Power amplification in the core area of radial carpet beams

Abstract

We investigate the power redistribution in radial carpet beams (RCBs). We show that RCBs have increased power in the core area, which surrounds the central patternless area, as they propagate. We present both theoretical and experimental evidence that RCBs self-amplify in the core area due to their radial expansion. We examine the power carried by a main intensity spot of different RCBs produced by the diffraction of a plane wave from amplitude/phase radial gratings with sinusoidal/binary transmission profiles. We find that the core area, which has a complex intensity distribution, increases in power as the beam propagates. This feature distinguishes RCBs from other beams and makes them self-amplifying-like beams. Thus, the power amplification in RCBs is an internal effect caused by the continuous transfer of power from the patternless area to the core area. The power transfer to the core area also improves the stability of the beam in turbulent environments such as the atmosphere, making it a promising candidate for atmospheric optical communication. We discuss the practical realization of RCBs with a finite-radius beam and a radial grating. We define a “power amplification length” as the propagation distance at which the outer radius of the core area of the beam equals the beam radii at the grating. For instance, for the beam radii of 5 and 50 cm at the grating with 20 spokes, the values of these distances are 230 m and 23 km, respectively.