Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n+ region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

Due to their high frame rates and dynamic range, large area coverage, and high signal-to-noise ratio, hybrid silicon pixel detectors are an established standard for photon science applications at X-ray energies between 2 keV and 20 keV. These properties also make hybrid detectors interesting for experiments with soft X-rays between 200 eV and 2 keV. In this energy range, however, standard hybrid detectors are limited by the quantum efficiency of the sensor and the noise of the readout electronics. These limitations can be overcome by utilizing inverse Low-Gain Avalanche Diode (iLGAD) sensors with an optimized X-ray entrance window. We have developed and characterized a prototype soft X-ray iLGAD sensor bonded to the charge integrating 75 µm pixel JUNGFRAU chip. Cooled to −22°C, the system multiplication factor of the signal generated by an impinging photon is ≥ 11. With this gain, the effective equivalent noise charge of the system is ≤5.5 electrons root-mean-square at a 5 µs integration time. We show that by cooling the system below −50°C, single photon resolution at 200 eV becomes feasible with a signal-to-noise ratio better than 5.

The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy, and ab initio molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The x-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the x-ray absorption signal is found to rise in ∼1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of ∼100 cm−1, which corresponds to a phonon mode of the system involving the Zn sub-lattice.

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-Å 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.

Providing a reliable and performant Data Acquisition System (DAQ) at Free Electron Lasers (FELs) is a challenging and complex task due to the inherent characteristics of a pulsed machine and consequent need of beam synchronous shot-to-shot DAQ, which enables correlation of collected data associated with each FEL pulse. We will focus on experiences gathered during the process of moving towards 100 Hz operation at SwissFEL from the perspective of beam synchronous DAQ. Given the scarce resources and challenging deadlines, many efforts went into managing conflicting stakeholder expectations and priorities and into allocation of time for operation support and maintenance tasks on one side and time for design and development tasks on the other side. The technical challenges we encountered have shown a great importance of having proper requirements in the early phase, a well thought system design concept (which considers all subsystems in the DAQ chain), and a well-defined test framework for validation of recorded beam synchronous data

Data acquisition software is an essential component of modern macromolecular crystallography (MX) beamlines, enabling efficient use of beam time at synchrotron facilities. Developed at the Paul Scherrer Institute, the DA+ data acquisition software is implemented at all three Swiss Light Source (SLS) MX beamlines. DA+ consists of distributed services and components written in Python and Java, which communicate via messaging and streaming technologies. The major components of DA+ are the user interface, acquisition engine, online processing and database. Immediate data quality feedback is achieved with distributed automatic data analysis routines. The software architecture enables exploration of the full potential of the latest instrumentation at the SLS MX beamlines, such as the SmarGon goniometer and the EIGER X 16M detector, and development of new data collection methods.

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.

We have performed femtosecond X-ray spectroscopy measurements after UV photoexcitation of a colloidal solution of ZnO nanoparticles. The results indicate sub-ps hole trapping at oxygen vacancies with shallowly-trapped electrons in the conduction band.

A fast continuous grid scan protocol has been incorporated into the Swiss Light Source (SLS) data acquisition and analysis software suite on the macromolecular crystallography (MX) beamlines. Its combination with fast readout single-photon counting hybrid pixel array detectors (PILATUS and EIGER) allows for diffraction-based identification of crystal diffraction hotspots and the location and centering of membrane protein microcrystals in the lipid cubic phase (LCP) inin meso in situserial crystallography plates and silicon nitride supports. Diffraction-based continuous grid scans with both still and oscillation images are supported. Examples that include a grid scan of a large (50 nl) LCP bolus and analysis of the resulting diffraction images are presented. Scanning transmission X-ray microscopy (STXM) complements and benefits from fast grid scanning. STXM has been demonstrated at the SLS beamline X06SA for near-zero-dose detection of protein crystals mounted on different types of sample supports at room and cryogenic temperatures. Flash-cooled crystals in nylon loops were successfully identified in differential and integrated phase images. Crystals of just 10 µm thickness were visible in integrated phase images using data collected with the EIGER detector. STXM offers a truly low-dose method for locating crystals on solid supports prior to diffraction data collection at both synchrotron microfocusing and free-electron laser X-ray facilities.

The design and performance of the new multi-axis goniometer PRIGo developed at the Swiss Light Source at Paul Scherrer Institute is described.

The three macromolecular crystallography (MX) beamlines at the Swiss Light Source (SLS) rank among the most productive in Europe. The very successful design of the first beamline, X06SA, inaugurated in 2001, was the basis for the second beamline, X10SA, operated by the Paul Scherrer Institut and financed by the partners Max Planck Society, Novartis and Hofmann-La Roche. To keep up with the increasing demand for high throughput crystallographic experiments, especially in an industrial environment, as well as the rising interest in more challenging targets, the beamline is under constant development. Here we will present the recent advances in usability and performance, including software integration and automation with the completely new data acquisition software DA+, in-situ screening for diffraction candidates, (serial) micro-crystallography with micro-beam, and beamline hardware.