on the global economy. The transmission mechanism of geopolitical risks is complex, and factors that may cause market volatility risks include trade factors, investor sentiment, relevant policies and so forth. This article will combine previous research findings and existing market data to explore the impact of the Russia-Ukraine conflict on the stock and commodity markets. Besides, it will also interpret the possible risk transmission mechanisms and consequences behind it based on statistics facts. The study found that this event had a disastrous effect on both the stock and commodity markets, but the specific direction and intensity of the fluctuations vary depending on the research subject. This article summarizes some previous research and provides a summary of the global economic impact of the Russia-Ukraine conflict and gives some suggestions to investors
Attosecond photoionization for reconstruction of bound-electron wave packets
We present a method for the characterization of bound-electron wave packets generated by a broadband
excitation pulse. The technique is based on the photoionization of the electron wave packet by a delayed isolated
attosecond pulse and on the measurement of the ionization asymmetry parameter in the direction of the probe
pulse polarization, which depends on the pump-probe delay and on the photoelectron energy. By numerically
solving the fully three-dimensional time-dependent Schr¨odinger equation we show that Fourier analysis of the
two-dimensional ionization asymmetry parameter, displaying a complex interference pattern, enables a clear
observation of quantum beats between pairs of stationary states involved in the generation of the wave packet.
An analytical model confirms that the quantum beats’ signal encodes the weight of each stationary state, thus
suggesting a feasible approach for the complete characterization of the relative population ratio of the excited-state
components of thewave packet. Moreover, an approach based on the further analysis of quantum beats is proposed
to retrieve the lifetime added to each excited state