Time-diagnostics for improved dynamics experiments at XUV FELs

Drescher, Markus; Frühling, Ulrike; Krikunova, Maria; Maltezopoulos, Theophilos; Wieland, Marek

doi:10.1088/0953-4075/43/19/194010

Cited by 18 publications

(16 citation statements)

References 34 publications

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“…A possibility of measuring the reflection of the probe pulse instead of the transmission is also an option being explored in experiments [38,47]. The present work, however, focuses only on the transmission mode, requiring wideband gap insulators.…”

Section: Materials Previously Used For Pulse-duration Monitoringmentioning

confidence: 99%

“…In addition, femtosecond level jitter between the FEL and a corresponding pump laser has often obscured femtosecond dynamics. Recently developed time-sorting pump-probe techniques allow to probe the electronic or atomic kinetics in irradiated targets with a sub-ten-femtosecond resolution for FLASH and LCLS [22,23,37,38]. The time sorting of data recorded with single-shot detectors allows to exclude jitter between FEL and probe pulse [22].…”

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confidence: 99%

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Femtosecond X-ray induced electron kinetics in dielectrics: application for FEL-pulse-duration monitor

Medvedev

2015

Appl. Phys. B

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regime of photon energy up to 24-25 keV with the pulse duration of a few tens of femtoseconds, possibly reduced further down to a few femtoseconds. The advent of such light sources stimulated rapid advances in many scientific disciplines ranging from atomic physics [6,7], study of molecules and chemical reactions [8,9], to clusters [10,11] and macroscopic objects [12-14] exposed to intense laser fields. They are actively used for creating and probing plasmas [15,16], hot dense matter [16][17][18] and warm dense matter [19,20]. Lower fluences of FELs are used to investigate structural changes within solid-state matter [12,[21][22][23][24]. These new light sources have also found a broad interest in the fields of nanophysics [25], molecular physics and biophysics [26].Insulators irradiated with femtosecond X-ray FEL radiation are observed to undergo a sequence of processes [12,27]. During the pulse, the photoabsorption excites electrons from the valence band, or deep atomic shells, to unoccupied conduction band states. The deep shell atomic holes then decay via Auger processes, which are the dominant relaxation channel for light elements (low-Z) [28]. An Auger decay promotes one more electron from the valence to the conduction band, following the relaxation of the deeper shell hole into the upper shells or the valence band. In case of heavy elements, with multiple shells, an intraatomic Auger cascade involving many steps over different shells is possible, ultimately ending up with multiple holes in the valence band. This process occurs typically on the few femtosecond timescale. The released photo-and Auger electrons scatter inelastically (so-called impact ionization of valence band or deep shell electrons of the material), or elastically (scattering on atoms or phonons without ionization of the target). Each impact ionization event excites one more electron into the conduction band. The impact ionization cascading typically occurs on the femtosecond Abstract Modern X-ray free-electron lasers (FELs) provide pulses with photon energies from a few tens of eV up to the tens of keV and durations as short as only a few femtoseconds. Experimental pump-probe scheme with a FEL pump and a visible light probe of a solid-state target can be used for the pulse-duration monitor on a shot-to-shot basis.To study the electron cascading in different materials used for pulse-duration monitor, XCASCADE, a Monte Carlo model of the X-ray-induced electron cascading within an irradiated target is developed. It is shown here that the electron cascade duration is sensitive to a choice of material. An appropriately selected target can significantly shorten the electron relaxation times. The grounds, upon which such a choice of the material can be made, are discussed. The results suggest that for photon energies of 24 keV, one could achieve direct monitoring of the pulse duration of 40 fs. Further deconvolution of the electron density into the contribution from the pulse itself and from the secondary cascading can increase the resolution up ...

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Section: Materials Previously Used For Pulse-duration Monitoringmentioning

confidence: 99%

mentioning

confidence: 99%

Femtosecond X-ray induced electron kinetics in dielectrics: application for FEL-pulse-duration monitor

Medvedev

2015

Appl. Phys. B

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“…Early synchronization and locking schemes mostly relied on electronic radio-frequency (RF) synchronization (Glownia et al 2010, Redlin et al 2011, where long-term drifts and shot-to-shot jitter of the arrival time of the FEL pulse significantly limited the temporal resolution far beyond the pulse durations of the FEL and the femtosecond laser (Radcliffe et al 2007, Glownia et al 2010, Petrovic et al 2012, Rouzée et al 2013, Schnorr et al 2014b. To address these limitations, x-ray/optical cross-correlators (OXCs) were developed, which measure the relative arrival-time jitter between the FEL and laser pulses on a shot-by-shot basis to offer the ability to correct for this jitter by sorting the data through post-analysis (Gahl et al 2008, Maltezopoulos et al 2008, Azima et al 2009, Drescher et al 2010, Bionta et al 2011, Beye et al 2012, Grguraš et al 2012, Schorb et al 2012, Harmand et al 2013, Riedel et al 2013, Bionta et al 2014, Eckert et al 2015. While such cross-correlation schemes significantly improved the temporal resolution that could be achieved in pumpprobe experiments, the method is applicable only to certain types of experiments.…”

Section: Introductionmentioning

confidence: 99%

Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser

et al. 2017

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In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C 6 H 3 F 2 I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. We discuss in detail the necessary data analysis steps and describe the origin of the timedependent effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.

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“…As a work-around, several diagnostic tools have been developed at FLASH in order to measure pulse by pulse the energy [5], temporal profile [6], and arrival time [7] of the SASE EUV pulses. With this pulse tagging approach, one can categorize and sort the measured data, thereby increasing, for instance, the temporal resolution for dynamic studies [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

A high-harmonic generation source for seeding a free-electron laser at 38 nm

et al. 2013

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Direct seeding with a high-harmonic generation (HHG) source can improve the spectral, temporal, and coherence properties of a free-electron laser (FEL) and shall reduce intensity and arrival-time fluctuations. In the seeding experiment sFLASH at the extreme ultraviolet FEL in Hamburg FLASH, which operates in the selfamplified spontaneous emission mode (SASE), the 21st harmonic of an 800 nm laser is refocused into a dedicated seeding undulator. For seeding, the external light field has to overcome the noise level of SASE; therefore, an efficient coupling between seed pulse and electron bunch is mandatory. Thus, an HHG beam with a proper divergence, width, beam quality, Rayleigh length, pointing stability, single-shot pulse energy, and stability in the 21st harmonic is needed. Here, we present the setup of the HHG source that seeds sFLASH at 38.1 nm, the optimization procedures, and the necessary diagnostics.

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Time-diagnostics for improved dynamics experiments at XUV FELs

Cited by 18 publications

References 34 publications

Femtosecond X-ray induced electron kinetics in dielectrics: application for FEL-pulse-duration monitor

Femtosecond X-ray induced electron kinetics in dielectrics: application for FEL-pulse-duration monitor

Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser

A high-harmonic generation source for seeding a free-electron laser at 38 nm

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