VUVX2010, the 37th International conference on Vacuum Ultraviolet and X-ray Physics - Multi-terawatt lasers overview

Transient phases and phase transitions probed with ultrafast X-ray scattering
and spectroscopy
A Föhlisch1
1Institute for Methods and Instrumentation in Synchrotron Radiation Research G-I2 Helmholtz-Zentrum Berlin, Berlin, Germany;
2Institut für Physik und Astronomie Universität Potsdam Karl-Liebknecht-Strasse 24-25, Potsdam, Germany
Inmaterials science and femtochemistry, the frontier of knowledge spans frommolecular surface dynamics for
heterogeneous catalysis with little explored transition states to functionalmaterials with often surprising properties
and phase transitions as well as to chemical dynamics in solution. In these systems the interplay between local
properties and nanoscale phenomena govern their physics and chemistry - and femtosecond soft X-ray pulses
are ideal probes of their dynamics. With innovative X-ray sources first steps into femtosecond time resolved X-ray
methods have been taken and the new physics we can access is explored through our research of femtosecond time
resolved X-ray scattering and spectroscopy formaterials science.

Femtosecond time-resolved photoemission of layered charge-density-wave
compounds
K Rossnagel,1 S Hellmann,1 C Sohrt,1 M Kalläne,1 L Kipp,1 M Beye,2 F Sorgenfrei,2 A Föhlisch,2,3 W Wurth,2 T Rohwer,1
M Wiesenmayer,1 M Bauer1
1University of Kiel, Kiel, Germany; 2University of Hamburg, Hamburg, Germany; 3Helmholtz-Zentrum Berlin für Materialien und
Energie, Berlin, Germany
Charge-density waves (CDWs) are broken-symmetry states of low-dimensional solids that are brought about by
electron-phonon interaction. Yet, surprisingly, a clear microscopic understanding beyond this statement has not
emerged for two-dimensional systems. Here, we will look at this classical paradigm of condensedmatter physics with
femtosecond time-resolved photoelectron spectroscopy using pulsed extreme ultraviolet radiation generated by a
free-electron laser (FLASH) and a high-harmonic-generation source in Kiel. We will restrict ourselves to CDWs in two
layer compounds, in the Mott insulator 1T-TaS2 and in the possible excitonic insulator 1T-TiSe2. We will determine how
fast a CDW canmelt and how fast it approaches equilibrium after impulsive optical excitation and we will particularly
investigate whether the ultrafast vaporization and equilibration dynamics provides a key to the origin of CDWs in two
dimensions.

Measurement of demagnetization dynamics at the M edges of Ni and Fe using
a tabletop high-harmonic soft X-ray source.
R Adam,1 P Grychtol,1 C La-O-Vorakiat,2 S Mathias,3 M Siemens ,4 J Shaw ,4 H Nembach,4 T Silva ,4 M Aeschlimann,3 CM
Schneider,1 HC Kapteyn ,2 MM Murnane2
1Institute of Solid State Research, Research Centre Juelich , Juelich, Germany; 2Department of Physics and JILA,University of
Colorado, Boulder, United States; 3TU Kaiserslautern and Research Centre OPTIMAS, Kaiserslautern, Germany; 4Electromagnetics
Division, National Institute of Standards and Technology, Boulder, United States
Pump-probemeasurements based on ultrafast pulsed lasers have been the technique of choice to test the
magnetization dynamics with femtosecond temporal resolution. On the other hand, static soft X-ray experiments at
the synchrotron showed that themagnetization can be probed element-selectively by tuning the probe-beam energy
to the M absorption edges of Fe, Co, and Ni. Recently, newly developed soft X-ray sources based on the high-harmonic
up-conversion of ultrafast pulsed lasers promis to combine femtosecond temporal resolution with element-selectivity
in the single tabletop experiment. Our experiment was set up in a transversemagneto-optic Kerr effect geometry.
Reflecting laser-generated X-ray pulses off amagnetized NiFe grating largemagneto-optic signal of up to 6% at the
M absorption edges of Fe and Ni were observed. In our pump-probe experiment, short laser pump pulses were first
directed at the sample to destroy themagnetic order. Inherently synchronized X-ray probe pulses were then reflected
fromthe targeted spot tomeasure the element-specific demagnetization. Our results show a strong NiFemagnetization
reduction within 400 fs after the pump beam excitation and point towards a strong coupling of themagneticmoments
of Ni and Fe forming the NiFe film

