We report optical evidence of cesium (Cs) evaporation from a bialkali (SbKCs) photo-cathode during controlled heating of a photomultiplier tube (PMT). A DFB laser scanned across the 852.113 nm Cs D2 line reveals absorption features only above 60 degrees Celsius, indicating thermal desorption. The absorption correlates with temperature and offers a non-invasive method to monitor photocathode degradation in sealed detectors.
@article{arxiv.2509.13168,
title = {Thermal Cesium Release in PMTs Revealed by Resonant Laser Spectroscopy and Its Correlation with Quantum Efficiency},
author = {Antonio De Benedittis and Pasquale Migliozzi and Carlos Maximiliano Mollo and Andreino Simonelli},
journal= {arXiv preprint arXiv:2509.13168},
year = {2025}
}