Generation of a terahertz collimated top-hat beam by using two thin diffractive phase plates

We propose an efficient approach for shaping a terahertz (THz) Gaussian beam to a collimated top-hat beam by using two thin diffractive phase plates. The phase plates are designed based on the phase retrieve algorithm and fabricated by well-developed 3D-printing technology. The designed THz top-hat beam is experimentally realized at 0.3-THz. Both the calculated root mean square (RMS) uniformity and fraction of the total beam power of the output top-hat beam are over 80%, respectively. Additionally, the comparison between our approach and the traditional system containing of two refractive aspheric lenses is performed, showing that our beam shaping system has higher energy utilization.