108 research outputs found
Attosecond Streaking in the Water Window: A New Regime of Attosecond Pulse Characterization
We report on the first streaking measurement of water-window attosecond
pulses generated via high harmonic generation, driven by sub-2-cycle,
CEP-stable, 1850 nm laser pulses. Both the central photon energy and the energy
bandwidth far exceed what has been demonstrated thus far, warranting the
investigation of the attosecond streaking technique for the soft X-ray regime
and the limits of the FROGCRAB retrieval algorithm under such conditions. We
also discuss the problem of attochirp compensation and issues regarding much
lower photo-ionization cross sections compared with the XUV in addition to the
fact that several shells of target gases are accessed simultaneously. Based on
our investigation, we caution that the vastly different conditions in the soft
X-ray regime warrant a diligent examination of the fidelity of the measurement
and the retrieval procedure.Comment: 14 Pages, 12 figure
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Disentangling conical intersection and coherent molecular dynamics in methyl bromide with attosecond transient absorption spectroscopy
Attosecond probing of core-level electronic transitions provides a sensitive tool for studying valence molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy to follow the valence dynamics of strong-field initiated processes in methyl bromide. By probing the 3d core-to-valence transition, we resolve the strong field excitation and ensuing fragmentation of the neutral σ* excited states of methyl bromide. The results provide a clear signature of the non-adiabatic passage of the excited state wavepacket through a conical intersection. We additionally observe competing, strong field initiated processes arising in both the ground state and ionized molecule corresponding to vibrational and spin-orbit motion, respectively. The demonstrated ability to resolve simultaneous dynamics with few-femtosecond resolution presents a clear path forward in the implementation of attosecond XUV spectroscopy as a general tool for probing competing and complex molecular phenomena with unmatched temporal resolution
Wave packet retrieval by multi-photon quantum beat spectroscopy in helium
We show that we can probe the components of an attosecond bound electron wave packet by mapping the quantum beat signal produced by a synchronized delayed few-cycle infrared pulse into the continuum. In addition, spectrally overlapping peaks that result from one-, two- or three-photon processes from more or less deeply bound states can in principle be interferometrically resolved with high resolution
Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy
Non-adiabatic dynamics and conical intersections play a central role in the
chemistry of most polyatomic molecules, ranging from isomerization to
heterocyclic ring opening and avoided photo-damage of DNA. Studying the
underpinning correlated dynamics of electronic and nuclear wave packets is a
major challenge in real-time and, many times involves optically dark transient
states. We show that attosecond core-level spectroscopy reveals the pathway
dynamics of neutral furan across its conical intersections and dark states. Our
method measures electronic-nuclear correlations to detect the dephasing of
electronic coherence due to nuclear motion and identifies the ring-opened
isomer as the dominant product. These results demonstrate the efficacy of
attosecond core level spectroscopy as a potent method to investigate the
real-time dynamics of photochemical reaction pathways in complex molecular
systems
Small Scale Systems of Galaxies. III. X-ray detected E+S galaxy pairs in low density environments
We present a comprehensive study of the local environments of four E+S galaxy
pairs with the main goal to investigate their formation/evolution histories.
New XMM-Newton data were obtained for two pairs (RR 143 and RR 242) that
complements existing ROSAT data for the other two (RR 210 and RR 216). The new
observations reveal diffuse X-ray emission in both pairs. The emission is
asymmetric in both cases and extends out to 120 kpc and 160 kpc in RR 143 and
RR 242 respectively. The nucleus of RR 242 hosts a low luminosity mildly
absorbed AGN. We find that the early-type components of pairs with diffuse hot
gas appear to be relaxed objects while those in RR 210 and RR 216, where no
diffuse emission has been found, display unambiguous signatures of ongoing
interaction. Wide-field V and R-band data are used to study the photometric
properties of the early-type components and to search for a candidate faint
galaxy populations around each of the pairs. While no diffuse optical light is
found for any of the pairs, all of the early-type members show very extended
and concentric luminous envelopes. We identify a faint galaxy sample in each
field and we consider whether they could be physically associated with the
luminous pairs based upon (V-R) colors and photometric properties. We find that
the distribution of r_e and M_R for the candidates are similar in three of the
fields (RR 143, 216 and 242). The same selection criteria applied to the field
of RR 210 suggest a fainter and more compact population possibly suggesting a
larger background fraction than in the other fields.Comment: 47 pages, 18 figures, Astron. J. in pres
Revealing electronic state-switching at conical intersections in alkyl iodides by ultrafast XUV transient absorption spectroscopy
Conical intersections between electronic states often dictate the chemistry
of photoexcited molecules. Recently developed sources of ultrashort extreme
ultraviolet (XUV) pulses tuned to element-specific transitions in molecules
allow for the unambiguous detection of electronic state-switching at a conical
intersection. Here, the fragmentation of photoexcited iso-propyl iodide and
tert-butyl iodide molecules (i-CHI and t-CHI) through a
conical intersection between Q/Q spin-orbit states is
revealed by ultrafast XUV transient absorption measuring iodine 4d
core-to-valence transitions. The electronic state-sensitivity of the technique
allows for a complete mapping of molecular dissociation from photoexcitation to
photoproducts. In both molecules, the sub-100 fs transfer of a photoexcited
wave packet from the Q state into the Q state at the
conical intersection is captured. The results show how differences in the
electronic state-switching of the wave packet in i-CHI and
t-CHI directly lead to differences in the photoproduct branching
ratio of the two systems
Observation and Control of Laser-Enabled Auger Decay
Single photon laser enabled Auger decay (spLEAD) has been redicted
theoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its
first experimental observation in neon. Using coherent, bichromatic
free-electron laser pulses, we have detected the process and coherently
controlled the angular distribution of the emitted electrons by varying the
phase difference between the two laser fields. Since spLEAD is highly sensitive
to electron correlation, this is a promising method for probing both
correlation and ultrafast hole migration in more complex systems.Comment: 5 pages, 3 figure
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
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