Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction.

One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.

Towards X-ray transient grating spectroscopy.

The extension of transient grating spectroscopy to the x-ray regime will create numerous opportunities, ranging from the study of thermal transport in the ballistic regime to charge, spin, and energy transfer processes with atomic spatial and femtosecond temporal resolution. Studies involving complicated split-and-delay lines have not yet been successful in achieving this goal. Here we propose a novel, simple method based on the Talbot effect for converging beams, which can easily be implemented at current x-ray free electron lasers. We validate our proposal by analyzing printed interference patterns on polymethyl methacrylate and gold samples using ∼3 keV X-ray pulses.

Symmetry breakdown of electron emission in extreme ultraviolet photoionization of argon.

Short wavelength free-electron lasers (FELs), providing pulses of ultrahigh photon intensity, have revolutionized spectroscopy on ionic targets. Their exceptional photon flux enables multiple photon absorptions within a single femtosecond pulse, which in turn allows for deep insights into the photoionization process itself as well as into evolving ionic states of a target. Here we employ ultraintense pulses from the FEL FERMI to spectroscopically investigate the sequential emission of electrons from gaseous, atomic argon in the neutral as well as the ionic ground state. A pronounced forward-backward symmetry breaking of the angularly resolved emission patterns with respect to the light propagation direction is experimentally observed and theoretically explained for the region of the Cooper minimum, where the asymmetry of electron emission is strongly enhanced. These findings aim to originate a better understanding of the fundamentals of photon momentum transfer in ionic matter.

Extreme ultraviolet resonant inelastic X-ray scattering (RIXS) at a seeded free-electron laser.

In the past few years, we have been witnessing an increased interest for studying materials properties under non-equilibrium conditions. Several well established spectroscopies for experiments in the energy domain have been successfully adapted to the time domain with sub-picosecond time resolution. Here we show the realization of high resolution resonant inelastic X-ray scattering (RIXS) with a stable ultrashort X-ray source such as an externally seeded free electron laser (FEL). We have designed and constructed a RIXS experimental endstation that allowed us to successfully measure the d-d excitations in KCoF3 single crystals at the cobalt M2,3-edge at FERMI FEL (Elettra-Sincrotrone Trieste, Italy). The FEL-RIXS spectra show an excellent agreement with the ones obtained from the same samples at the MERIXS endstation of the MERLIN beamline at the Advanced Light Source storage ring (Berkeley, USA). We established experimental protocols for performing time resolved RIXS experiments at a FEL source to avoid X ray-induced sample damage, while retaining comparable acquisition time to the synchrotron based measurements. Finally, we measured and modelled the influence of the FEL mixed electromagnetic modes, also present in externally seeded FELs, and the beam transport with ~120 meV experimental resolution achieved in the presented RIXS setup.

The FERMI free-electron lasers.

FERMI is a seeded free-electron laser (FEL) facility located at the Elettra laboratory in Trieste, Italy, and is now in user operation with its first FEL line, FEL-1, covering the wavelength range between 100 and 20 nm. The second FEL line, FEL-2, a high-gain harmonic generation double-stage cascade covering the wavelength range 20-4 nm, has also completed commissioning and the first user call has been recently opened. An overview of the typical operating modes of the facility is presented.

Four-wave mixing experiments with extreme ultraviolet transient gratings.

Four-wave mixing (FWM) processes, based on third-order nonlinear light-matter interactions, can combine ultrafast time resolution with energy and wavevector selectivity, and enable the exploration of dynamics inaccessible by linear methods. The coherent and multi-wave nature of the FWM approach has been crucial in the development of advanced technologies, such as silicon photonics, subwavelength imaging and quantum communications. All these technologies operate at optical wavelengths, which limits the spatial resolution and does not allow the probing of excitations with energy in the electronvolt range. Extension to shorter wavelengths--that is, the extreme ultraviolet and soft-X-ray ranges--would allow the spatial resolution to be improved and the excitation energy range to be expanded, as well as enabling elemental selectivity to be achieved by exploiting core resonances. So far, FWM applications at such wavelengths have been prevented by the absence of coherent sources of sufficient brightness and of suitable experimental set-ups. Here we show how transient gratings, generated by the interference of coherent extreme-ultraviolet pulses delivered by the FERMI free-electron laser, can be used to stimulate FWM processes at suboptical wavelengths. Furthermore, we have demonstrated the possibility of observing the time evolution of the FWM signal, which shows the dynamics of coherent excitations as molecular vibrations. This result opens the way to FWM with nanometre spatial resolution and elemental selectivity, which, for example, would enable the investigation of charge-transfer dynamics. The theoretical possibility of realizing these applications has already stimulated ongoing developments of free-electron lasers: our results show that FWM at suboptical wavelengths is feasible, and we hope that they will enable advances in present and future photon sources.

