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The KMC-3 XPP endstation of the synchrotron BESSY II is dedicated to time-resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X-ray diffraction with an accessible time range from 17 ps to several microseconds., The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the ‘low-α’ operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.

International audience; When the spatial dimensions of metallic heterostructures shrink below the mean free path of its conduction electrons, the transport of electrons and hence the transport of thermal energy by electrons continuously changes from diffusive to ballistic. Electron-phonon coupling sets the mean free path to the nanoscale and the time for equilibration of electron and lattice temperatures to the picosecond range. A particularly intriguing situation occurs in trilayer heterostructures combining metals with very different electron-phonon coupling strength: Heat energy deposited in few atomic layers of Pt is transported into a nanometric Ni film, which is heated more than the Cu film through which the heat is released. Femtosecond pump-probe experiments with hard X-ray pulses provide a layer-specific probe of the heat energy. A purely diffusive two-temperature model with increased thermal conductivity of hot electrons excellently reproduces the observed signals from all three layers. At the time when the Ni lattice is maximally heated, no significant heat has entered the Cu lattice. This phenomenon would be enhanced in thinner layers where ballistic transport dominates. In this context it is shown that purely diffusive transport can lead to a linear time-to-length dependence that must not be misinterpreted as ballistic transport.

Ultrafast X-ray diffraction experiments require careful adjustment of the spatial overlap between the optical excitation and the X-ray probe pulse. This is especially challenging at high laser repetition rates. Sample distortions caused by the large heat load on the sample and the relatively low optical energy per pulse lead to only tiny signal changes. In consequence, this results in small footprints of the optical excitation on the sample, which turns the adjustment of the overlap difficult. Here a method for reliable overlap adjustment based on reciprocal space mapping of a laser excited thin film is presented.

We use broadband time domain Brillouin scattering to observe coherently generated phonon modes in bulk and nanolayered samples. We transform the measured transients into a frequency-wavevector diagram and compare the resulting dispersion relations to calculations. The detected oscillation amplitude depends on the occupation of phonon modes induced by the pump pulse. For nanolayered samples with an appropriately large period, the whole wavevector range of the Brillouin zone becomes observable by broadband optical light scattering. The backfolded modes vanish, when the excitation has passed the nanolayers and propagates through the substrate underneath.

We present time-resolved x-ray reflectivity measurements on laser excited coherent and incoherent surface deformations of thin metallic films. Based on a kinematical diffraction model, we derive the surface amplitude from the diffracted x-ray intensity and resolve transient surface excursions with sub-Angstrom spatial precision and 70 ps temporal resolution. The novel analysis allows for decomposition of the surface amplitude into multiple coherent acoustic modes and a substantial contribution from incoherent phonons which constitute the sample heating., Comment: 4 pages, 3 figures

The amplitude of surface distortions induced by transient grating excitation has been measured via time-dependent x-ray diffraction (XRD). Results show 4 times higher amplitude of the incoherent surface deformation compared to the propagating surface acoustic waves with a total amplitude of 4a.

Wavevector-selective impulsive excitation of phonon-polaritons by a spectrally broad femtosecond transient grating produces wavepackets propagating in opposite directions. The photons in spectrally narrow probe pulses are scattered from these elementary excitations in lithium niobate (LiNbO3). Both elastically and inelastically scattered photons are simultaneously detected in a spectrometer. The Stokes- and anti-Stokes shifted probe pulses uniquely determine the propagation direction of the detected polariton wavepacket components and correspond to creation or annihilation of phonon-polaritons. Our experiments with spectrally broad pump and spectrally narrow probe pulses allows dissecting the four-wave-mixing process into two sequential stimulated Raman scattering events.

A diffractometer setup is presented, based on a laser-driven plasma X-ray source for reciprocal-space mapping with femtosecond temporal resolution. In order to map out the reciprocal space, an X-ray optic with a convergent beam is used with an X-ray area detector to detect symmetrically and asymmetrically diffracted X-ray photons simultaneously. The setup is particularly suited for measuring thin films or imperfect bulk samples with broad rocking curves. For quasi-perfect crystalline samples with insignificant in-plane Bragg peak broadening, the measured reciprocal-space maps can be corrected for the known resolution function of the diffractometer in order to achieve high-resolution rocking curves with improved data quality. In this case, the resolution of the diffractometer is not limited by the convergence of the incoming X-ray beam but is solely determined by its energy bandwidth.

