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Q 5 Ultrakurze Lichtimpulse: Attosekundenpulse
Zeit: Montag 14:00–15:45 Raum: HS 223
Gruppenbericht Q 5.1 Mo 14:00 HS 223
Direct measurement of attosecond pulse trains — •K. Witte 1 ,
P. Tzallas 1 , D. Charalambidis 2 , N. Papadogiannis 2 , and G.
Tsakiris 1 — 1 Max-Planck-Institut für Quantenoptik, D-85748 Garching,
Germany — 2 Foundation for Research and Technology - Hellas, Institute
of Electronic Structure & Laser, PO Box 1527, GR-711 10 Heraklion
(Crete), Greece and Department of Physics, University of Crete,
P.O. Box 2208, GR-71003 Voutes-Heraklion (Crete), Greece
The most widely used method for the pulse duration measurement of
pico- and femtosecond laser pulses is the second-order auto-correlation
(AC) technique, which relies on a non-linear effect induced solely by the
radiation to be characterized. Employing appropriate modifications, we
have succeeded in extending this approach to a coherent superposition of
harmonics thus demonstrating the feasibility of performing second-order
AC measurement with sub-femtosecond XUV pulses. The experimental
results bear direct evidence that a synthesis of five harmonics (7th to
15th) produced in a Xe gas jet gives rise to an XUV signal exhibiting
clear attosecond structure with periodicity twice that of the driving laser
field [1]. While the unique capabilities of this new approach are demonstrated
here in performing the first AC measurement of an attosecond
pulse train, the method itself initiates the XUV-pump - XUV-probe studies
in sub-femtosecond scale dynamics. References [1] P. Tzallas et al.,
Nature 426, 267(2003)
Q 5.2 Mo 14:30 HS 223
Time Resolved Autoionization — •M. Wickenhauser 1 , J. Burgdoerfer
1 , F. Krausz 2 , and M. Drescher 3 — 1 Inst. for Theoretical
Physics, Vienna University of Technology — 2 Photonics Inst., Vienna
University of Technology — 3 Faculty of Physics, University of Bielefeld
Recent experiments have succeded in tracing the time evolution of an
Auger decay with a decay time of 8 fs with attosecond resolution. We investigate
the feasibility to implement the same pump probe technique to
study time-resolved autoionization. A time-resolved autoionization process
is initialized by a short XUV-pump pulse (¯hω ∼ 50 − 100 eV) in the
presence of a synchronized probe laser pulse (¯hω ∼ 1.6 eV). Excitation
with the pump pulse opens two interfering paths from the ground state to
the continuum. The time evolution of the coherent superposition of resonant
state and continuum is mapped onto a modulation of the electron
spectrum as a function of the time delay between pump and probe pulse.
Without probe laser the spectrum shows the typical Beutler-Fano profile.
In the presence of the probe pulse periodical fluctuations and sidebands
in the energy spectrum provide information about the time evolution of
the autoionization process. Furthermore we have found that in the case
of complex Fanoparameters time-resolved experiments provide more information
than time-integral measurements. Possible candidates to test
our predictions are (Super-) Coster Kronig transitions with lifetimes of
the order of 500 as. This method holds the promise to resolve complex
atomic dynamics on the attosecond scale.
Work supported by the Austrian FWF, proj. No. SFB016.
Q 5.3 Mo 14:45 HS 223
Single-shot dynamics of pulses from a gas-filled hollow fiber —
•Jens Biegert, Mathis Bruck, Wouter Kornelis, Florian Helbing,
Christoph Hauri, and Ursula Keller — Physik Department,
Swiss Federal Institute of Technology (ETH), Zürich, Switzerland
Gas-filled hollow fibers are indispensable to generate high-energy fewcycle
pulses as e.g. required for the generation of single attosecond XUV
pulses. The generation is extremely sensitive to the pulse parameters
and therefore we have measured, single-shot, simultaneously and at 1
kHz: the input and output energies and spectra together with the input
beam pointing and fully characterized the input pulse with SPIDER. Preliminary
results show, with negligible beam pointing fluctuations of 0.3
strongly varying broadened output spectrum exhibiting significant shifts
80
in the output center frequency with input energy and spectral phase,
which has clear implications e.g. for the properties of generated highharmonics.