Magnetization and microstructure dynamics in Fe/MnAs/GaAs(001): Fe magnetization reversal by a femtosecond laser pulse.

Thin film magnetization reversal without applying external fields is an attractive perspective for applications in sensors and devices. One way to accomplish it is by fine-tuning the microstructure of a magnetic substrate via temperature control, as in the case of a thin Fe layer deposited on a MnAs/GaAs(001) template. This work reports a time-resolved resonant scattering study exploring the magnetic and structural properties of the Fe/MnAs system, using a 100 fs optical laser pulse to trigger local temperature variations and a 100 fs x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics. The experiment provides direct evidence that a single optical laser pulse can reverse the Fe magnetization locally. It reveals that the time scale of the magnetization reversal is slower than that of the MnAs structural transformations triggered by the optical pulse, which take place after a few picoseconds already.

Determining the polarization state of an extreme ultraviolet free-electron laser beam using atomic circular dichroism.

Ultrafast extreme ultraviolet and X-ray free-electron lasers are set to revolutionize many domains such as bio-photonics and materials science, in a manner similar to optical lasers over the past two decades. Although their number will grow steadily over the coming decade, their complete characterization remains an elusive goal. This represents a significant barrier to their wider adoption and hence to the full realization of their potential in modern photon sciences. Although a great deal of progress has been made on temporal characterization and wavefront measurements at ultrahigh extreme ultraviolet and X-ray intensities, only few, if any progress on accurately measuring other key parameters such as the state of polarization has emerged. Here we show that by combining ultra-short extreme ultraviolet free electron laser pulses from FERMI with near-infrared laser pulses, we can accurately measure the polarization state of a free electron laser beam in an elegant, non-invasive and straightforward manner using circular dichroism.

Two-colour pump-probe experiments with a twin-pulse-seed extreme ultraviolet free-electron laser.

Exploring the dynamics of matter driven to extreme non-equilibrium states by an intense ultrashort X-ray pulse is becoming reality, thanks to the advent of free-electron laser technology that allows development of different schemes for probing the response at variable time delay with a second pulse. Here we report the generation of two-colour extreme ultraviolet pulses of controlled wavelengths, intensity and timing by seeding of high-gain harmonic generation free-electron laser with multiple independent laser pulses. The potential of this new scheme is demonstrated by the time evolution of a titanium-grating diffraction pattern, tuning the two coherent pulses to the titanium M-resonance and varying their intensities. This reveals that an intense pulse induces abrupt pattern changes on a time scale shorter than hydrodynamic expansion and ablation. This result exemplifies the essential capabilities of the jitter-free multiple-colour free-electron laser pulse sequences to study evolving states of matter with element sensitivity.

Invited article: Coherent imaging using seeded free-electron laser pulses with variable polarization: first results and research opportunities.