We introduce a method to analyze optical and viscoelastic properties of the surrounding medium of GNRs by using hyper-sound waves, generated by new, efficient, inexpensive optoacoustic soft-matter transducers.

International audience; We study the vibrations of ultrathin gold nanotriangles upon optical excitation of the electron gas by ultrafast X-ray diffraction. We quantitatively measure the strain evolution in these highly asymmetric nano-objects, providing a direct estimation of the amplitude and phase of the excited vibrational motion. The maximal strain value is well reproduced by calculations addressing pump absorption by the nanotriangles and their resulting thermal expansion. The amplitude and phase of the out-of-plane vibration mode with 3.6 ps period dominating the observed oscillations are related to two distinct excitation mechanisms. Electronic and phonon pressures impose stresses with different time dependences. The nanosecond relaxation of the expansion yields a direct temperature sensing of the nano-object. The presence of a thin organic molecular layer at the nanotriangle/substrate interfaces drastically reduces the thermal conductance to the substrate.

We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain epsilon similar to 5 x 10(-4) is calibrated by ultrafast X-ray diffraction.

We present a nanostructured device that functions as photoacoustic hard x-ray switch. The device is triggered by femtosecond laser pulses and allows for temporal gating of hard x-rays on picosecond (ps) timescales. It may be used for pulse picking or even pulse shortening in 3rd generation synchrotron sources. Previous approaches mainly suffered from insufficient switching contrasts due to excitation-induced thermal distortions. We present a new approach where thermal distortions are spatially separated from the functional switching layers in the structure. Our measurements yield a switching contrast of 14, which is sufficient for efficient hard x-ray pulse shortening. The optimized structure also allows for utilizing the switch at high repetition rates of up to 208 kHz. Published by AIP Publishing.

Femtosecond X-ray scattering offers the opportunity to investigate reversible lattice dynamics with unprecedented accuracy. We show in a prototype experiment how strain propagation modifies the functionality of a ferroelectric system on its intrinsic time scale.

We report on a versatile and accurate method for determining the time delay between femtosecond X-ray and optical pulses in an optical pump/X-ray diffraction probe experiment. Upon excitation with moderate pump fluences, Bragg peaks of thin SrTiO3 (STO)/SrRuO3 (SRO) superlattices display 50% changes in diffracted X-ray intensity, followed by a pronounced lineshift (Δθ/θ=0.03°) on a 10 ps time-scale. A parallel time-resolved measurement of the instantaneous all-optical reflectivity change allows for a precise temporal analysis of the fully reversible X-ray response and gives the time delay zero with an accuracy of ±100 fs.

The plasmon resonance of metal nanoparticles determines their optical response in the visible spectral range. Many details such as the electronic properties of gold near the particle surface and the local environment of the particles influence the spectra. We show how the cheap but highly precise fabrication of composite nanolayers by spin-assisted layer-by-layer deposition of polyelectrolytes can be used to investigate the spectral response of gold nanospheres (GNS) and gold nanorods (GNR) in a self-consistent way, using the established Maxwell–Garnett effective medium (MGEM) theory beyond the limit of homogeneous media. We show that the dielectric function of gold nanoparticles differs from the bulk value and experimentally characterize the shape and the surrounding of the particles thoroughly by SEM, AFM and ellipsometry. Averaging the dielectric functions of the layered surrounding by an appropriate weighting with the electric field intensity yields excellent agreement for the spectra of several nanoparticles and nanorods with various cover-layer thicknesses.

Coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were measured nondestructively with sub-picometer spatial and sub-picosecond time resolution via ultrafast X-ray diffraction (XRD). The femtosecond excitation of a GaAs/AlGaAs superlattice with 1.5 eV photons results in spatially periodic stress, which induces a coherent ZFLAP with a 3.5 ps period. The motion is directly monitored by femtosecond X-ray pulses at a kilohertz repetition rate. The intensity change AR/R = 0.03 of the -1 st order satellite peak of the (002) reflection of bulk AlGaAs is directly proportional to the induced lattice strain of Δa/a 0 =1.5×10 -4 . The phase and amplitude of the oscillatory XRD signal around a new equilibrium demonstrates the displacive excitation of coherent phonons (DECP) as the dominant mechanism for strong excitation. We discuss different mechanisms which account for impulsive stress, and argue that the electronic stress due to the deformation potential dominates.

