Design of beam shaping and focusing metasurface device based on G-S algorithm

We demonstrate a sub-diffraction flat-top beam shaping device based on sub-wavelength square silicon pillar array at operating wavelength of 10.6 mu m, followed with improved Gerchberg-Saxton (G-S) algorithm to enable the advanced shaping processing capability. The theoretical simulation results show that the device generates a sub-diffraction flat-top optical needle with length of 10.6 cm along the optic axis, and its diffraction efficiency is higher than 90%. Moreover, the focal spot, with a transverse size of 3.5 lambda, is smaller than the diffraction limit of 6.8 lambda. This sub-diffraction beam shaping device with large focal depth has practical applications in laser machining technologies.