Conversion of a Gaussian-distributed circular beam to a flat-top-distributed square beam in laser shock processing based on a micro-lens array structure

A novel beam homogenisation system based on a micro-lens array and beam expansion structure is proposed to convert a Gaussian-distributed circular beam to a flat-top-distributed square beam of size 2–5 mm and a homogeneity degree exceeding 95%. The novel micro-lens array based on a cylindrical lens element can potentially be widely applied in practice because of the absence of the preparative limitations of size and focal length. By employing this beam homogenisation system, laser shock processing experiments were performed on 7050 titanium alloy. The laser shock processing parameters were optimised. When the laser repetition frequency was 1 Hz, pulse width was 15 ns, and laser energy was 20 J, a residual stress of > 400 MPa was achieved on the titanium alloy. The experimental results demonstrate the ability of this beam-homogenisation system to perform laser shock processing.