Illumination technique for the relative calibration of the ASTRI SST-2M camera

We present a new illumination technique for the camera relative gain calibration of the ASTRI SST-2M Cherenkov telescope. The camera illumination is achieved by means of an optical fiber that diffuses the light inside a protective PMMA window above the focal plane. We report the encouraging results of the development tests carried out on two PMMA window prototypes illuminated by a standard optical fiber. We checked also the reliability of the method by a series of ray tracing simulations for different scattering models and PMMA window shapes finding good agreement with experimental results.