Mirror-Assisted Radioluminescent Optical Fibers for X-Ray Beam Monitoring

In the framework of the current development of optical fiber (OF) sensors for dosimetry or beam monitoring applications based on radioluminescence (RL), we propose a method to enhance their radiation-induced light collection efficiency. This method consists of the deposition of a thin metallic layer, acting as a mirror, at the free output extremity of a radioluminescent OF. Emitted visible photons guided in both directions along the OF core can be collected by a single-ended detection system such as a photomultiplier tube (PMT). We characterize the impact of depositing two different types of metallic mirrors (Al and Au) on the performances of an RL-based dosimeter, constituted by nitrogen (N)-doped multimode OF: its sensitivity has been calibrated with 40 keV X-rays at room temperature for dose rates from 0.05 to
$\sim $
4 Gy(SiO2)/s. Also, an investigation of the total ionizing dose (TID) effects on the mirror has been carried out to understand the evolution of the reflectance of the mirror under radiation exposure. This architecture of sensors appears very promising, especially for the monitoring of low photon flux.