Optically tunable diffraction efficiency by photo-mobile holographic composite polymer material

We report on the fabrication and optical characterization of one-dimensional transmission holographic volume phase gratings written on a novel holographic composite mixture. The mixture is derived from a recently developed photo-mobile polymeric composite material. The transmission gratings recorded on the photo-mobile film are constituted by polymeric walls and low viscous inter-walls material. Using an external pumping laser operating at lambda = 457.9 nm the transmission efficiency linearly increases with the laser power and, in our range of power values, the phenomenon is completely reversible. At highest power level a 30% diffraction efficiency is achieved. The increase of the diffraction efficiency is related to the increase of the refractive index contrast of the grating mixture. In particular, under illumination, the low viscous material escapes from the irradiated area. This feature could explain the experimentally observed changes of the refractive index contrast.