Gas detectors for x-ray lasers

TLDR

The authors optimized low‑density gas photodetectors for shot‑to‑shot photon diagnostics at XFELs, achieving sub‑100‑ns temporal resolution, and calibrated them at BESSY II, with a hard‑X‑ray upgrade tested at Stanford’s Sub‑Picosecond Photon Source. The devices, based on gas photoionization, achieve <10 % uncertainty in photon‑pulse energy and <20 μm uncertainty in beam position at FLASH.

Abstract

We have developed different types of photodetectors that are based on the photoionization of a gas at a low target density. The almost transparent devices were optimized and tested for online photon diagnostics at current and future x-ray free-electron laser facilities on a shot-to-shot basis with a temporal resolution of better than 100 ns. Characterization and calibration measurements were performed in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin. As a result, measurement uncertainties of better than 10% for the photon-pulse energy and below 20 μm for the photon-beam position were achieved at the Free-electron LASer in Hamburg (FLASH). An upgrade for the detection of hard x-rays was tested at the Sub-Picosecond Photon Source in Stanford.