High-Precision Vertical Linear Translation for Offset Mirrors

The horizontal and vertical offset mirrors are key optical elements for the SwissFEL ARAMIS Beamline. The offset mirrors for example, are used to deflect and steer the x-ray beam into one of the end stations. As the sample position is about 60m from the mirror, very high demands are put on the mirror positioning system in order to deflect the x-ray beam on to the sample with a micro-meter precision. Therefore precise positioning of the mirrors is required, with specifications to move a load of up to 200kg by steps as small as 0.3µm. Not just the positioning must be precise, but also the stability for short term vibrations and long term drifts must be superior. Based on an original design from the Swiss Light Source which was further developed at Petra III at DESY, a third generation high-precision vertical linear stage has been designed at PSI. The fabrication and assembly was made at Högg AG Produktionstechnik in Wattwil, Switzerland. Extensive measurements were performed to ensure the design specifications. The full-range absolute position actuary has been determined to be better than 1.5µm, the uni-directional reproducibility is better than +/-0.2µm. All design specification could be met and were even exceeded in most cases.