X-ray diffraction with femtosecond time-resolution represents a direct probe of ultrafast structural changes in condensed matter. The generation of ultrashort X-ray pulses in laser-driven plasma and/or accelerator-based sources has made substantial progress, and has allowed for studies of transient structures with an unprecedented accuracy. Herein, recent work on transient crystalline structures is reviewed, with the focus on laser-based experiments.

We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, using a tabletop femtosecond laser-based plasma source. We demonstrate a 23 µm focus with a toroidally bent Ge single crystal. A maximum flux of 7 × 10 8 photons/(s mm 2 ) is generated in a 32 µm focus using a multi-layer mirror. An elliptical glass capillary yields the highest number of photons per Bragg angle (2 × 10 5 photons/(s mrad)). The largest number of photons (3 × 10 6 photons/s) per second is obtained in the 105 µm focus of a poly-capillary optical lens system. All numbers are given for characteristic Cu Kα photons.

The UDKM1DSIM toolbox is a collection of MATLAB (MathWorks Inc.) classes and routines to simulate the structural dynamics and the according X-ray diffraction response in one-dimensional crystalline sample structures upon an arbitrary time-dependent external stimulus, e.g. an ultrashort laser pulse. The toolbox provides the capabilities to define arbitrary layered structures on the atomic level including a rich database of corresponding element-specific physical properties. The excitation of ultrafast dynamics is represented by an N-temperature model which is commonly applied for ultrafast optical excitations. Structural dynamics due to thermal stress are calculated by a linear-chain model of masses and springs. The resulting X-ray diffraction response is computed by dynamical X-ray theory. The UDKM1DSIM toolbox is highly modular and allows for introducing user-defined results at any step in the simulation procedure. Program summary Program title: udkm1Dsim Catalogue identifier: AERH_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AERH_v1_0.html Licensing provisions: BSD No. of lines in distributed program, including test data, etc.: 130221 No. of bytes in distributed program, including test data, etc.: 2746036 Distribution format: tar.gz Programming language: Matlab (MathWorks Inc.). Computer: PC/Workstation. Operating system: Running Matlab installation required (tested on MS Win XP -7, Ubuntu Linux 11.04-13.04). Has the code been vectorized or parallelized?: Parallelization for dynamical XRD computations. Number of processors used: 1-12 for Matlab Parallel Computing Toolbox; 1 - infinity for Matlab Distributed Computing Toolbox External routines: Optional: Matlab Parallel Computing Toolbox, Matlab Distributed Computing Toolbox Required (included in the package): mtimesx Fast Matrix Multiply for Matlab by James Tursa, xml io tools by Jaroslaw Tuszynski, textprogressbar by Paul Proteus Nature of problem: Simulate the lattice dynamics of 1D crystalline sample structures due to an ultrafast excitation including thermal transport and compute the corresponding transient X-ray diffraction pattern. Solution method: Restrictions: The program is restricted to 1D sample structures and is further limited to longitudinal acoustic phonon modes and symmetrical X-ray diffraction geometries. Unusual features: The program is highly modular and allows the inclusion of user-defined inputs at any time of the simulation procedure. Running time: The running time is highly dependent on the number of unit cells in the sample structure and other simulation parameters such as time span or angular grid for X-ray diffraction computations. However, the example files are computed in approx. 1-5 min each on a 8 Core Processor with 16 GB RAM available.

We demonstrate a sub-picosecond 1-kHz femtosecond X-ray source with a well accessible quasi-point size (10 μm diameter) providing Cu, Ni and Ti K α emission with a maximum flux up to 7.0 x 10 6 phot/srad/pulse in continuous operation. A new geometry, which essentially facilitates the adjustment of time-resolved measurements and diminishes the temporal jitter between the X-ray probe and the laser pump pulse is implemented. An upper limit of 500 fs was measured for the duration of the X-ray pulses.

