Needle Beam Generated by a Laser Beam Passing Through a Scattering Medium

The propagation of coherent light through an inhomogeneous medium generates a speckle pattern caused by the complex interference of randomly scattered waves. The speckle pattern does not resemble the incident beam profile. However, the spatially random pattern can be reshaped into a bright focal spot by wavefront shaping. And, in general, the focused intensity is of maximum just at the focal plane, and the focused intensity of the shaped focal beam decreases sharply with incremental distance from the focal plane. In this paper, we report the experimental generation of a needle beam as the laser beam passes through a scattering medium. The intensity and beam size of the needle beam remain nearly intact within the distance of 25 mm, which indicates that the focal pattern has a uniform property.