Attosecond XUV transient absorption spectroscopy
H Wang,1 M Chini,1 S Chen,1 Z Chang1
1J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan/Kansas, United States
Time-resolved X-ray absorption spectroscopy has been demonstrated to be a powerful tool for studying phase
transitions. However, the time resolution is limited to picosecond or femtosecond at synchrotron facilities. We
have developed an experimental setup for conducting XUV/x-ray absorption with attosecond precision. Using
the double optical gatingmethod, which is a combination of polarization gating and two-color gating, a smooth
continuous spectrum covering 20 eV to 600 eV was produced with 8 fs, ~1 mJ lasers centered at 800 nm operating
at 1 kHz. The duration of the XUV pulse can be as short as 110 as. The setup consists of three parts. The first one is the
XUV generation chamber, where the laser pulse with a time-dependent ellipticity is focused on a gas target. The type
of gases used depends on the applications. For example, Xe gas is suitable for generate intense attosecond pulse in
the 20 to 30 eV photon energy range. The XUV beam is focused to the sample in the second chamber with a toroidal
mirror at grazing incident. Gas sample has been studied for far, but other types of samples can also be investigated.
The XUV beam size on the sample is ~ 30mm. A portion of 800 nm laser pulse is also focused on the sample, which
is temporally and specially overlapped with the XUV pulse. The intensity of the laser beam can reach 1014 W/cm2. A
CW green laser co-propagates with the XUV and laser beam to stabilize the path length difference between the two
beams. The delay between the XUV pulse and the laser field can be adjusted with 22 as precision. The transmitted XUV
beam wasmeasured with a transmission grating (2000 lines/mm or 5000 lines/mm) spectrometer. The spectrum
is recorded on a MCP imager and CCD camera. The spectrometer resolution is better than 80meV at 30 eV. In time
resolved experiments, the XUV spectrum ismeasured as a function of the delay between the XUV and NIR pulses. The
attosecond dynamics of Fano resonances of noble gas was studied experimentally using this setup

Using high harmonic spectroscopy to learn about molecular structure and
dynamics
DM Villeneuve1
1National Research Council, Ottawa ON, Canada
High harmonic generation in atoms andmolecules can be viewed as a time-reversed photoionization process. An
electron is removed fromthe parent by an intense femtosecond laser field. The electron is then driven back to the
parent ion by the same field within one optical cycle. The electron can recombine back to the ground state, and thereby
emit an XUV photon. The recombination dipolemoments are very similar to photoionization dipolemoments, and
contain information about the electronic structure of the parentmolecule. High harmonic spectroscopy has several
advantages over photoionization, such as the highly parallelmeasurement atmany photon energies simultaneously,
the ability tomeasure polarization and phase of the photons, the high time resolution, and the ability to align the
molecules in space. We apply high harmonic spectroscopy to study the unimolecular dissociation of the bromine
molecule. We show that the strong emission fromunexcitedmolecules acts as a local oscillator in a homodyne
detection scheme, and permits themeasurement of both amplitude and phase of the excited state emission. Using
a transient grating excitation geometry in bromine, we can follow the dissociatingmolecules along the reaction
coordinate. Because high harmonic spectroscopy is sensitive to the electronic state of amolecule, this technique
shows promise to observe changes in electronic structure during a chemical reaction, for example at conical
intersections.
4PL3(invited)

Femtosecond spin-orbit excitations in ferromagnets
H Dürr1
1PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, United States
Polarized soft X-rays have been used over the past 20 years to obtain fascinating new insights into nanoscale
magnetism. The separation of spin and orbitalmagneticmoments, for instance, enabled detailed insights into the
interplay of exchange and spin-orbit interactions at the atomic level. The now available polarized soft X-ray pulses
with only 100 fs duration allow us to observe themagnetic interactions at work in real time. The ultimate goal of such
studies is to understand how spinsmay bemanipulated by ultrashortmagnetic field, spin polarized current or light
pulses. In this talk I will focus on fs laser induced spin-orbit dynamics in 3d transitionmetals, 4f systems and their
alloys. Using fs X-ray pulses fromthe BESSY II femtoslicing facility I will show how fs excitation of the electronic system
modifies the spin-orbit interaction enabling ultrafast angularmomentum transfer between spin, orbital and lattice
degrees of freedom. An outlook will be given on how X-ray free electron laser radiation will revolutionize this field.