A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of

We investigate coherent phonon propagation in a thin film of ferroelectric PbZr0.2Ti0.8O3 (PZT) by ultrafast x-ray diffraction (UXRD) experiments, which are analyzed as time-resolved reciprocal space mapping (RSM) in order to observe the in- and out-of-plane structural dynamics simultaneously. The mosaic structure of the PZT leads to a coupling of the excited out-of-plane expansion to in-plane lattice dynamics on a picosecond timescale, which is not observed for out-of-plane compression., 5 pages, 4 figures

Reversible structural changes of a nanostructure were measured nondestructively with subpicometer spatial and subpicosecond temporal resolution via x-ray diffraction (XRD). The spatially periodic femtosecond excitation of a gallium arsenide/aluminum gallium arsenide superlattice results in coherent lattice motions with a 3.5-picosecond period, which was directly monitored by femtosecond x-ray pulses at a 1-kilohertz repetition rate. Small changes (Δ R / R = 0.01) of weak Bragg reflexes ( R = 0.005) were detected. The phase and amplitude of the oscillatory XRD signal around a new equilibrium demonstrate that displacive excitation of the zone-folded acoustic phonons is the dominant mechanism for strong excitation.

When gold nanoparticles are covered with nanometric layers of transparent polyelectrolytes, the plasmon absorption spectrum A(λ) increases by a factor of approximately three and shifts to the red. These modifications of dissipative experimental observables stop when the cover layer thickness approaches the particle diameter. Spectral modifications of dispersive parameters like the reflection R, however, keep changing with increasing cover layer thickness. The shift of the plasmon resonance caused by two interacting particle layers is studied as a function of the separating distance between the two layers. We discuss these observations in the context of an effective medium theory and conclude that it can only be applied for a layer thickness on the order of the particle diameter.

We show ultrafast all-optical reflectivity measurements on nonlinear propagating strain pulses for different fluences calibrated by ultrafast X-ray diffraction (UXRD) to the corresponding induced strain amplitudes.

We present an experimental setup of a laser-driven x-ray plasma source for femtosecond x-ray diffraction. Different normalization schemes accounting for x-ray source intensity fluctuations are discussed in detail. We apply these schemes to measure the temporal evolution of Bragg peak intensities of perovskite superlattices after ultrafast laser excitation.

We present time-resolved XRD experiments which evidence the generation of a tunable high-frequency monochromatic phonon wavepacket by multiple optical excitation of a thin film transducer. The decay time of these phonon pulses is ~ 140 ps.

We present first results on mosaicity changes in a ferroelectric PbZr0.2Ti0.8O3 thin film on a ps timescale utilizing a new ultrafast reciprocal space mapping technique.

A 100 ps synchrotron pulse of hard X-rays is shorted to few picoseconds by exploiting coherent phonon dynamics in a thin metallic SrRuO 3 layer. A first pump-probe experiment with the shortened X-ray pulse is presented.

We determined experimentally the complex transient optical dielectric function of a well-characterized polyelectrolyte/gold-nanoparticle composite system over a broad spectral range upon short pulse laser excitation by simultaneously measuring the time-dependent reflectance and transmittance of white light pulses with femtosecond pump-probe spectroscopy. We extracted directly the ultrafast changes in the real and imaginary parts of the effective dielectric function, epsilon(eff)(r) (omega,t)and epsilon(eff)(i) (omega,t), from the experiment. This complete experimental set of information on the time-dependent complex dielectric function challenges theories modeling the transient dielectric function of gold particles and the effective medium.

Ultrafast x-ray dir action (UXRD) has become more and more prevalent in various scienti“c disciplines that areinterested in directly observing atomic motion in real time. The timescale, amplitude and phase of collectiveatomic motion can be determined with high accuracy, even when the induced amplitude is smaller than thermal”uctuations. The structural rearrangements induced by an ultrafast stimulus (charge carriers excitation or heatdeposition by a laser pulse) can be recorded in real time. Here we report on a new laser-driven plasma-x-raysource (PXS) and discuss dierent applications which will be addressed in UXRD experiments.Keywords: ultrafast x-ray dir action 1. INTRODUCTION Probing atomic motions in condensed matter on the fs-timescale enables the investigation of various physicaleects which are directly linked to the atomic structure. Ultrafast x-ray dir action (UXRD) is capable ofmonitoring such dynamics with a sub-picometer spatial and sub-picosecond temporal resolution.

