Detection of Moisture in Oil Using Evanescent Absorption from Sapphire Optical Waveguide Coated with Co-Doped Silica Film

We present a device that facilitates the measurement of moisture in oil or organic solvents. The device exploits the absorption of the evanescent waves from an optical waveguide to measure changes in the absorption spectra of CoCl2-doped thin films on sapphire. We fabricate a thin film from silica sol solution and find that the addition of Triton-X 100 facilitates the fabrication of a water-sensitive film. We discuss the conditions for adding Triton-X 100 and for the heat treatment and report on the state of the thin film from measurements using a DIC microscope, powder XRD, and a SEM.