Core-electron tunneling in diatomics interacting with intense ultrashort-pulsed
XUV and X-ray radiation: theoretical studies
O Ponomarenko1,2
1ARC CoE CXS, The School of Physics, The University of Melbourne, Melbourne, Victoria, Australia; 2ARC CoE CXS, The School of Physics, The Monash University, Melbourne, Victoria,
Australia
New sources of intense XUV/X-ray ultra-short pulse radiation - X-ray free-electron and HHG lasers - present a unique opportunity to develop
time-resolved structure determination schemes. These techniques wouldmake it possible to trace the time evolution of the electronic density
inmolecular systems, and identify signatures of core-electron transitions during the probe pulse. The field of XFEL is sufficient to influence the
migration by field-induced bound-state tunnelling of core hole states generated by one-photon photoionization. Sincemolecular imaging experiments
at atomic resolution are sensitive to the core-electron density in the target, anymodification of this density has potential implications for the imaging
experiments using femtosecond X-ray pulses.In this presentation, we provide an illustration of the effects of field-induced core-hole transport on
X-ray scattering properties inmolecular systems. As an example, we consider inter-well tunneling of a core electronic density through the Coulomb
barrier between nuclei in a single-electron dicarbonmolecular ion driven by intense extreme-ultraviolet laser field. We employ a simple numerical
two-statemodel which is further elaborated and supported by a three-dimensionalmodel based on numerical solution of the time-dependent
Schrödinger equation. The laser field parameters determining core-hole tunneling rates are found to be scalable for the higher intensity/shorter
wavelength regimes. The implications of this study on the reconstruction ofmolecular structures by analysis of scattering data in single-shot X-ray
free-electron laser experiments are discussed.

Related products

Product Data Sheets

Del Mar Photonics Product brochures - Femtosecond products data sheets (zip file, 4.34 Mbytes) - Del Mar Photonics

Send us a request for standard or custom ultrafast (femtosecond) product

Pulse strecher/compressor
Avoca SPIDER system
Buccaneer femtosecond fiber lasers with SHG Second Harmonic Generator
Cannon Ultra-Broadband Light Source
Cortes Cr:Forsterite Regenerative Amplifier
Infrared cross-correlator CCIR-800
Cross-correlator Rincon
Femtosecond Autocorrelator IRA-3-10
Kirra Faraday Optical Isolators
Mavericks femtosecond Cr:Forsterite laser
OAFP optical attenuator
Pearls femtosecond fiber laser (Er-doped fiber, 1530-1565 nm)
Pismo pulse picker
Reef-M femtosecond scanning autocorrelator for microscopy
Reef-RTD scanning autocorrelator
Reef-SS single shot autocorrelator
Femtosecond Second Harmonic Generator
Spectrometer ASP-100M
Spectrometer ASP-150C
Spectrometer ASP-IR
Tamarack and Buccaneer femtosecond fiber lasers (Er-doped fiber, 1560+/- 10nm)
Teahupoo femtosecond Ti:Sapphire regenerative amplifier
Femtosecond third harmonic generator
Tourmaline femtosecond fiber laser (1054 nm)
Tourmaline TETA Yb femtosecond amplified laser system
Tourmaline Yb-SS femtosecond solid state laser system
Trestles CW Ti:Sapphire laser
Trestles femtosecond Ti:Sapphire laser
Trestles Finesse femtosecond lasers system integrated with DPSS pump laser
Wedge Ti:Sapphire multipass amplifier
Multi-terawatt lasers overview