Ultrafast X-ray diffraction yields material-specific information on transient strain in crystals, thin films and multilayers. Here we highlight ultrafast heat-driven processes in ferroelectric and ferromagnetic oxides.

We investigated the generation and propagation of coherent phonons in an oxide superlattice of SrRuO3and SrTiO3. The rich dynamics resulted in drastic modulations of various Bragg peaks on a 1-ps timescale.

We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.

Femtosecond optical excitation of magnetically ordered SrRuO3 nanolayers leads to an ultrafast demagnetization and a concomitant magnetoelastic contractive stress. The resulting ultrafast structural response of the sample is imaged by femtosecond X-ray diffraction.

Laser-driven plasma sources of femtosecond hard X-ray pulses have found widespread application in ultrafast X- ray diffraction. The recent development of plasma sources working at kilohertz repetition rates has allowed for diffraction experiments with strongly improved sensitivity, now revealing subtle fully reversible changes of the geometry of crystal lattices. We provide a brief review of this development and present a novel plasma source with an optimized mechanical and optical design, providing a high flux of several 10(10) photons/s at the Cu-K alpha energy of 8.04 keV and a pulse duration of a parts per thousand currency sign300 fs. First experiments, including the generation of Debye-Scherrer diffraction patterns from Si powder, demonstrate the high performance of this source.

We report the first analysis of the polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system by femtosecond x-ray diffraction. Two Bragg reflections provide information on the coupled dynamics of the two relevant phonon modes for ferroelectricity in perovskites, the tetragonal distortion and the soft mode. Optical excitation of the ${\mathrm{SrRuO}}_{3}$ metal layers generates giant stress ($g1\text{ }\text{ }\mathrm{GPa}$) compressing the ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}$ layers by up to 2%. The resulting change of tetragonality reaches a maximum after 1.3 ps. As a result, the ferroelectric polarization $P$ is reduced by up to 100% with a slight delay that is due to the anharmonic coupling of the two modes.

We demostrate a sub-picosecond 1-kHz femtosecond X-ray source (flux: 5times1010 photons/s) with a well accessible quasi-point size (10 mum diameter) providing Cu Kalpha emission in continuous operation (10 hours), which we use to characterize two different types of focusing optics

For the first time femtosecond X-ray diffraction measures the coherent strain connected to a zone-folded longitudinal acoustic phonon optically excited in a GaAs/AlGaAs superlattice, giving direct evidence for the displacive excitation mechanism.

We monitor how destructive interference of undesired phonon frequency components shapes a quasi-monochromatic hypersound wavepacket spectrum during its local real-time preparation by a nanometric transducer and follow the subsequent decay by nonlinear coupling. We prove each frequency component of an optical supercontinuum probe to be sensitive to one particular phonon wavevector in bulk material and cross-check this by ultrafast x-ray diffraction experiments with direct access to the lattice dynamics. Establishing reliable experimental techniques with direct access to the transient spectrum of the excitation is crucial for the interpretation in strongly nonlinear regimes, such as soliton formation.

We present a setup for ultrafast x-ray diffraction (UXRD) based at the storage ring BESSY II, in particular, a pump laser that excites the sample using 250 fs laser-pulses at repetition rates ranging from 208 kHz to 1.25 MHz. We discuss issues connected to the high heat-load and spatio-temporal alignment strategies in the context of a UXRD experiment at high repetition rates. The spatial overlap between laser pump and x-ray probe pulse is obtained with 10 mu m precision and transient lattice changes can be recorded with an accuracy of delta a/a(0) = 10(-6). We also compare time-resolved x-ray diffraction signals from a laser excited LSMO/STO superlattice with phonon dynamics simulations. From the analysis we determine the x-ray pulse duration to 120 ps in standard operation mode and below 10 ps in low-alpha mode.

We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory.

We implemented an experimental scheme for ultrafast x-ray diffraction at storage rings based on a laser-driven Bragg-switch that shortens the x-ray pulses emitted from an undulator. The increased time-resolution is demonstrated by observing changes of intensity, position and width of the diffraction peaks of a La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice sample after optical excitation, i.e., by quantitatively measuring the propagation of an expansion wave through the sample. These experimental transients with timescales of 35 to 60 ps evidence a reduction of the x-ray pulse duration by a factor of two.

