Experimental setup for investigation of laser beam propagation along horizontal urban path

It is well known that a laser beam propagating through optical atmosphere is affected by atmospheric turbulence. In this paper, we describe an experimental double-passage system for laser beam propagation along a horizontal urban path that can be useful for applications such as free-space laser communications. The setup includes a telescope to focus a laser beam on a retro-reflector, which is located 410 meters away, and the optical-test bench with which we measure intensity and phase fluctuations of the reflected beam. In our measurements scintillation is decreasing with distance from the center of the pupil. This shows the need for further theoretical modelling of double-passage systems.