Internal modification in transparent hybrid germanium-silica plates using plasma formation induced by a femtosecond laser

The fabrication of an internal diffraction grating with photoinduced refractive index modification in planar hybrid germanium-silica plates was demonstrated using low-density plasma formation excited by a high-intensity femtosecond (150 fs) Ti: sapphire laser (λp=790 nm). The refractive index modifications with diameters ranging from 400 nm to 3 μm were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than 2×1013 W/cm2. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.