Photon Sources at Uppsala University

The following is a review of photon sources at Uppsala University.

HELIOS

The Department of Physics and Astronomy operates a central facility (Helios) dedicated to providing femtosecond optical and vacuum ultraviolet pulses to Uppsala University groups.

Present capabilities

HELIOS (https://www.physics.uu.se/research/molcond/ongoingresearch/x-ray-based-methodology/helios/) is an HHG source optimized for very short pulses (<40 fs) at comparably high photon energies of 60-80 eV. Accessing shallow core levels at 60-80 eV is ideally suited for ultrafast element-specific studies in magnetization and chemical dynamics by access to M absorption edges of 3d transition-metals and the M/N edges of Se, Br, I. Pulse durations of <40 fs are essential for state-of-the-art chemical and magnetization dynamic studies (see, e.g., the time scale of molecular excited-state dynamics of 100 fs).

Future upgrades

We aim to extend the suite of complementary ultrafast x-ray facilities with new capabilities for time-resolved x-ray spectroscopy that will enable a broad range of scientific applications at the department. We plan to develop and use lab-based high-harmonic generation (HHG) to produce overtone harmonics of the femtosecond optical lasers over a wide extended ultraviolet (XUV) and soft x-ray spectral range. We aim to realize two facilities: One optimized for ultrafast element-specific x-ray spectroscopy with short pulses at the existing HELIOS laboratory and one optimized for time- and angle-resolved photoemission spectroscopy with small spectral bandwidth at the FREIA laboratory. This necessitates the installation of two new femtosecond optical laser systems (laser systems I and II) that we apply for here and we will provide matching funds to add installations to realize the described facilities.

Spectral and temporal resolution as well as pulse energy and repetition rate of an HHG x-ray source are determined by the properties of the driving femtosecond optical laser system. High spectral and temporal resolutions cannot be combined in one source due to the limitations imposed by the Fourier transform limit. Current laser technology limits the average power (pulse energy times repetition rate) of ultrafast lasers to 10-100 W. This prevents having both, high peak power (high pulse energy) and high average power. The two application fields of ultrafast element-specific studies and time-resolved ARPES therefore require very different driving laser systems. Element-specific studies require high peak power at moderate repetition rates and short pulses (laser system I with pulse energies of several mJ and repetition rates of few kHz). ARPES requires high average power (low peak power) at high repetition rates with longer pulses (laser system II with several 0.1 mJ pulses at several 100 kHz repetition rates).

At HELIOS, a new laser system will be used to generate XUV photon energies above the current 60 eV up to 200-300 eV, matching the core-level energies of a range of elements relevant in ultrafast chemistry, photocatalysis, and energy research. This will enable new time-resolved core-level studies of hitherto inaccessible classes of materials such as perovskite solar cells or organic systems in solution. A second Laser system will be the core of a new facility optimized for time-resolved ARPES at FREIA with an XUV spectral bandwidth of <20 meV, matching the excitation energies of elementary particles (charges, spins, phonons and magnons). This will enable state-of-the-art ARPES with exceptional spectral resolution and femtosecond temporal resolution for ultrafast materials science.

Small Angle X-ray Scattering

Xeuss 2.0

Combined small- and wide-angle x-ray scattering system (SAXS/WAXS) suitable for micro-structural characterization of systems containing nanoparticles, amphiphilic self-assemblies, microemulsions, emulsions, liquid crystalline phases, proteins and peptides, polymers, fibers, and thin solid films with characteristic length scales between 0.2 nm and 300 nm (USAXS: 5 µm).

The system is equipped with a high flux x-ray source, point collimation system, 2D detector, flexible control system and basic data reduction software.

The system provides high angular resolution data in a wide q-range and absolute intensity measurements.

The sample stage/environment can handle many different types of samples including liquids, pastes, gels and solids, in a wide temperature range. It is equipped with a low-noise flow-through cell for liquids. Samples can be investigated in vacuum or under ambient pressure.

Technical specifications

  • Instrument: Xeuss 2.0 Q-Xoom, equipped with Bonse-Hart ultra small-angle X-ray scattering analyser.
  • X-ray source: Microfocus sealed tube GeniX 3D (Cu, 30 W).
  • Flux at sample: > 450 Mph/s.
  • Detectors: 1) Pilatus3 R 300K 2D. Sensitive area: 84×106mm2. Pixel size: 172×172 µm2. Resolution: Δq=0.0028nm-1 at sample to detector distance 2.5 m. 2) Pilatus 100K for simultaneous SAXS/WAXS acquisition.
  • Sample-detector distances: 80 mm - 2.5 m (motorized movable detector system).
  • Available q-ranges: SAXS/WAXS: 0.025 - 41 nm-1; with USAXS extension: > 0.0012 nm-1.

For more information please contact Per Hansson, Pharmaceutical Physical Chemistry group, Department of Medicinal Chemistry, BMC, Uppsala University.

Last modified: 2021-03-12