Ultra-low-charge operation of free-electron lasers down to 1 pC or even lower, requires adequate diagnostics for both, the users and the operators. For the electro-optical bunch-arrival time monitor (BAM) a fundamental design update is necessary to yield single-digit fs precision with such low charges. In 2023 a vacuum sealed demonstrator for a novel pickup structure with integrated combination network on a printed circuit board (PCB) was built for operation at the free-electron laser ELBE at HZDR. Together with a new low-pi-voltage ultra-wideband traveling wave electro-optical modulator, this concept reaches an estimated theoretical jitter charge product of 9 fs pC. Proof-of-concept measurements with the pickup demonstrator were carried out at ELBE.

Ultra-low-charge operation of free-electron lasers down to 1 pC or even lower, requires adequate diagnostics for both, the users and the operators. For the electro-optical bunch-arrival time monitor (BAM) a fundamental design update is necessary to yield single-digit fs precision with such low charges. In 2023 a vacuum sealed demonstrator for a novel pickup structure with integrated combination network on a printed circuit board (PCB) was built for operation at the free-electron laser ELBE at HZDR. Together with a new low-pi-voltage ultra-wideband traveling wave electro-optical modulator, this concept reaches an estimated theoretical jitter charge product of 9 fs pC. Proof-of-concept measurements with the pickup demonstrator were carried out at ELBE.