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Comparative Study of Bunch Length And Arrival Time Measurements at FLASH

Description: Diagnostic devices to precisely measure the longitudinal electron beam profile and the bunch arrival time require elaborate new instrumentation techniques. At FLASH, two entirely different methods are used. The bunch profile can be determined with high precision by a transverse deflecting RF structure, but the method is disruptive and does not allow to monitor multiple bunches in a macro-pulse train. It is therefore complemented by two non-disruptive electrooptical devices, called EO and TEO. The EO setup uses a dedicated diagnostic laser synchronized to the machine RF. The longitudinal electron beam profile is encoded in the intensity profile of a chirped laser pulse and analyzed by looking at the spectral composition of the pulse. The second setup, TEO, utilizes the TiSa-based laser system used for pump-probe experiments. Here, the temporal electron shape is encoded into the spatial dimension of the laser pulse by an intersection angle between the laser and the electron beam at the EO-crystal. In this paper, we present a comparative study of bunch length and arrival time measurements performed simultaneously with all three experimental techniques.
Date: April 16, 2007
Creator: Schlarb, H.; Azima, A.; Dusterer, S.; Huning, M.; Knabbe, E.A.; Roehrs, M. et al.
Partner: UNT Libraries Government Documents Department

Thomson scattering from near-solid density plasmas using soft x-ray free electron lasers

Description: We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode.
Date: November 21, 2006
Creator: Holl, A; Bornath, T; Cao, L; Doppner, T; Dusterer, S; Forster, E et al.
Partner: UNT Libraries Government Documents Department

Thomson Scattering at FLASH - Status Report

Description: The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at near-solid density plasmas as a diagnostic method which allows the determination of plasma temperatures and densities in the warm dense matter (WDM) regime (free electron density of n{sub e} = 10{sup 21}-10{sup 26} cm{sup -3} with temperatures of several eV). The WDM regime [1] at near-solid density (n{sub e} = 10{sup 21}-10{sup 22} cm{sup -3}) is of special interest because, it is where the transition from an ideal plasma to a degenerate, strongly coupled plasma occurs. A systematic understanding of this largely unknown WDM domain is crucial for the modeling and understanding of contemporary plasma experiments, like laser shock-wave or Z-pinch experiments as well as for inertial confinement fusion (ICF) experiments as the plasma evolution follows its path through this domain.
Date: November 28, 2007
Creator: Toleikis, S; Bornath, T; Cao, L; Doppner, T; Dusterer, S; Faustlin, R et al.
Partner: UNT Libraries Government Documents Department

Investigating two-photon double ionization of D2 by XUV-Pump -- XUV-Probe experiments at FLASH

Description: Using a novel split-mirror set-up attached to a Reaction Microscope at the Free electron LASer in Hamburg (FLASH) we demonstrate an XUV-pump -- XUV-probe ((hbar omega = 38 eV) experiment by tracing the ultra-fast nuclear wave-packet motion in the D2+ (1s sigma g-state) with<10 fs time resolution. Comparison with time-dependent calculations yields excellent agreement with the measured vibrational period of 22+-4 fs in D2+, points to the importance of the inter-nuclear distance dependent ionization probability and paves the way to control sequential and non-sequential two-photon double ionization contributions.
Date: August 2, 2010
Creator: Collaboration, FLASH; Jiang, Y.; Rudenko, A.; Perez-Torres, J.; Foucar, L.; Kurka, M. et al.
Partner: UNT Libraries Government Documents Department

Ultrafast Extreme Ultraviolet Induced Isomerization of Acetylene Cations

Description: Ultrafast isomerization of acetylene cations ([HC = CH]{sup +}) in the low-lying excited A{sup 2}{Sigma}{sub g}{sup +} state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C{sup +} + CH{sub 2}{sup +} as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52 {+-} 15 fs in a kinetic energy release (KER) window of 5.8 < KER < 8 eV, providing clear evidence for the existence of a fast, nonradiative decay channel.
Date: June 17, 2011
Creator: Jiang, Y.; Rudenko, Artem; Herrwerth, O.; Foucar, L.; Kurka, M.; Kuhnel, K. et al.
Partner: UNT Libraries Government Documents Department

Femtosecond Diffractive Imaging with a Soft-X-ray Free-Electron Laser

Description: Theory predicts that with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus, or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft X-ray free-electron laser. An intense 25 fs, 4 x 10{sup 13} W/cm{sup 2} pulse, containing 10{sup 12} photons at 32 nm wavelength, produced a coherent diffraction pattern from a nano-structured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage, and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one.
Date: March 13, 2006
Creator: Chapman, H N; Barty, A; Bogan, M; Boutet, S; Frank, M; Hau-Riege, S P et al.
Partner: UNT Libraries Government Documents Department