Beamline Instrumentation: Compact Linear Stage Positions X-Ray Detectors for Analyzing the Interactions of FEL Synchrotron Radiation with Matter

Physik Instrumente (PI): Benefitting research: A linear stage from PI miCos enables scientists to study phenomena in molecular physics in the femtosecond range. Requirements are quite demanding here: Components for an experiment setup with intensive X-ray laser pulses have to be tuned accordingly.

A new experiment is currently being set up at the Atomic, Molecular & Optical Science Beamline (AMO) of the Linac Coherent Light Source (LCLS), part of the SLAC (Stanford Linear Accelerator Center); its purpose is to give insight into the interaction of FEL synchrotron radiation with atoms, molecules and clusters.

The LCLS is a free-electron laser source (FEL) and produces synchrotron radiation of extremely high brilliance. It emits a radiation of 0.15 nm wavelength with pulses in the femtosecond range. With its radiation, a wide range of new experiments can be effected, e.g. in nonlinear X-ray physics and for single-shot imaging of nanometer structures. Using this technology, scientists can, for example, trace the movement and position of atoms within one complex molecule.

Reactions that are triggered by laser radiation in the sample are examined using electron and ion spectroscopies or X-ray diffraction. "For simultaneously recording scattered X-ray photons on the one hand, and ions and electrons from the interaction of the intense X-ray pulses with the sample on the other hand, a pnCCD camera, which is a highly sensitive X-ray camera, has to be positioned very precisely and with highest repeatability", explains Christoph Bostedt, Senior Staff Scientist at LCLS. The camera records an entire spectrum on one pixel at very high frame rates of 1000 images per second. Due to the parallel architecture of the detector, the main laser beam can pass between the detector parts without damaging them.

Precisely Tuned to X-Ray Scattering

For positioning the two detectors, PI miCos developed a compact linear stage that features a guiding and two separate moving plates. The detectors are able to move independently over a travel range of 50 mm. They touch each other in the 0 "closed" position; the maximum distance between the detectors is 100 mm. The motion of the platforms is controlled by an absolute measuring linear encoder with 50 nm resolution.

When positioning both detectors accordingly, the scattered X-ray beams can be recorded at a wide angle range and can be evaluated spatially and spectrally.
The linear stage is designed for ultrahigh vacuum to 10-9 hPa and is made of stainless steel.

PI miCos in Brief
The miCos GmbH was founded in Eschbach near Freiburg, Germany, in 1990. As PI miCos, it now belongs to PI Group (Physik Instrumente), located in Karlsruhe, Germany. With currently more than 50 employees, the company develops, produces and markets innovative motion systems and components for high-precision positioning applications throughout the world. A main focus is on optical metrology in research and industry. For this purpose, PI miCos offers customized system solutions with multiple axes in addition to a comprehensive standard program. Wide-ranging application know-how guarantees the implementation of technically demanding solutions. Flexible positioning systems for ultrahigh vacuum applications are a good example of this, as are parallel-kinematic Hexapods with six degrees of freedom and systems with air bearing axes for highest running accuracy.