Luis C. Reyes
Gamma rays with energy above 10 GeV interact via pair-production with low-energy photons from the Extragalactic Background Light (EBL). This results in a redshift- and energy-dependent attenuation of the Gamma-ray flux of extragalactic sources like blazars and Gamma-ray bursts. The Fermi Large Area Telescope (LAT) is providing us with a rich sample of Gamma-ray blazars with redshifts up to z~3 that we have used to probe this phenomena. In this contribution we will present the opacity limits obtained after one year of Fermi observations and how they compare to the values predicted by well-known EBL models.