We experimentally extend the nonlinear Gaussian to flattop beam shaping from one to two dimensions through a three-dimensional nonlinear photonic crystal. Employing a near -infrared femtosecond laser, we induce a modification inside lithium niobate to achieve a second -order nonlinear optical coefficient modulation in three dimensions. The flat-topped truncation of wavefront has been adjusted in a mutual perpendicular coordinate separately. Among the generated flat-topped beams, the optimal flatness is 97.1%, and the nonlinear conversion efficiency is 10-2 at the peak power of 37 kW with the i...
