126 research outputs found
Slingshot non-sequential double ionization as a gate to anti-correlated two electron escape
At intensities below-the-recollision threshold, we show that
re-collision-induced excitation with one electron escaping fast after
re-collision and the other electron escaping with a time delay via a Coulomb
slingshot motion is one of the most important mechanisms of non-sequential
double ionization, for strongly-driven He at 400 nm. Slingshot-NSDI is a
general mechanism present for a wide range of low intensities and pulse
durations. Anti-correlated two-electron escape is its striking hallmark. This
mechanism offers an alternative explanation of anti-correlated two-electron
escape obtained in previous studies.Comment: 6 pages, 3 figure
Sequential single-photon and direct two-photon absorption processes for Xe interacting with attosecond XUV pulses
We investigate the interaction of Xe with isolated attosecond XUV pulses.
Specifically, we calculate the ion yields and determine the pathways leading to
the formation of ionic charged states up to Xe. To do so, in our
formulation we account for single-photon absorption, sequential multi-photon
absorption, direct two-photon absorption, single and double Auger decays, and
shake-off. We compare our results for the ion yields and for ion yield ratios
with recent experimental results obtained for 93 eV and 115 eV attosecond XUV
pulses. In particular, we investigate the role that a sequence of two
single-photon ionization processes plays in the formation of Xe. We find
that each one of these two processes ionizes a core electron and thus leads to
the formation of a double core-hole state. Remarkably, we find that the
formation of Xe involves a direct two-photon absorption process and the
absorption of a total of three photons.Comment: 8 pages, 4 figure
Energy bunching in soft recollisions revealed with long-wavelength few-cycle pulses
Soft recollisions are laser-driven distant collisions of an electron with its
parent ion. Such collisions may cause an energy bunching, since electrons with
different initial drift momenta can acquire impacts, which exactly
counterbalance these differences. The bunching generates a series of peaks in
the photo-electron spectrum. We will show that this series could be uncovered
peak-by-peak experimentally by means of phase-stabilized few-cycle pulses with
increasing duration.Comment: 8 pages, 3 figure
Two-color ionization of hydrogen by short intense pulses
Photoelectron energy spectra resulting by the interaction of hydrogen with
two short pulses having carrier frequencies, respectively, in the range of the
infrared and XUV regions have been calculated. The effects of the pulse
duration and timing of the X-ray pulse on the photoelectron energy spectra are
discussed. Analysis of the spectra obtained for very long pulses show that
certain features may be explained in terms of quantum interferences in the time
domain. It is found that, depending on the duration of the X-ray pulse, ripples
in the energy spectra separated by the infrared photon energy may appear.
Moreover, the temporal shape of the low frequency radiation field may be
inferred by the breadth of the photoelectron energy spectra.Comment: 12 pages, 8 figure
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
Single-shot carrier-envelope-phase measurement in ambient air
The ability to measure and control the carrier envelope phase (CEP) of
few-cycle laser pulses is of paramount importance for both frequency metrology
and attosecond science. Here, we present a phase meter relying on the
CEP-dependent photocurrents induced by circularly polarized few-cycle pulses
focused between electrodes in ambient air. The new device facilitates compact
single-shot, CEP measurements under ambient conditions and promises CEP tagging
at repetition rates orders of magnitude higher than most conventional CEP
detection schemes as well as straightforward implementation at longer
wavelengths
Steering proton migration in hydrocarbons using intense few-cycle laser fields
Proton migration is a ubiquitous process in chemical reactions related to
biology, combustion, and catalysis. Thus, the ability to control the movement
of nuclei with tailored light, within a hydrocarbon molecule holds promise for
far-reaching applications. Here, we demonstrate the steering of hydrogen
migration in simple hydrocarbons, namely acetylene and allene, using
waveform-controlled, few-cycle laser pulses. The rearrangement dynamics are
monitored using coincident 3D momentum imaging spectroscopy, and described with
a quantum-dynamical model. Our observations reveal that the underlying control
mechanism is due to the manipulation of the phases in a vibrational wavepacket
by the intense off-resonant laser field.Comment: 5 pages, 4 figure
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Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses
We investigate the carrier-envelope phase (CEP) and intensity dependence of the longitudinal momentum distribution of photoelectrons resulting from above threshold ionization of argon by few-cycle laser pulses. The intensity of the pulses with a center wavelength of 750 nm is varied in a range between 0.7 × 1014 and . Our measurements reveal a prominent maximum in the CEP-dependent asymmetry at photoelectron energies of 2 U P (U P being the ponderomotive potential), that is persistent over the entire intensity range. Further local maxima are observed around 0.3 and 0.8 U P. The experimental results are in good agreement with theoretical results obtained by solving the three-dimensional time-dependent Schrödinger equation. We show that for few-cycle pulses, the amplitude of the CEP-dependent asymmetry provides a reliable measure for the peak intensity on target. Moreover, the measured asymmetry amplitude exhibits an intensity-dependent interference structure at low photoelectron energy, which could be used to benchmark model potentials for complex atoms
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