Mechanism of hologram formation on glass surface by recording technique with corona discharge

Surface relief grating of azobenzene polymer formed on a soda-lime-silica glass plate was treated by corona discharge for the formation of a hologram on the glass plate. The Na concentration distribution near the glass surface was investigated using a time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth analysis with buckminsterfullerene (C60) ion sputtering and an image processing. The periodical Na deficient region identical to the azobenzene grating pattern existed near the glass surface, which suggested that the Na ions below the grating groove preferentially migrated to the cathode side during the corona discharge treatment. Generally, the refractive index of the Na poor region becomes lower than that of the pristine soda-lime silica glass. Therefore, the origin of the hologram on the glass surface should be the three-dimensional distribution of refractive index at the glass surface.