The subject of this work is the design implementation and first results of the CERN Resonant
WISP Search (CROWS) which probes the existence of Axion Like Particles and Hidden Sector
Photons (HSPs) using microwave techniques. By exploiting low loss cavity resonators multiple
layers of electromagnetic shielding and a micro-Hz bandwidth detection scheme new exclusion
limits could be set. For HSPs sensitivity was improved by a factor of ~7 compared to previous
laboratory experiments.