Q 5.4 Mo 15:00 HS 223
Anwendung einer Quelle für Hohe-Harmonischen Strahlung bei
13 nm Wellenlänge — •Rolf Früke 1 , Tobias Witting 2 , Jörg
Kutzner 2 , Helmut Zacharias 2 und Thomas Wilhein 1 für die -
Kollaboration — 1 Fachhochschule Koblenz, RheinAhrCampus Remagen,
Südallee 2, D-53424 Remagen — 2 Westfälische Wilhelms-Universität
Münster, Physikalisches Institut, Wilhelm-Klemm-Straße 10, D-48149
Münster
Quellen für Licht im extrem Ultravioletten und weichen Röntgenbereich
finden ihre Anwendung in der Lithografie und der Mikroskopie.
Quellen für Strahlung hoher Harmonischer bieten eine Möglichkeit, diesen
Spektralbereich auf kleinem Raum im Labor zur Verfügung zu stellen.
Zur Anregung hoher Harmonischer wird ein 1kHz Ti:Saphir Lasersystem
(∆τ ≈ 30fs) mit einer Zentralwellenlänge von 800nm verwendet.
Die Quelle wurde mit Neon bei 13nm Wellenlänge (61.Harmonische)
betrieben und die Auswirkung auf das Harmonischen Spektrum bei Einstellen
eines chirps des fundamentalen Laserpulses beobachtet. Weiter
wurden Experimente zur Abbildung mit einer Zonenplatte in Verbindung
mit einem Multilayer-Monochromator durchgeführt. Als Detektor
wurde eine rückseitig gedünnte CCD-Kamera verwendet.
Q 5.5 Mo 15:15 HS 223
Hohe Harmonische als Attosekunden-Probe-Signal für Vibrationsdynamik
— •Manfred Lein — Max-Planck-Institut für Physik
komplexer Systeme, Nöthnitzer Straße 38, 01187 Dresden
Moleküle in starken Laserpulsen emittieren hohe Harmonische, d.h.
kohärente UV-Strahlung. Nicht-Born-Oppenheimer-Rechnungen für H2
und D2 zeigen, dass die Emissionsspektren Aufschluss über die laserinduzierte
Vibrationsbewegung des Moleküls geben. Unter geeigneten Bedingungen
(im Wesentlichen genügend lange Laserwellenlänge) dienen
einzelne Harmonische als Probe-Signale zu unterschiedlichen Zeiten. In
diesem Fall kann die Vibration, genauer die Autokorrelationsfunktion des
Vibrationswellenpakets, auf einer Sub-Femtosekunden-Zeitskala verfolgt
werden.
Q 5.6 Mo 15:30 HS 223
Towards Attosecond Half-Cycle Pulses — •Emil Persson 1 , Severin
Puschkarski 1 , Xiao-Min Tong 2 , and Joachim Burgdörfer 1
— 1 Institute for Theoretical Physics, Vienna University of Technology —
2 Department of Physics, Kansas State University
Present techniques for producing half-cycle pulses (HCP) are limited
to widths of 500fs, which limits impulsely shaping and manipulating of
wave packets to Rydberg states n ≫ 1. We theoretically analyze a protocol
for producing HCP in the attosecond regime [1]. Such pulses in
a pump-probe setting would allow to impulsely drive, probe, shape and
control electronic wave functions near the ground state [2].
We study the harmonics generated by the non-linear interaction of an
atom with strong two-color fields (HHG) in single atom response. To
form HCP, the phases of all harmonics, starting from the fundamental,
should be aligned. Varying the strength and amplitudes of the two-color
driving field, we find that it is possible to align the phases of the lowest
harmonics up to the energy necessary to excite the first higher state. For
helium we find HCP with a width as short as 280as.
Depending on the length and carrier-envelope phase of the driving field,
we find (a) trains consisting of hundreds of HCP, (b) single HCP with
only small side-wings, and (c) trains consisting of two HCP with variable
strengths and delay between the pulses. The findings (b, c) imply
possibilities for attosecond impulsive pump-probe experiments.
Work supported by the Austrian FWF under contract No. SFB-016