Communication: The formation of rarefaction waves in semiconductors after ultrashort excitation probed by grazing incidence ultrafast time-resolved x-ray diffraction

Table-top laser-driven hard x-ray sources with kilohertz repetition rates are an attractive alternative to large-scale accelerator-based systems and have found widespread applications in x-ray studies of ultrafast structural dynamics. Hard x-ray pulses of 100 fs duration have been generated at the Cu Kα wavelength with a photon flux of up to 109 photons per pulse into the full solid angle, perfectly synchronized to the sub-100-fs optical pulses from the driving laser system. Based on spontaneous x-ray emission, such sources display a particular noise behavior which impacts the sensitivity of x-ray diffraction experiments. We present a detailed analysis of the photon statistics and temporal fluctuations of the x-ray flux, together with experimental strategies to optimize the sensitivity of optical pump/x-ray probe experiments. We demonstrate measurements close to the shot-noise limit of the x-ray source.

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“…Most of them are based on a reference x-ray flux derived from the same source and detected with a second detector. 26–31 …”

Section: Resultsmentioning

confidence: 99%

Towards shot-noise limited diffraction experiments with table-top femtosecond hard x-ray sources

Holtz

Hauf

Weißhaupt

et al. 2017

Structural Dynamics

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“…To account for the variation of the X-ray flux due to both long-term drifts and short-term fluctuations 62 , a "direct" normalization [62][63][64][65] scheme has been implemented in which a GaAs crystal is properly placed at a second output of the X-ray source chamber and the integrated diffraction signal of its (111)-reflection is monitored by a large area (diameter 10 mm) X-ray sensitive avalanche photo-diode (APD). This allow to normalize the diffraction signals recorded by the CCD with an accuracy of better than 2%.…”

Section: Experimental Realizationmentioning

confidence: 99%

Time-resolved diffraction with an optimized short pulse laser plasma X-ray source

Afshari

Krumey

Menn

et al. 2020

Structural Dynamics

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We present a set-up for time-resolved X-ray diffraction based on a short pulse, laser-driven plasma X-ray source. The employed modular design provides high flexibility to adapt the set-up to the specific requirements (e.g. X-ray optics, sample environment) of particular applications. The configuration discussed here has been optimized towards high angular/momentum resolution and uses K α -radiation (4.51 keV) from a Ti wire-target in combination with a toroidally bent crystal for collection, monochromatization and focusing of the emitted radiation. 2 × 10 5 Ti-K α1 photons per pulse with 10 −4 relative bandwidth are delivered to the sample at 10 Hz repetition rate. This allows for high dynamic range (10 4 ) measurements of transient changes of the rocking curves of materials as for example induced by laser-triggered strain waves. PACS numbers: 78.47.J-, 61.05.C, 63.30.dd a) Klaus.Sokolowski-Tinten@uni-due.de

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“…We demonstrate that time-resolved grazing incidence X-ray diffraction (GIXD) directly measures the displacement waves in molecular organic films to a detail that allows us to distinguish between different excitation mechanisms. There have been a number of recent time-resolved X-ray studies of phonon dynamics in inorganic materials, 18 but herein the focus is on how the organic matter is impacted by light. The light–solid matter interactions of the organic material are central and have been addressed in previous studies involving femtosecond lasers 19 but rarely with time-resolved diffraction.…”

Section: Introductionmentioning

confidence: 99%

Tuning and Tracking of Coherent Shear Waves in Molecular Films

Lemke¹,

Breiby

Ejdrup³

et al. 2018

ACS Omega

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We have determined the time-dependent displacement fields in molecular sub-micrometer thin films as response to femtosecond and picosecond laser pulse heating by time-resolved X-ray diffraction. This method allows a direct absolute determination of the molecular displacements induced by electron–phonon interactions, which are crucial for, for example, charge transport in organic electronic devices. We demonstrate that two different modes of coherent shear motion can be photoexcited in a thin film of organic molecules by careful tuning of the laser penetration depth relative to the thickness of the film. The measured response of the organic film to impulse heating is explained by a thermoelastic model and reveals the spatially resolved displacement in the film. Thereby, information about the profile of the energy deposition in the film as well as about the mechanical interaction with the substrate material is obtained.

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Communication: The formation of rarefaction waves in semiconductors after ultrashort excitation probed by grazing incidence ultrafast time-resolved x-ray diffraction

Cited by 8 publications

References 29 publications

Towards shot-noise limited diffraction experiments with table-top femtosecond hard x-ray sources

Towards shot-noise limited diffraction experiments with table-top femtosecond hard x-ray sources

Time-resolved diffraction with an optimized short pulse laser plasma X-ray source

Tuning and Tracking of Coherent Shear Waves in Molecular Films

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