LIDAR (LIght Detection And Ranging) is an active remote sensing system that uses principles somewhat like the radar, but using a laser beam. The light atmosphere interaction yields optical fenomena that the system detect, measure and process. In agreement with the instrumental features both transmission and reception stages, can be to extract several atmospheric features like temperature profiles, density, concentration levels of particles and aerosols, pollution, ozone and others. Introducing to the theoretic concepts and the design of a basic system, and to end, an aproximation to the signals that would receive an actual LIDAR.