Frequency-domain interferometry for the determination of time delay between two extreme-ultraviolet wave packets generated by a tandem undulator.

Synchrotron radiation, emitted by relativistic electrons traveling in a magnetic field, has poor temporal coherence. However, recent research has proved that time-domain interferometry experiments, which were thought to be enabled by only lasers of excellent temporal coherence, can be implemented with synchrotron radiation using a tandem undulator. The radiation generated by the tandem undulator comprises pairs of light wave packets, and the longitudinal coherence within a light wave packet pair is used to achieve time-domain interferometry. The time delay between two light wave packets, formed by a chicane for the electron trajectory, can be adjusted in the femtosecond range by a standard synchrotron technology. In this study, we show that frequency-domain spectra of the tandem undulator radiation exhibit fringe structures from which the time delay between a light wave packet pair can be determined with accuracy on the order of attoseconds. The feasibility and limitations of the frequency-domain interferometric determination of the time delay are examined.

Time domain double slit interference of electron produced by XUV synchrotron radiation.

We present a new realization of the time-domain double-slit experiment with photoelectrons, demonstrating that spontaneous radiation from a bunch of relativistic electrons can be used to control the quantum interference of single-particles. The double-slit arrangement is realized by a pair of light wave packets with attosecond-controlled spacing, which is naturally included in the spontaneous radiation from two undulators in series. Photoelectrons emitted from helium atoms are observed in the energy-domain under the condition of detecting them one by one, and the stochastic buildup of the quantum interference pattern on a detector plane is recorded.

Double-pulsed wave packets in spontaneous radiation from a tandem undulator.

We verify that each wave packet of spontaneous radiation from two undulators placed in series has a double-pulsed temporal profile with pulse spacing which can be controlled at the attosecond level. Using a Mach-Zehnder interferometer operating at ultraviolet wavelengths, we obtain the autocorrelation trace for the spontaneous radiation from the tandem undulator. The results clearly show that the wave packet has a double-pulsed structure, consisting of a pair of 10-cycle oscillations with a variable separation. We also report the characterization of the time delay between the double-pulsed components in different wavelength regimes. The excellent agreement between the independent measurements confirms that a tandem undulator can be used to produce double-pulsed wave packets at arbitrary wavelength.

Electron Wave Packet Interference in Atomic Inner-Shell Excitation.

We report the observation of quantum interference between electron wave packets launched from the inner-shell 4d orbital of the Xe atom. Using pairs of femtosecond radiation wave packets from a synchrotron light source, we obtain time-domain interferograms for the inner-shell excitations. This approach enables the experimental verification and control of the quantum interference between the electron wave packets. Furthermore, the femtosecond Auger decay of the inner-shell excited state is tracked. To the best of our knowledge, this is the first observation of wave packet interference in an atomic inner-shell process, and also the first time-resolved experiment on few-femtosecond Auger decay using a synchrotron light source.

Controlling the Orbital Alignment in Atoms Using Cross-Circularly Polarized Extreme Ultraviolet Wave Packets.

We report on the use of pairs of 10-cycle extreme ultraviolet wave packets with attosecond-controlled spacing emitted by individual relativistic electrons within an electron bunch passing through a tandem undulator. Based on the temporal coherent control technique with circular polarization, we succeeded in controlling the excited state alignment in the photoexcitation of helium atoms, which we verified through the observation of oscillation in fluorescence yield depending on the attosecond-controlled delay time. Our work demonstrates the potential of undulator radiation for the generation of longitudinally coherent wave packets suitable for attosecond coherent control, an application which has hitherto been hidden in the incoherent nature of the radiation pulse emitted by a bunch of electrons.

Coherent control in the extreme ultraviolet and attosecond regime by synchrotron radiation.

Quantum manipulation of populations and pathways in matter by light pulses, so-called coherent control, is currently one of the hottest research areas in optical physics and photochemistry. The forefront of coherent control research is moving rapidly into the regime of extreme ultraviolet wavelength and attosecond temporal resolution. This advance has been enabled by the development of high harmonic generation light sources driven by intense femtosecond laser pulses and by the advent of seeded free electron laser sources. Synchrotron radiation, which is usually illustrated as being of poor temporal coherence, hitherto has not been considered as a tool for coherent control. Here we show an approach based on synchrotron radiation to study coherent control in the extreme ultraviolet and attosecond regime. We demonstrate this capability by achieving wave-packet interferometry on Rydberg wave packets generated in helium atoms.

Different Time Scales in the Dissociation Dynamics of Core-Excited CF_{4} by Two Internal Clocks.

