Phase-locked MHz pulse selector for x-ray sources

• Published in: Optics letters 2015-05, Vol.40 (10), p.2265-2268
• Main Authors: Förster, Daniel F, Lindenau, Bernd, Leyendecker, Marko, Janssen, Franz, Winkler, Carsten, Schumann, Frank O, Kirschner, Jürgen, Holldack, Karsten, Föhlisch, Alexander
• Format: Article
• Language: English
• Subjects: Choppers; Purity; Repetition; Selectors; Slits; Wheels; X-ray sources; X-rays
• ISSN: 0146-9592; 1539-4794
• DOI: 10.1364/OL.40.002265

Picosecond x-ray pulses are extracted with a phase-locked x-ray pulse selector at 1.25 MHz repetition rate from the pulse trains of the accelerator-driven multiuser x-ray source BESSY II preserving the peak brilliance at high pulse purity. The system consists of a specially designed in-vacuum chopper wheel rotating with ≈1  kHz angular frequency. The wheel is driven in an ultrahigh vacuum and is levitated on magnetic bearings being capable of withstanding high centrifugal forces. Pulses are picked by 1252 high-precision slits of 70 μm width on the outer rim of the wheel corresponding to a temporal opening window of the chopper of 70 ns. We demonstrate how the electronic phase stabilization of ±2  ns together with an arrival time jitter of the individual slits of the same order of magnitude allows us to pick short single bunch x-ray pulses out of a 200 ns ion clearing gap in a multibunch pulse train as emitted from a synchrotron facility at 1.25 MHz repetition rate with a pulse purity below the shot noise detection limit. The approach is applicable to any high-repetition pulsed radiation source, in particular in the x-ray spectral range up to 10 keV. The opening window in a real x-ray beamline, its stability, as well as the limits of mechanical pulse picking techniques in the MHz range are discussed.