Metrology with synchrotron radiation at PTB

The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany and has been using synchrotron radiation (SR) for more than 40 years. Starting at the former facility BESSY I, the storage ring BESSY II (see corresponding article in this volume) has been used for this purpose since 1998, especially in the X-ray range, as well as PTB's own metrology light source (MLS) for lower photon energies since 2008. Both facilities are located in Berlin-Adlershof and are operated by the Helmholtz-Zentrum Berlin within the framework of contractual agreements with PTB. The basic motivation of the work is radiometry. The two storage rings MLS and BESSY II are used as primary source standards and cryogenic radiometers as primary detector standards. The article gives a brief overview of the present status, scientific highlights, the technological development and upgrade plans for the decade 2023-2033 as well as a perspective of next scientific challenges.