Investigation of readout methods for electro-optical beam position monitor pickups

Electro-optical pickups are being explored at CERN for the development of a high-bandwidth beam position monitor capable of measuring intrabunch beam position. To support this effort, a prototype electro-optical beam position monitor has been installed in the SPS. The installation utilises a fibre-coupled laser directed into lithium niobate crystals. As the beam passes a crystal, its electromagnetic field induces a proportional phase shift in the laser light by altering the crystal’s refractive index. Signal readout is typically performed using a Mach-Zehnder interferometric setup, with crystals placed on either side of the beam. This configuration currently faces challenges including imperfect pickup matching, baseline instability, and limited dynamic range. This paper examines and evaluates various methods and techniques for reading out the beam position from the phase-shifted laser to mitigate these limitations.