complete conference program

Ultra-fast dynamics of spin and orbital magnetic moments by time resolved
XMCD.
C Boeglin,1 E Beaurepaire,1 V Halté,1 V Lopez-Flores,1 J Arabski,1 C Stamm,2 N Pontius,2 HA Dürr,2 JY Bigot1
1Institut de Physique et de Chimie de Strasbourg, UMR7504, CNRS et Université de Strasbourg, Strasbourg, France; 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH,
BESSY II, Berlin, Germany
Ultrafastmagnetization dynamics is an important issue for both fundamental science and for applications. Since the first observation of laser
induced spin dynamics, themechanisms of angularmomentum dissipation at picosecond timescales have been debated and in order to discuss
such microscopicmechanisms, it is desirable to quantitatively probe absolute values ofmagnetization with high temporal resolution. In this
context, we have used ultrashort optical laser pulses (60 fs duration) to induce changes of themagnetization in a ferromagnetic CoPd alloy film
with perpendicular anisotropy; the dynamics was probed with circularly polarized femtosecond X-ray pulses (100 fs duration),measuring the X-ray
magnetic circular dichroism (XMCD) at Co L2 and L3 edges. The use of sum rules of XMCD allows disentangling for the first time, the spin and orbital
components of themagneticmoment. We show that the dynamics of Lz and Sz are different, leading to a drop by ~30% of the ratio Lz / Sz about 500
fs after the absorption of the laser pulse. These signals will be compared to the purely electronic effect,measured by the intensity at L3 edge with
linearly polarized X-rays. Our results show that themechanism responsible for the ultrafast laser induced demagnetization requires the concept of
spin-orbit interaction, and that themagneto-crystalline anisotropy energy is an important quantity to consider

Dynamic investigation of photoinduced phase transition in Prussian blue
analogs by picosecond time-resolved XAFS
S Nozawa,1 T Sato,1 A Tomita,2 M Hoshino,2 H Tokoro,3 S I Ohkoshi,3 S Y Koshihara,2 S I Adachi1
1High Energy Accelerator Research Organization, Institute of Materials Structure Science, Tsukuba, Ibaraki, Japan; 2Department of Materials Science, Tokyo Institute of
Technology, Meguro-ku, Tokyo, Japan; 3Department of Chemistry, School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
Prussian blue analogs have recently attracted great interest due to their exotic natures such as photo-magnetization as well as photo-structural
change in the photoinduced phase transition (PIPT).1,2 The investigation of the dynamics of PIPT allows us to obtain information how the photoexcitation
in the single site expands into amacroscopic phase transition. Picosecond time-resolved XAFS experiments were performed on the NW14A
at the Photon Factory Advanced Ring (PF-AR).3,4 The time-resolved XAFS spectra were collected by the pump and probe technique combined with a
femtosecond laser system. In EXAFS and XANES regions, spin-lattice-charge coupled dynamics acompanied with the PIPT were obtained at 100 ps
resolution. The detailed results will be presented.
[1] Tokoro, H. et al., Appl. Phys. Lett., 2003, 82, 1245.
[2] Yamauchi, T. et al., Phys. Rev. B, 2005, 72, 214425.
[3] Nozawa, S. et al., J. Synchrotron Rad., 2007, 14, 313.
[4] Nozawa, S. et al., J. Am. Chem. Soc., 2010, 132, 61.

Excited-electron dynamics of bismuth film grown on Si (111) surface by
interferometric time-resolved two-photon photoelectron spectroscopy
S Fujimasa,1 M Imamura,2 H Yasuda3
1Department of Mechanical Engineering, Kobe University, Nada, Kobe, Japan; 2Synchrotron Light Application Center, Saga University, Saga, Saga, Japan; 3Research Center for
Ultra-High Voltage Electron Microscopy, Osaka University, Ibaraki, Osaka, Japan
Bismuth is a typical semi-metallic element and various studies on the relevant characteristic properties have been carried out for the purpose of
applications to electronic, optic andmagnetic devices. Fromviewpoints of device applications and fundamental physics, photo-excited electrons play
an important role in physical and chemical phenomena and it is necessary to understand the carrier dynamics. We have carried out a femtosecond
interferometric time-resolved two-photon photoemission (ITR-2PPE) study in order to investigate the excited electron dynamics on femtosecond
time-scale at excited states of bismuth film on Si (111) surface. Two kinds of crystalline bismuth films were prepared by vapor-deposition onto an
Si (111)7×7 clean surface (p-type 0.02Ωmwafer) using Knudsen-cell. On the single crystalline Bi (111) surface, all the energy relaxation time
of excited-electron is less than 15 fs in the energies (Ei) of the range from1.0 to 2.6 eV above Fermi energy, and decreases with increasing Ei.
This result indicates that this fast relaxation is induced by electron-electron scattering. The values of the energy relaxation timemeasured can be
described as a function of 9.15×Ei
-1.10. On the other hand, on the poly crystalline Bi surface, the values of the energy relaxation time by electronelectron
scattering are slightly larger than those on the single crystalline surface, and can be described as a function of 11.41×Ei
-0.75. Thatmeans the
electron-electron scattering rate of single crystalline bismuth surface is higher. It is suggested that the single crystalline bismuth surface has higher
densities of states near the Fermi surface than those of poly crystalline bismuth surface, since excited electron is necessary to scatter with valence
band electrons under the condition of both energy andmomentum conservation.