We experimentally demonstrate efficient switching of the hard x-ray Bragg reflectivity of a SrRuO3 /SrTiO3 superlattice by optical excitation of large-amplitude coherent acoustic superlattice phonons. The rocking curve changes drastically on a 1 ps timescale. The (0 0 116) reflection is almost extinguished (Delta R/R-0=-0.91), while the (0 0 118) reflection increases by more than an order of magnitude (Delta R/R-0=24.1). The change of the x-ray structure factor depends nonlinearly on the phonon amplitude, allowing manipulation of the x-ray response on a timescale considerably shorter than the phonon period. Numerical simulations for a superlattice with slightly changed geometry and realistic parameters predict a switching-contrast ratio Delta R/R-0 of 700 with high reflectivity. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3402773]

Electronic and vibrational coherences in the B 3Π(0+u) ← X1Σ+g transition of chlorine (Cl2) molecules doped in an argon matrix are investigated by exciting with a pulse pair whose relative phase is scanned for every time delay step. The spacing and position of the generated spectral comb are controlled by the delay and relative phase of the pulses. The B 3Π(0+u) ← X1Σ+g excitation spectrum shows a progression of zero phonon lines which are decoupled from the lattice and of phonon side bands which originate from a concerted excitation of intramolecular and lattice vibrations. The molecular anharmonicity is compensated for by applying a negative chirp difference of the two pulses, which leads to an asymmetry in the signal around time zero. Absolute phase values are determined from spectral positions in the measured comb patterns. They are used to calculate fringe patterns and to simulate interferograms by a multiplication with the excitation spectrum which are compared with the measured ones in detail. From simulated interferograms of zero phonon lines and phonon side bands, we show that the two contributions can be selected with a large contrast by a time delay of two molecular vibrational periods.

We demonstrate a subpicosecond 1 kHz femtosecond x-ray source with a well-accessible quasi-point size (10??m diameter) providing Cu K? emission with a maximum flux of 6.8×1010? photons?s for continuous operation of 10 h. A new geometry that essentially facilitates the adjustment and diminishes the temporal jitter between the x-ray probe and the laser pump pulse is implemented for time-resolved diffraction experiments.

We demonstrate a concept for short x-ray generation at 1kHz repetition rate from a thin-foil target in a very compact configuration, which allows one, essentially, to decrease the distance between x-ray source and investigated object. The scaling for the hard x-ray yield and the hot electron temperature with the pulse intensity are determined and best described by a power law. The useful photon fluxes of 3.4×109 and 3.3×109phot∕(ssrad) are generated for the Ni- and Cu Kα lines, respectively. The size of the x-ray source was detected to be 10μm.

Electronic and vibrational coherences of Cl2 embedded in solid Ar are investigated by exciting to the B state with a phase-locked pulse pair from an unbalanced Michelson interferometer, where the chirp difference matches the B state anharmonicity. Recording the A′ → X fluorescence after relaxation is compared to probing to charge transfer states by a third pulse. The three-pulse experiment delivers more details on the decoherence processes. The signal modulation due to phase tuning up to the third vibrational round-trip time indicates that the electronic coherence in the B ← X transition is preserved for more than 660 fs in the solid Ar environment where many body electronic interactions take place. Vibrational coherence lasts longer than 3 ps according to the observed half revival of the wavepacket. Control of the coupling between wavepacket motion and lattice oscillation is demonstrated by tuning the relative phase between the phase-locked pulses, preparing wavepackets predominantly composed of either zero-phonon lines or phonon side bands.

The polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system is studied by femtosecond x-ray diffraction. Two Bragg reflections provide information on the coupled dynamics of the two relevant phonon modes for ferroelectricity in perovskites, the tetragonal distortion and the ion displacement. Optical excitation of the metallic SrRuO3(SRO) layers generates giant stress, compressing the ferroelectric PbTr0.2Ti0.8O3(PZT) layers by up to 2%. The maximum elongation of the tetragonal mode is reached after 1.3 ps. With a slight delay the ferroelectric polarization P is reduced by up to 100 percent that is due to the anharmonic coupling of the two modes.