Spatial and temporal pre-alignment of an X-ray split-and-delay unit by laser light interferometry

Roseker, Wojciech; Lee, S.; Walther, Michael; Rysov, Rustam; Sprung, Michael; Grübel, G.

doi:10.1063/1.5089496

Cited by 3 publications

(2 citation statements)

References 35 publications

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“…Our result reveals that the spatial part of the coherence is well preserved and that only one or two temporal modes are transmitted improving the longitudinal coherence of the radiation. We also demonstrated its femtosecond time-delay capability and stability via a low coherence light interferometry 51 .…”

Section: Discussionmentioning

confidence: 98%

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay

Roseker

Lee

Walther

et al. 2020

Sci Rep

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the ability to deliver two coherent X-ray pulses with precise time-delays ranging from a few femtoseconds to nanoseconds enables critical capabilities of probing ultra-fast phenomena in condensed matter systems at X-ray free electron laser (feL) sources. Recent progress made in the hard X-ray split-and-delay optics developments now brings a very promising prospect for resolving atomic-scale motions that were not accessible by previous time-resolved techniques. Here, we report on characterizing the spatial and temporal coherence properties of the hard X-ray feL beam after propagating through split-and-delay optics. Speckle contrast analysis of small-angle scattering measurements from nanoparticles reveals well-preserved transverse coherence of the beam. Measuring intensity fluctuations from successive X-ray pulses also reveals that only single or double temporal modes remain in the transmitted beam, corresponding to nearly fourier transform limited pulses. X-ray Free Electron Lasers (XFEL) based on Self Amplified Spontaneous Emission (SASE) deliver ultra-fast and spatially highly coherent hard X-ray radiation with extreme peak brightness (~10 12 photons in a single pulse) making them ideal tools for studying atomic-scale dynamics in various condensed matter systems. The Linac Coherent Light Source (USA) was the first FEL to demonstrate lasing in the hard X-ray regime 1 followed by SACLA (Japan) 2 , PAL-FEL (South Korea) 3 , European XFEL (Germany) 4 and SwissFEL 5. The most prominent time-resolved techniques used at the storage rings such as optical laser pump and X-ray probe 6-9 methods or X-ray photon correlation spectroscopy (XPCS) 10 have in the meantime also been recently demonstrated at the FEL sources 11-14. The pump-probe approach has benefitted greatly from using femtosecond X-ray pulse duration provided at FEL facilities complemented by state of the art timing synchronisation schemes between optical laser and X-ray pulses 15,16. These capabilities have enabled elaborate pump-probe 17-19 and single-shot coherent imaging experiments 20,21. However, replicating XPCS experiments at FELs is much more challenging because the intrinsic time-structure of the FEL sources is unsuitable for studying high-speed dynamical processes in many materials. Currently, most of FELs generate discrete bursts of X-ray radiation at a repetition rate ranging typically between

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Section: Discussionmentioning

confidence: 98%

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay

Roseker

Lee

Walther

et al. 2020

Sci Rep

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“…Experimental schemes providing two XUV pulses of adjustable delays are also central in ultrafast spectroscopy, may it be attosecond-pump/attosecond-probe [8] or attosecond interferometry experiments [15]. In the absence of beam splitters in the XUV spectral range, several experimental arrangements were developed [16][17][18][19][20][21][22][23], some of which consist in splitting a mid-infrared laser pulse in two replicas used to generate attosecond pulses from two spatially separated sources through High order Harmonic Generation (HHG) in gas [24,25] . In this case, the delay between the two XUV pulses is directly controlled by the delay between the two replicas of the HHG driver field.…”

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confidence: 99%

High complexity femtosecond pulse duplicator

Camper

2020

Opt. Express

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This paper presents a theoretical and numerical study of a 0-π fan-out phase grating placed in the Fourier plane of a spatio-spectral pulse shaper followed by a spherical focusing lens. It is shown that this device acts as a high complexity femtosecond pulse duplicator designed for two source interferometry. At the focus of the lens, the electric field displays two spatially separated intense spots in which relative delay can be continuously tuned over 4 orders of magnitude, typically from a few attoseconds to a few tens of femtoseconds. Because the two pulses do not spatially overlap, their intensity remains unchanged when the relative delay is smaller than the pulse duration. Detailed simulations of the shaped electric field are presented.

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Realizing split-pulse x-ray photon correlation spectroscopy to measure ultrafast dynamics in complex matter

Sun

Dunne

Fuoss

et al. 2020

Phys. Rev. Research

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Split-pulse x-ray photon correlation spectroscopy has been proposed as one of the unique capabilities made possible with the x-ray free electron lasers. It enables characterization of atomic scale structural dynamics that dictates the macroscopic properties of various disordered material systems. Central to the experimental concept are x-ray optics that are capable of splitting individual coherent femtosecond x-ray pulse into two distinct pulses, introduce an adjustable time delay between them, and then recombine the two pulses at the sample position such that they generate two coherent scattering patterns in rapid succession. Recent developments in such optics showed that, while true 'amplitude splitting' optics at hard x-ray wavelengths remains a technical challenge, wavefront and wavelength splitting are both feasible, able to deliver two micron sized focused beams to the sample with sufficient relative stability. Here, we however show that the conventional approach to speckle visibility spectroscopy using these beam splitting techniques can be problematic, even leading to a decoupling of speckle visibility and material dynamics. In response, we discuss the details of the experimental approaches and data analysis protocols for addressing issues caused by subtle beam dissimilarities for both wavefront and wavelength splitting setups. We also show that in some scattering geometries, the Q-space mismatch can be resolved by using two beams of slightly different incidence angle and slightly different wavelengths at the same time. Instead of measuring the visibility of weak speckle patterns, the time correlation in sample structure is encoded in the 'side band' of the spatial autocorrelation of the summed speckle patterns, and can be retrieved straightforwardly from the experimental data. We demonstrate this with a numerical simulation.

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Spatial and temporal pre-alignment of an X-ray split-and-delay unit by laser light interferometry

Abstract: Development of a hard X-ray split-and-delay line and performance simulations for twocolor pump-probe experiments at the European XFEL Review of Scientific Instruments 89, 063121 (2018);

Cited by 3 publications

References 35 publications

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay

High complexity femtosecond pulse duplicator

Realizing split-pulse x-ray photon correlation spectroscopy to measure ultrafast dynamics in complex matter

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