Albert Romann

Bio: Albert Romann is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Laser & Laser pumping. The author has an hindex of 5, co-authored 11 publications receiving 304 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.

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.

Outline of a dielectric laser acceleration experiment at SwissFEL

Abstract: The Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation for a 5 year period, pursues basic research and development for a super-compact accelerator on a chip, where the accelerating structure is a dielectric microstructure excited by femtosecond laser pulses. The Paul Scherrer Institute (PSI) will contribute to this by providing the international collaboration access to the high-brightness electron beams in SwissFEL, where we plan to do a proof-of-principle demonstration of the acceleration of a highly relativistic beam. In this contribution we present the conceptual layout of the experiment, in which we will focus the beam down to sub-micrometer beam sizes. Start-to-end simulation results of the tracked electron beam, and first calculations of the accelerating field of the microstructure will be shown.

The ACHIP experimental chambers at the Paul Scherrer Institut

Abstract: The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, with the goal of demonstrating that laser-driven accelerator can be integrated on a chip to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.

REFERENCE DISTRIBUTION AND SYNCHRONIZATION SYSTEM FOR SwissFEL: CONCEPT AND FIRST RESULTS

Abstract: The development of the SwissFEL [1] reference distribution and synchronization system is driven by demanding stability specs of LLRF-, beam arrival time monitors (BAM) and laser systems on one and cost issues, high reliability/availability and flexibility on the other hand. Key requirements for the reference signals are <10fsrms jitter well as down to 10fspp temporal drift stability (goal) for the most critical clients (BAM, pulsed lasers). The system essentially consists of a phase locked optical master oscillator (OMO) with an optical power amplifier/splitter, from which mutually phase locked optical reference pulses as well as RF reference signals are derived. Optical pulses will be transmitted to pulsed laser and BAM clients over stabilized fiber-optic links whereas the RF signals are transmitted over newly developed stabilized cw fiber-optic links. Both s- and cband reference signals use s-band links, whereupon the C band receiver incorporates an additional ultra-low jitter/drift frequency doubler. Furthermore, ultra-low noise analog laser PLLs have been built. We are presenting concepts and first results of sub-10fsrms jitter and 20fspp long term drift cw links, tested in the SwissFEL Injector Test Facility (SITF).

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.

"Probing the Transition State Region in Catalytic CO Oxidation on Ru" data files

Abstract: Catching CO oxidation Details of the transition state that forms as carbon monoxide (CO) adsorbed on a ruthenium surface is oxidized to CO2 have been revealed by ultrafast excitation and probe methods. Öström et al. initiated the reaction between CO and adsorbed oxygen atoms with laser pulses that rapidly heated the surface and then probed the changes in electronic structure with oxygen x-ray absorption spectroscopy. They observed transition-state configurations that are consistent with density functional theory and a quantum oscillator model. Science, this issue p. 978 Ultrafast x-ray spectroscopy reveals electronic changes that occur during the oxidation of carbon monoxide on a ruthenium surface. Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the O K-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC–O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.

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.