Powell lens is used to generate straight line. With aspherical curvature on its apex, the output line from powell lenses is even distribution of energy. For comparision, Cylindrical lenses generate gaussian beam profiles with hot-spot centre points and fading edges.
The uniformity of output line is also related with incident wavelength, beam size, divergence, and working distance.
To get even distribution of energy, The apex curvature need to be slightly modified and optimized for particular laser beam.