Fiber Optic Sensors for Relative Humidity Monitoring in High Energy Physics Applications

In this contribution we present investigations developed in the last years by our multidisciplinary research group concerning the use of fiber grating based sensors for relative humidity monitoring in the Compact Muon Solenoid (CMS) experiment at CERN, in Geneva. In particular our research, firstly focused on the development of polyimide coated Fiber Bragg Grating sensors, has been recently extended to Long Period Grating sensors, coated with a finely tuned titanium dioxide (TiO2) thin layer (similar to 100 nm thick). Experimental tests in [0-75] %RH range at different temperatures were carried out to assess the sensors' performances in conditions required in experiments running at CERN. Progressive irradiation campaigns with gamma- ionizing radiations were also performed. Obtained results demonstrate the strong potentialities of the proposed technologies in light of their future exploitation as robust and valid alternative to currently used commercial hygrometers in High Energy Physics (HEP) applications.