Terahertz-field driven streak-camera for single-shot measurements of the
temporal profile of XUV-pulses from FLASH
U Frühling,1 M Gensch,2 T Gebert,1 B Schütte,1 R Kalms,1 M Krikunova,1 E Ploenjes,3 M Drescher1
1Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany; 2Helmhotz-Zentrum Berlin, Berlin, Germany; 3Deutsches Elektronen-Synchrotron DESY, Hamburg,
Germany
The Free-Electron Laser in Hamburg (FLASH) delivers highly intense ultrashort XUV light pulses with pulse durations of a few femtoseconds. Due to
the stochastic nature of the light generation scheme based on self amplified spontaneous emission (SASE), the duration and temporal profile of the
XUV pulses fluctuate fromshot to shot. For a single shotmeasurement of the temporal profile a THz-field driven streak-camera has been developed.
In the experiment the XUV pulses are superimposed in a gas target with synchronized THz-pulses generated by the same electron bunch in a THzundulator
downstream of the SASE XUV-undulator. The XUV photons ionize the gas atoms and generate photoelectrons. These photoelectrons are
accelerated by the time-dependent electric field of the THz-light pulse, where themomentum gain depends on the THz electric field at the ionization
time. Bymeasuring the photoelectronmomenta we can therefore reconstruct the temporal profile of the ionizing XUV pulse. This technique is
intensively used in attosecondmetrology where near infrared streaking fields are employed. Here, it is adapted for the analysis of pulse durations in
the few femtosecond range by choosing a hundred times longer far infrared streaking wavelength.

complete program

Product Data Sheets

Del Mar Photonics Product brochures - Femtosecond products data sheets (zip file, 4.34 Mbytes) - Del Mar Photonics

Send us a request for standard or custom ultrafast (femtosecond) product

Pulse strecher/compressor
Avoca SPIDER system
Buccaneer femtosecond fiber lasers with SHG Second Harmonic Generator
Cannon Ultra-Broadband Light Source
Cortes Cr:Forsterite Regenerative Amplifier
Infrared cross-correlator CCIR-800
Cross-correlator Rincon
Femtosecond Autocorrelator IRA-3-10
Kirra Faraday Optical Isolators
Mavericks femtosecond Cr:Forsterite laser
OAFP optical attenuator
Pearls femtosecond fiber laser (Er-doped fiber, 1530-1565 nm)
Pismo pulse picker
Reef-M femtosecond scanning autocorrelator for microscopy
Reef-RTD scanning autocorrelator
Reef-SS single shot autocorrelator
Femtosecond Second Harmonic Generator
Spectrometer ASP-100M
Spectrometer ASP-150C
Spectrometer ASP-IR
Tamarack and Buccaneer femtosecond fiber lasers (Er-doped fiber, 1560+/- 10nm)
Teahupoo femtosecond Ti:Sapphire regenerative amplifier
Femtosecond third harmonic generator
Tourmaline femtosecond fiber laser (1054 nm)
Tourmaline TETA Yb femtosecond amplified laser system
Tourmaline Yb-SS femtosecond solid state laser system
Trestles CW Ti:Sapphire laser
Trestles femtosecond Ti:Sapphire laser
Trestles Finesse femtosecond lasers system integrated with DPSS pump laser
Wedge Ti:Sapphire multipass amplifier
Multi-terawatt lasers overview

complete conference program