Edwin Divall

Bio: Edwin Divall is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Ultrashort pulse & Diffraction. The author has an hindex of 4, co-authored 8 publications receiving 314 citations.

SwissFEL: The Swiss X-ray Free Electron Laser

Abstract: The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.

Commissioning experience and beam physics measurements at the SwissFEL Injector Test Facility

Abstract: The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

Commissioning experience and beam physics measurements at the SwissFEL Injector Test Facility

Abstract: The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and test bed for the development and realization of SwissFEL, the x-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultralow-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

Hard X-ray transient grating spectroscopy on bismuth germanate

Abstract: Optical-domain transient grating (TG) spectroscopy is a versatile background-free four-wave-mixing technique that is used to probe vibrational, magnetic and electronic degrees of freedom in the time domain1. The newly developed coherent X-ray free-electron laser sources allow its extension to the X-ray regime. X-rays offer multiple advantages for TG: their large penetration depth allows probing the bulk properties of materials, their element specificity can address core excited states, and their short wavelengths create excitation gratings with unprecedented momentum transfer and spatial resolution. Here, we demonstrate TG excitation in the hard X-ray range at 7.1 keV. In bismuth germanate (BGO), the non-resonant TG excitation generates coherent optical phonons detected as a function of time by diffraction of an optical probe pulse. This experiment demonstrates the ability to probe bulk properties of materials and paves the way for ultrafast coherent four-wave-mixing techniques using X-ray probes and involving nanoscale TG spatial periods. A four-wave mixing technique is developed in the hard X-ray range. A diamond phase grating in an X-ray beam path creates a periodic excitation pattern on a sample via the Talbot effect. The response of the periodic excitation is probed by an optical pulse.

Hard X-ray Transient Grating Spectroscopy on Bismuth Germanate

Abstract: Optical-domain Transient Grating (TG) spectroscopy is a versatile background-free four-wave-mixing technique used to probe vibrational, magnetic and electronic degrees of freedom in the time domain. The newly developed coherent X-ray Free Electron Laser sources allow its extension to the X-ray regime. Xrays offer multiple advantages for TG: their large penetration depth allows probing the bulk properties of materials, their element-specificity can address core-excited states, and their short wavelengths create excitation gratings with unprecedented momentum transfer and spatial resolution. We demonstrate for the first time TG excitation in the hard X-ray range at 7.1 keV. In Bismuth Germanate (BGO), the nonresonant TG excitation generates coherent optical phonons detected as a function of time by diffraction of an optical probe pulse. This experiment demonstrates the ability to probe bulk properties of materials and paves the way for ultrafast coherent four-wave-mixing techniques using X-ray probes and involving nanoscale TG spatial periods.

SwissFEL: The Swiss X-ray Free Electron Laser

Abstract: The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.

Direct Measurement of Room-Temperature Nondiffusive Thermal Transport Over Micron Distances in a Silicon Membrane

Abstract: The "textbook" phonon mean free path of heat carrying phonons in silicon at room temperature is ∼40 nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range ∼1-10 μm. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.

Attosecond time–energy structure of X-ray free-electron laser pulses

Abstract: The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam

Abstract: We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-A wavelength with pulse energies of more than 500 μJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation. The first lasing results at SwissFEL, an X-ray free-electron laser, are presented, highlighting the facility’s unique capabilities. A general comparison to other major facilities is also provided.

Femtosecond-to-millisecond structural changes in a light-driven sodium pump.

Abstract: Light-driven sodium pumps actively transport small cations across cellular membranes1. These pumps are used by microorganisms to convert light into membrane potential and have become useful optogenetic tools with applications in neuroscience. Although the resting state structures of the prototypical sodium pump Krokinobacter eikastus rhodopsin 2 (KR2) have been solved2,3, it is unclear how structural alterations over time allow sodium to be translocated against a concentration gradient. Here, using the Swiss X-ray Free Electron Laser4, we have collected serial crystallographic data at ten pump-probe delays from femtoseconds to milliseconds. High-resolution structural snapshots throughout the KR2 photocycle show how retinal isomerization is completed on the femtosecond timescale and changes the local structure of the binding pocket in the early nanoseconds. Subsequent rearrangements and deprotonation of the retinal Schiff base open an electrostatic gate in microseconds. Structural and spectroscopic data, in combination with quantum chemical calculations, indicate that a sodium ion binds transiently close to the retinal within one millisecond. In the last structural intermediate, at 20 milliseconds after activation, we identified a potential second sodium-binding site close to the extracellular exit. These results provide direct molecular insight into the dynamics of active cation transport across biological membranes.