Conventional synchrotron radiation sources enable the structure of matter to be studied at near-atomic spatial resolution and picosecond temporal resolution. Free-electron lasers promise to extend ...this down to femtosecond timescales. The process by which free-electron lasers amplify synchrotron light-known as self-amplified spontaneous emission-is only partially temporally coherent, but this can be improved by seeding it with an external laser. Here we explore the use of seed light produced by high-order harmonic generation in a gas, covering wavelengths from the ultraviolet to soft X-rays. Using the SPring-8 Compact SASE Source test accelerator, we demonstrate an increase of three orders of magnitude in the intensity of the fundamental radiation at 160 nm, halving of the free-electron laser saturation length, and the generation of nonlinear harmonics at 54 nm and 32 nm. The low seed level used in this demonstration suggests that nonlinear harmonic schemes should enable the generation of fully coherent soft X-rays at wavelengths down to the so-called 'water window', vital for the study of biological samples.
The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×10(11) photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid ...sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.
Controlling attosecond electron wave packets and soft X-ray pulses represents a formidable challenge of general implication to many areas of science. A strong laser field interacting with atoms or ...molecules drives ultrafast intra-atomic/molecular electron wave packets on a subfemtosecond timescale, resulting in the emission of attosecond bursts of extreme-ultraviolet light. Controlling the intra-atomic/molecular electron dynamics enables steering of the attosecond emission. Here, we carry out a coherent control in linear molecules, where the interaction of the laser-driven electron wave packet with the core leads to quantum interferences. We demonstrate that these interferences can be finely controlled by turning the molecular axis relative to the laser polarization, that is, changing the electron recollision angle. The wave-packet coulombic distortion modifies the spectral phase jump measured in the extreme-ultraviolet emission. Our attosecond control of the interference results in attosecond pulse shaping, useful for future applications in ultrafast coherent control of atomic and molecular processes.
Attosecond Synchronization of High-Harmonic Soft X-rays Mairesse, Y.; de Bohan, A.; Frasinski, L. J. ...
Science (American Association for the Advancement of Science),
11/2003, Letnik:
302, Številka:
5650
Journal Article
Recenzirano
Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should ...result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attoseconds in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter.
Recovering the three-dimensional (3D) properties of artificial or biological systems using low X-ray doses is challenging as most techniques are based on computing hundreds of two-dimensional (2D) ...projections. The requirement for a low X-ray dose also prevents single-shot 3D imaging using ultrafast X-ray sources. Here we show that computed stereo vision concepts can be applied to X-rays. Stereo vision is important in the field of machine vision and robotics. We reconstruct two X-ray stereo views from coherent diffraction patterns and compute a nanoscale 3D representation of the sample from disparity maps. Similarly to brain perception, computed stereo vision algorithms use constraints. We demonstrate that phase-contrast images relax the disparity constraints, allowing occulted features to be revealed. We also show that by using nanoparticles as labels we can extend the applicability of the technique to complex samples. Computed stereo X-ray imaging will find application at X-ray free-electron lasers, synchrotrons and laser-based sources, and in industrial and medical 3D diagnosis methods.Stereo images of gold nanoparticles in a pyramid shape are reconstructed from X-ray coherent diffraction patterns. Depth information is retrieved by computing disparity maps without a priori knowledge of the sample shape.
A 58-year-old man suffering from active smoking and alcoholism was admitted to ICU for pneumococcal meningitis, pneumonia, and endocarditis. Tree blood cultures showed the presence of Streptococcus ...pneumoniae. The patient was diagnosed with Austrian syndrome, which is a triad consisting of pneumonia, endocarditis, and meningitis, caused by S. pneumonia.
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