49 research outputs found
Nanoplasma Dynamics of Single Large Xenon Clusters Irradiated with Superintense X-Ray Pulses from the Linac Coherent Light Source Free-Electron Laser
No full textHetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics
No full textNew capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF molecules following X-ray absorption at the Xe site
Spontaneous emission control of single quantum dots in bottom-up nanowire waveguides
No full textNanowire waveguides with controlled shape are promising for engineering the collection efficiency of quantum light sources. We investigate the exciton lifetime in individual InAsP quantum dots, perfectly positioned on-axis of InP nanowire waveguides. We demonstrate control over the quantum dot spontaneous emission by varying the nanowire diameter in e-beam patterned arrays, which modifies the coupling efficiency of the emitter to the fundamental waveguide mode. The spontaneous emission rate is inhibited by a factor of 12 in thin nanowires compared to nanowires with optimized waveguide diameter. From the measured inhibition factor, we determine a high radiative yield exceeding 92% in bottom-up grown nanowires.QN/Quantum NanoscienceApplied Science
Multiphoton ionization of Xenon at the LCLS free-electron laser
No full textWith the first X-ray free-electron laser (FEL), the Linac Coherent Light Source (LCLS), multiphoton ionization has been pushed to a new regime, where atoms and molecules are not just ionized by a series of valence ionizations but "from the inside out". At unprecedented high intensities and short pulse durations in the soft X-ray regime, a series of inner-shell photoionizations followed by cascades of Auger decays was observed to lead to highly charged final states in rare gases such as Ne, Ar, Kr, and Xe. Ion time-of-flight and fluorescence spectra were recorded for different FEL pulse energies and pulse lengths and compared to theoretical models to explain the underlying processes that lead to unexpectedly high charge states in Xe
Femtosecond response of polyatomic molecules to ultra-intense hard X-rays
No full textX-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions1, 2, 3, 4, 5, 6, 7. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 1020 watts per square centimetre)3, 5. However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities8, 9, 10, 11, 12, 13, 14, 15, 16, 17. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption8, 12, 13, 18, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge14, 15, 16, 17, 19, 20. In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure2, 3—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects21, 22 and has been suggested as a way of phasing the diffraction data23, 24. On the basis of experiments using either soft or less-intense hard X-rays14, 15, 16, 17, 18, 19, 25, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 1020 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section. This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse. Our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible
Ionization dynamics in expanding clusters studied by XUV pump probe spectroscopy
No full texthe expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x ray extreme ultraviolet XUV pulses were studied with pump probe spectroscopy using the autocorrelator setup of the Free Electron LASer in Hamburg FLASH facility. The ionization by the first XUV pulse of 92 eV photon energy 8 1012 W cm amp; 8722;2 leads to the generation of a large number of quasi free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe 4 1013 W cm amp; 8722;2 pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 1 3 p
Ionization dynamics of Xe nanoplasma formation studied with XUV fluorescence spectroscopy
No full textIntense pulses from a short wavelength free-electron laser turn xenon nanoparticles into a high energy density nanoplasma within femtoseconds. Recently, the generation of multiply charged xenon ions during the initial phase of plasma evolution has been studied by energy-resolved XUV fluorescence detection as a function of cluster size and cluster composition [1]. In the present contribution we give a detailed analysis of the corresponding radiative transitions after resonant excitation of the 4d electron shell at intensities of 2 × 10 − 2.45 × 10Wcm. The evaluation of charge-state specific fluorescence yields as a function of FEL power density demonstrates that plasma effects such as ionization potential lowering, electron impact excitation, ionization, and energy redistribution govern the laser-induced non-equilibrium dynamics in xenon clusters
Hidden Charge States in Soft-X-Ray Laser-Produced Nanoplasmas Revealed by Fluorescence Spectroscopy
No full textHighly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least 11+