Fragmentation processes following C 1s→lowest unoccupied molecular orbital core excitations in CF_{4} have been analyzed on the ground of the angular distribution of the CF_{3}^{+} emitted fragments by means of Auger electron-photoion coincidences. Different time scales have been enlightened, which correspond to either ultrafast fragmentation, on the few-femtosecond scale, where the molecule has no time to rotate and the fragments are emitted according to the maintained orientation of the core-excited species, or dissociation after resonant Auger decay, where the molecule still keeps some memory of the excitation process before reassuming random orientation. Potential energy surfaces of the ground, core-excited, and final states have been calculated at the ab initio level, which show the dissociative nature of the neutral excited state, leading to ultrafast dissociation, as well as the also dissociative nature of some of the final ionic states reached after resonant Auger decay, yielding the same fragments on a much longer time scale.

Stability and dissociation dynamics of N2 (++) ions following core ionization studied by an Auger-electron-photoion coincidence method.

An Auger-electron-photoion coincidence (AEPICO) method has been applied to study the stability and dissociation dynamics of dicationic states after the N K-shell photoionization of nitrogen molecules. From time-of-flight and kinetic energy analyses of the product ions, we have obtained coincident Auger spectra associated with metastable states of N2 (++) ions and dissociative states leading to N2 (++) → N(+) + N(+) and N(++) + N. To investigate the production of dissociative states, we present two-dimensional AEPICO maps which reveal the correlations between the binding energies of the Auger final states and the ion kinetic energy release. These correlations have been used to determine the dissociation limits of individual Auger final states.

Ultrafast dynamics in C 1s core-excited CF4 revealed by two-dimensional resonant Auger spectroscopy.

Following core excitation in an isolated molecule, ultrafast dissociation of one particular chemical bond can occur, where "ultrafast" is defined as taking place during the lifetime of the core hole, of the order of few femtoseconds. The signature of such phenomenon can be observed in resonant Auger spectra following core excitation. We present here an investigation of ultrafast dissociation following C 1s-to-σ* core excitation in CF4, with high-resolution resonant Auger spectroscopy. We are able to characterize final states of both the molecular ion and the CF3 (+) fragment. We use two-dimensional (2D) maps to record resonant Auger spectra across the resonance as a function of photon energy and to characterize ultrafast dynamics. This method provides immediate visual evidence of one of the important characteristics of the study of spectral features related to molecular versus fragment ionic final states, and namely their dispersion law. In the 2D maps we are also able to identify the dissociation limit for one of the molecular final states.

Single photon K(-2) and K(-1)K(-1) double core ionization in C(2)H(2n) (n=1-3), CO, and N(2) as a potential new tool for chemical analysis.

We have observed single photon double K-shell photoionization in the C(2)H(2n) (n=1-3) hydrocarbon sequence and in N(2) and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K(-2) process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K(-1)K(-1) process). In the C(2)H(2n) sequence, the spectroscopy of K(-1)K(-1) states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K(-1)K(-1) double core ionization in the C(2)H(2n) sequence and in the isoelectronic C(2)H(2n), N(2) and CO molecules validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

A local chemical environment effect in site-specific Auger spectra of ethyl trifluoroacetate.

We have investigated a local chemical environment effect on Auger spectra of ethyl trifluoroacetate (C(4)H(5)F(3)O(2)), using multi-electron coincidence spectroscopy and high-resolution electron spectroscopy. Site-specific KVV Auger spectra for each carbon atom, and for the fluorine and oxygen atoms are presented. The extent of hole localization in the final dicationic states was investigated with the help of theoretical calculations based on a two-hole population analysis. The Auger spectra have been simulated using a statistical approach. It is found that all Auger decays populate mainly localized dicationic states, with the two holes located either on the same fluorine atom or on adjacent fluorine atoms. While the decay of the F 1s hole populates exclusively the former states, the latter class of states is also populated by the decay of the C and O 1s holes.

Evidence of single-photon two-site core double ionization of C2H2 molecules.

We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 ± 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

Second-order autocorrelation of XUV FEL pulses via time resolved two-photon single ionization of He.

Second-order autocorrelation spectra of XUV free-electron laser pulses from the Spring-8 Compact SASE Source (SCSS) have been recorded by time and momentum resolved detection of two-photon single ionization of He at 20.45 eV using a split-mirror delay-stage in combination with high-resolution recoil-ion momentum spectroscopy (COLTRIMS). From the autocorrelation trace we extract a coherence time of 8 ± 2 fs and a mean pulse duration of 28 ± 5 fs, much shorter than estimations based on electron bunch-length measurements. Simulations within the partial coherence model [Opt. Lett. 35, 3441 (2010)] are in agreement with experiment if a pulse-front tilt across the FEL beam diameter is taken into account that leads to a temporal shift of about 6 fs between both pulse replicas.