FERMI@Elettra, the first vacuum ultraviolet and soft X-ray free-electron laser (FEL) using by default a "seeded" scheme, became operational in 2011 and has been opened to users since December 2012. The parameters of the seeded FERMI FEL pulses and, in particular, the superior control of emitted radiation in terms of spectral purity and stability meet the stringent requirements for single-shot and resonant coherent diffraction imaging (CDI) experiments. The advantages of the intense seeded FERMI pulses with variable polarization have been demonstrated with the first experiments performed using the multipurpose experimental station operated at the diffraction and projection imaging (DiProI) beamline. The results reported here were obtained with fixed non-periodic targets during the commissioning period in 2012 using 20-32 nm wavelength range. They demonstrate that the performance of the FERMI FEL source and the experimental station meets the requirements of CDI, holography, and resonant magnetic scattering in both multi- and single-shot modes. Moreover, we present the first magnetic scattering experiments employing the fully circularly polarized FERMI pulses. The ongoing developments aim at pushing the lateral resolution by using shorter wavelengths provided by double-stage cascaded FERMI FEL-2 and probing ultrafast dynamic processes using different pump-probe schemes, including jitter-free seed laser pump or FEL-pump∕FEL-probe with two color FEL pulses generated by the same electron bunch.

The photon analysis, delivery, and reduction system at the FERMI@Elettra free electron laser user facility.

The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste laboratory in Trieste (Italy). It will cover the wavelength range from 100 to about 5 nm in the fundamental and 3 or 1 nm using the third harmonic. We report the layout of the photon beam diagnostics section, the radiation transport system to the experimental area, and the photon beam distribution system. Due to the peculiar characteristics of the emitted FEL radiation (high peak power, short pulse length, and statistical variation of the emitted intensity and distribution), the realization of the diagnostics system is particularly challenging. The end users are interested in parameters such as the radiation pulse intensity and spectral distribution, as well as in the possibility to attenuate the intensity. In order to accomplish these tasks, a photon analysis, delivery, and reduction system is now under development and construction and is presented here. This system will work on-line producing pulse-resolved information and will let users keep track of the photon beam parameters during the experiments.

The neuropsychological examination of naming in Lyme borreliosis.

Although subjective complaints of word finding and naming deficits are commonly reported by patients with Lyme Borreliosis (LB), the existence of these disturbances has not been thoroughly investigated. Forty-four patients with LB and 43 healthy controls were administered a symptom questionnaire, the Boston Naming Test (BNT), the Controlled Oral Word Association Test (COWAT), and a series of category naming tasks. LB patients had a higher rate of complaints of word-finding disturbance (55% vs. 14%). Lower mean scores were observed on the BNT, but not on the COWAT, nor on category naming tasks. Thirty-six percent of the LB sample exhibited BNT scores in the impaired range. BNT scores in this group were correlated with a measure of memory retrieval, but not with verbal fluency indexes. There was no relation between naming scores and depression. LB patients exhibit impairments in word finding that appear to be secondary to a generalized retrieval deficit.

Ethnicity, aggression and serum creatine kinase in hospitalized male forensic patients.

OBJECTIVE: This study examined the relationship of serum creatine kinase (CK) levels with aggressive behavior as a function of psychosis and ethnicity in a sample of violent forensic patients. DESIGN: CK levels were determined on admission in a sample of 195 males consecutively admitted to a forensic hospital. The patients' aggressive behavior during their hospital stay was monitored using the Overt Aggression Scale (OAS). All data for this study was archival and gathered from hospital records. METHODS: Multivariate analysis of variance was used to examine whether African-American and Caucasian patients differed in serum CK levels and severity, frequency, and type (verbal vs physical) of aggression. T-tests were performed to compare ethnic groups in terms of age, weight, height, systolic and diastolic blood pressure. All patients who had been in restraints, had been administered intramuscular medications, had a history of drug or alcohol abuse, and were classified as schizophrenic were compared using chi-square analysis. For each of these variables further comparisons were made of CK levels between African-American and Caucasian patients. RESULTS: Mean serum CK in African-American patients was 64% higher than in Caucasians. African Americans displayed significantly greater physical aggression than Caucasian patients. In addition, African-American patients with a diagnosis of schizophrenia had significantly higher CK levels than African Americans with other diagnoses, with no significant differences related to schizophrenia noted within the Caucasian group. No significant differences in aggressive behavior related to schizophrenia were found in African-American patients. CONCLUSIONS: This study confirms the findings of previous reports which observed higher CK levels in African Americans than in Caucasians. It is also proposed that a confluence of physiologic and psychosocial factors may affect biological marker presentation, particularly as manifest in CK differences between ethnic groups.