The main purpose of this paper is the design and simulation of a laser beam shaping system which can be used in a Free Space Optical (FSO) communication transmitter terminal prototype. It is known that a top-hat beam source is less affected from turbulence in the atmosphere than a Gaussian beam source. The design of a refraction beam shaper has been performed and verified in the optical design software ZEMAX. The paper also discusses the diffraction phenomenon which influences irradiance distribution of the beam.