Three-electron interatomic Coulombic decay from the inner-valence double-vacancy states in NeAr.

We have unambiguously identified interatomic Coulombic decay in NeAr from the inner-valence double-vacancy state Ne-Ar(2+)(3s(-2)) to outer-valence triple-vacancy states Ne(+)(2p(-1))-Ar(2+)(3p(-2)) by momentum-resolved electron-ion multicoincidence. This is the first observation of interatomic Coulombic decay where three electrons (3e) participate. The results suggest that this 3e interatomic Coulombic decay is significantly faster than other competing processes like fluorescence decay and charge transfer via curve crossing.

Ion-ion coincidence studies on multiple ionizations of N(2) and O(2) molecules irradiated by extreme ultraviolet free-electron laser pulses.

We have investigated multiple ionization of N(2) and O(2) molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility SCSS in Japan. Coulomb break-up of parent ions with charge states up to 5+ is found by the ion-ion coincidence technique. The charge-state dependence of kinetic energy release distributions suggests that the electrons are emitted sequentially in competition with the elongation of the bond length.

Three-dimensional visualization of renal artery stenosis by 64-channel multiple detector-row computed tomographical angiography: review of two paediatric cases.

UNLABELLED: Three-dimensional visualization of renal arteries has recently been established by helical contrast-enhanced multiple detector-row computed tomographical angiography (MDCTA) in adults. So far, no information is available on its use in children. We reported two children with renal artery stenosis detected by 64-channel MDCTA. The first patient probably had fibromuscular dysplasia and the other neurofibromatosis type 1. The technique showed a left renal artery stenosis with a small left kidney in the first patient and a right renal artery stenosis in the second. CONCLUSION: MDCTA is an accurate and noninvasive imaging technique, easily performed in children, and can be used as an alternative diagnostic modality in children with suspected renovascular hypertension.

Dissociation dynamics of C(6)H(6) and C(6)H(5)F molecules following carbon 1s and fluorine 1s photoionization studied by three-dimensional momentum imaging method.

Benzene and fluorobenzene molecules were multiply ionized through Auger decay following from the C 1s or the F 1s photoionization and their subsequent dissociations were studied utilizing position-sensitive time-of-flight measurements. The angular correlation between the momenta of (H(+)-H(+)) and (H(+)-F(+)) fragment ions derived from the multiply ionized benzene or fluorobenzene clearly reflects the hexagonal structure of the parent molecules, though the dissociations are not described by the simple Coulomb explosion model. Also, analysis on the planarity between the momentum of H(+), C(+), and F(+) reveals that these three ions are emitted almost in a single plane.

Cold-target recoil-ion momentum spectroscopy for diagnostics of high harmonics of the extreme-ultraviolet free-electron laser light source at SPring-8.

We have developed a cold-target recoil-ion momentum spectroscopy apparatus dedicated to the experiments using the extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan and used it to measure spatial distributions of fundamental, second, and third harmonics at the end station.

Fragmentation channels of K-shell excited rare-gas clusters studied by multiple-ion coincidence momentum imaging.

Multiple-ion coincidence momentum imaging experiments were carried out for K-shell (1s) excited Ar clusters containing about 130 atoms and Kr clusters containing about 30, 90, and 160 atoms. The time-of-flight spectra reveal that the major products of the Coulomb explosion are singly charged ions. With increasing the number of charges generated in clusters, the momentum of monomer ions such as Ar(+) and Kr(+) increases, while that of cluster ions such as Ar(3) (+), Kr(2) (+), and Kr(3) (+) decreases. This observation indicates the site-specific decay process that the heavier ions appear in the central part of clusters. We have also investigated the momentum distribution in various fragmentation channels and the branching ratio of each channel at the Coulomb explosion. When the number N(coin) of coincidently detected ions is four, for example, the most frequent channel from Kr clusters containing 30 atoms is to emit simply four Kr(+) ions, but Kr(2) (+) ions participate in the fragmentation from the larger Kr clusters. The fragmentation channel in which two Ar(2) (+) ions are emitted becomes dominant with increasing N(coin), and the average momentum of Ar(2) (+) ion in this channel is larger than that in the channels where only single Ar(2) (+) is emitted.