Femtosecond laser two-photon polymerization (TPP) is a potential method for 3D microstructure fabrication. The conventional direct writing TPP has high spatial resolution due to point-by-point scanning but usually time-consuming, thus it is difficult to fabricate large-volume microstructures or arrays. Here, we demonstrate the rapid femtosecond laser TPP of arbitrary 3D microstructures with 3D focal field engineering (FFE) by inversely retrieving the incident beam profile from the target focal field, which pave the way for rapid polymerization of large-scale microstructures. Moreover, annealing as post heat treatment provides an approach using the thermal reflow to smoothen the surface.

For a relatively large 3D microstructure, the desired focal field is hard to be engineered directly or the required total energy is too strong to damage the optical components during TPP. Therefore, we engineer the focal field intensity distribution into the slices of the whole microstructure. In this way, the microstructure is formed by continuous TPP with 1D scan of the corresponding 2D sliced intensity distribution. Furthermore, we adapt the constraints and the initial conditions of the Gerchberg– Saxton algorithm to ensure the smoothness of the focal field. When exposing, we upload the phase masks onto the spatial light modulator consecutively and move the XYZ-stage accordingly. It takes only 5 s to polymerize a Great Wall with the dimension of 29.2×15.2×9.2 microns divided into 146 slices via 3D FFE. The continuous surface Fresnel lens array is also fabricated by the femtosecond laser TPP with 3D FFE. Each lens with a diameter of 40 microns is polymerized within 7s. In addition, we anneal the lens array as post heat treatment to smoothen the lens surface.