30 research outputs found
Real-time probing electron dynamics of an atom in a strong infrared laser field
We present theoretical studies on real-time probing the electron density
evolution of an atom in a strong infrared (IR) laser field with few-cycle
near-infrared (NIR) and attosecond extreme-ultraviolet (XUV) pulses. Our
results indicate that the electron density near the tunneling barrier is
reflected in the additional tunneling ionization yield with a delayed NIR pulse
and the electron density near the nucleus can be probed by the single
photoionization yield with a delayed XUV pulse. It turns out the NIR-probing
scheme can be used to study the polarization of the system in an external IR
field and the XUV-probing can be additionally applied to explore excitation
dynamics during and after the IR field interaction
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
Tunable sub-20 fs pulses from a 500 kHz OPCPA with 15 W average power based on an all-ytterbium laser
An optical parametric chirped pulse amplifier fully based on Yb lasers at 500
kHz is described. Passive optical-synchronization is achieved between a fiber
laser-pumped white-light and a 515 nm pump produced with a 200 W picosecond
Yb:YAG InnoSlab amplifier. An output power up to 19.7 W with long-term
stability of 0.3% is demonstrated for wavelength tunable pulses between 680 nm
and 900 nm and spectral stability of 0.2%; 16.5 W can be achieved with a
bandwidth supporting 5.4 fs pulses. We demonstrate compression of 30 microjoule
pulses to sub-20 fs duration with a prism compressor, suitable for high
harmonic generation.Comment: 4 pages, 4 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
Dynamics of the photoinduced insulator-to-metal transition in a nickelate film
The control of materials properties with light is a promising approach
towards the realization of faster and smaller electronic devices. With phases
that can be controlled via strain, pressure, chemical composition or
dimensionality, nickelates are good candidates for the development of a new
generation of high performance and low consumption devices. Here we analyze the
photoinduced dynamics in a single crystalline NdNiO film upon excitation
across the electronic gap. Using time-resolved reflectivity and resonant x-ray
diffraction, we show that the pump pulse induces an insulator-to-metal
transition, accompanied by the melting of the charge order. Finally we compare
our results to similar studies in manganites and show that the same model can
be used to describe the dynamics in nickelates, hinting towards a unified
description of these photoinduced phase transitions.Comment: 17 pages, 6 figure
Excited-state band structure mapping
[EN] Angle-resolved photoelectron spectroscopy is an extremely powerful probe of materials to access the occupied electronic structure with energy and momentum resolution. However, it remains blind to those dynamic states above the Fermi level that determine technologically relevant transport properties. In this work we extend band structure mapping into the unoccupied states and across the entire Brillouin zone by using a state-of-the-art high repetition rate, extreme ultraviolet femtosecond light source to probe optically excited samples. The wideranging applicability and power of this approach are demonstrated by measurements on the two-dimensional semiconductor WSe2, where the energy-momentum dispersion of valence and conduction bands are observed in a single experiment. This provides a direct momentum-resolved view, not only on the complete out-of-equilibrium band gap but also on its renormalization induced by electronic screening. Our work establishes a benchmark for measuring the band structure of materials, with direct access to the energy-momentum dispersion of the excited-state spectral function.A This work was funded by the Max-Planck-Gesellschaft, by the German Research Foundation (DFG) , within the Emmy Noether Program (Grant No. RE 3977/1) , and Grants No. FOR1700 (Project E5) , No. SPP2244 (Project No. 443366970) , and from the European Research Council, Grant ERC-2015-CoG-682843. M.P. acknowledges financial support from the Swiss National Science Foundation (SNSF) through Grant No. CRSK-2_196756. C.W.N. and C.M. ac-knowledge financial support by Swiss National Science Foundation (SNSF) Grant No. P00P2_170597. A.R. and H.H. acknowledge financial support from the European Research Council (Grant No. ERC-2015-AdG-694097) and the Cluster of Excellence "CUI: Advanced Imaging of Matter" of the Deutsche Forschungsgemeinschaft (Grant EXC 2056, Project No. 390715994)
Dynamics of the photoinduced insulator-to-metal transition in a nickelate film
Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions. © 2018 Author(s)
Compact and robust supercontinuum generation and post-compression using multiple thin plates
We report on compact and robust supercontinuum generation and post-compression using transmission of light through multiple thin solid plates at the SwissFEL X-ray free-electron laser facility. A single stage consisting of three thin plates followed by a chirped mirror compressor achieves compression of initially 30-fs pulses with 800-nm center wavelength to sub-10-fs duration. We also demonstrate a two-stage implementation to compress the pulses further to sub-5-fs duration. With the two-stage setup, the generated supercontinuum includes wavelengths ranging from 500 to 1100 nm. The multiplate setup is compact, robust, and stable, which makes it ideal for applications at free-electron laser facilities such as pump-probe experiments and laser-arrival timing tools.ISSN:2095-4719ISSN:2052-328
Generation of millijoule-level sub-5 fs violet laser pulses
We demonstrate the generation, spectral broadening and post-compression of second harmonic pulses using a thin beta barium borate (BBO) crystal on a fused-silica substrate as the nonlinear interaction medium. By combining second harmonic generation in the BBO crystal with self-phase modulation in the fused-silica substrate, we efficiently generate millijoule-level broadband violet pulses from a single optical component. The second harmonic spectrum covers a range from long wave ultraviolet (down to 310 nm) to visible (up to 550 nm) with a bandwidth of 65 nm. Subsequently, we compress the second harmonic beam to a duration of 4.8 fs with a pulse energy of 0.64 mJ (5 fs with a pulse energy of 1.05 mJ) using chirped mirrors. The all-solid free-space apparatus is compact, robust and pulse energy scalable, making it highly advantageous for generating intense second harmonic pulses from near-infrared femtosecond lasers in the sub-5 fs regime.ISSN:2095-4719ISSN:2052-328