102 research outputs found
Attosecond nanoplasmonic streaking of localized fields near metal nanospheres
Collective electron dynamics in plasmonic nanosystems can unfold on
timescales in the attosec- ond regime and the direct measurements of plasmonic
near-field oscillations is highly desirable. We report on numerical studies on
the application of attosecond nanoplasmonic streaking spectroscopy to the
measurement of collective electron dynamics in isolated Au nanospheres. The
plasmonic field oscillations are induced by a few-cycle NIR driving field and
are mapped by the energy of photoemitted electrons using a synchronized,
time-delayed attosecond XUV pulse. By a detailed analysis of the amplitudes and
phase shifts, we identify the different regimes of nanoplasmonic streaking and
study the dependence on particle size, XUV photoelectron energy and emission
position. The simulations indicate that the near-fields around the
nanoparticles can be spatio-temporally reconstructed and may give detailed
insight into the build-up and decay of collective electron motion.Comment: Revised versio
Ultrafast Dynamic Metallization of Dielectric Nanofilms by Strong Single-Cycle Optical Fields
We predict a dynamic metallization effect where an ultrafast (single-cycle)
optical pulse with a field less or on the order of 1 V/Angstrom causes
plasmonic metal-like behavior of a dielectric film with a few-nm thickness.
This manifests itself in plasmonic oscillations of polarization and a
significant population of the conduction band evolving on a femtosecond time
scale. These phenomena are due a combination of both adiabatic (reversible) and
diabatic (for practical purposes irreversible) pathways.Comment: 4 pages, 4 figure
Nanoplasmonic near-field synthesis
The temporal response of resonances in nanoplasmonic structures typically
converts an incoming few-cycle field into a much longer near-field at the spot
where non-linear physical phenomena including electron emission, recollision
and high-harmonic generation can take place. We show that for practically
useful structures pulse shaping of the incoming pulse can be used to synthesize
the plasmon-enhanced field and enable single-cycle driven nonlinear physical
phenomena. Our method is demonstrated for the generation of an isolated
attosecond pulse by plasmon-enhanced high harmonic generation. We furthermore
show that optimal control techniques can be used even if the response of the
plasmonic structure is not known a priori.Comment: 6 page
Predicted Ultrafast Dynamic Metallization of Dielectric Nanofilms by Strong Single-Cycle Optical Fields
We predict a dynamic metallization effect where an ultrafast (single-cycle) optical pulse with a ≲1 V/Åfield causes plasmonic metal-like behavior of a dielectric film with a few-nm thickness. This manifests itself in plasmonic oscillations of polarization and a significant population of the conduction band evolving on a ∼1 fs time scale. These phenomena are due to a combination of both adiabatic (reversible) and diabatic (for practical purposes irreversible) pathways
Non-sequential double ionization with near-single cycle laser pulses
A three-dimensional semiclassical model is used to study double ionization of Ar when driven by a near-infrared and near-single-cycle laser pulse for intensities ranging from 0.85 x 10(14) W/cm(2) to 5 x 10(14) W/cm(2). Asymmetry parameters, distributions of the sum of the two electron momentum components along the direction of the polarization of the laser field and correlated electron momenta are computed as a function of the intensity and of the carrier envelope phase. A very good agreement is found with recently obtained results in kinematically complete experiments employing near-single-cycle laser pulses. Moreover, the contribution of the direct and delayed pathways of double ionization is investigated for the above observables. Finally, an experimentally obtained anti-correlation momentum pattern at higher intensities is reproduced with the three-dimensional semiclassical model and shown to be due to a transition from strong to soft recollisions with increasing intensity
Ion microscopy with evolutionary-algorithm-based autofocusing
Ion microscopy is an established technique for laser focus diagnostics and the accurate, intensity-resolved measurement of laser ionization processes. In the present feasibility study, we discuss a new ion microscope design, which improves its resolution across a large range of magnifications and simplifies its operation. Instead of the common two einzel lens configuration, which is usually optimized for a fixed magnification, we propose a generic design consisting of an array of equally spaced ring electrodes, whose individually adjustable voltages are controlled by an evolutionary algorithm. In this way, we can realize aberration minimized magnifications between 25 and 100. Moreover, the algorithm can adjust the voltage settings under changing experimental conditions and facilitates autofocusing for user-defined magnification
Reaction Nanoscopy of Ion Emission from Sub-wavelength Propanediol Droplets
Droplets provide unique opportunities for the investigation of laser-induced
surface chemistry. Chemical reactions on the surface of charged droplets are
ubiquitous in nature and can provide critical insight into more efficient
processes for industrial chemical production. Here, we demonstrate the
application of the reaction nanoscopy technique to strong-field ionized
nanodroplets of propanediol (PDO). The technique's sensitivity to the
near-field around the droplet allows for the in-situ characterization of the
average droplet size and charge. The use of ultrashort laser pulses enables
control of the amount of surface charge by the laser intensity. Moreover, we
demonstrate the surface chemical sensitivity of reaction nanoscopy by comparing
droplets of the isomers 1,2-PDO and 1,3-PDO in their ion emission and
fragmentation channels. Referencing the ion yields to gas-phase data, we find
an enhanced production of methyl cations from droplets of the 1,2-PDO isomer.
Density functional theory simulations support that this enhancement is due to
the alignment of 1,2-PDO molecules on the surface. The results pave the way
towards spatio-temporal observations of charge dynamics and surface reactions
on droplets in pump-probe studies
Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields
Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D+ and Cl+ fragments were recorded via velocity-map imaging. A waveformdependent anti-correlated directional emission of D+ and Cl+ fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl+ and in turn the directional emission of charged fragments upon the breakup of the molecular ion
Lightwave-controlled band engineering in quantum materials
Stacking and twisting atom-thin sheets create superlattice structures with
unique emergent properties, while tailored light fields can manipulate coherent
electron transport on ultrafast timescales. The unification of these two
approaches may lead to ultrafast creation and manipulation of band structure
properties, which is a crucial objective for the advancement of quantum
technology. Here, we address this by demonstrating a tailored lightwave-driven
analogue to twisted layer stacking. This results in sub-femtosecond control of
time-reversal symmetry breaking and thereby band structure engineering in a
hexagonal boron nitride monolayer. The results practically demonstrate the
realization of the topological Haldane model in an insulator. Twisting the
lightwave relative to the lattice orientation enables switching between band
configurations, providing unprecedented control over the magnitude and location
of the band gap, and curvature. A resultant asymmetric population at
complementary quantum valleys lead to a measurable valley Hall current,
detected via optical harmonic polarimetry. The universality and robustness of
the demonstrated sub-femtosecond control opens a new way to band structure
engineering on the fly paving a way towards large-scale ultrafast quantum
devices for real-world applications.Comment: 4 pages main text, 4 figure
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