Fig. 1. Theoretical analysis based on linewidth model. (a) Distribution of two-photon excited spot; (b) distribution of doughnut inhibition spot; (c) distribution of excitation light energy at focal plane and its Gaussian fitting function; (d) lateral profile of doughnut dark spot at focal plane and its parabolic fitting function; (e) simulated curve of lateral linewidth versus excitation power; (f) simulated curve of lateral linewidth versus inhibition power at fixed excitation power

Fig. 2. Schematic of PPI laser direct writing lithography system . (a) Optical path; measurement results of (b) excitation light and (c) inhibition light point spread functions at focal plane

Fig. 3. Format of control data used in system

Fig. 4. Flow chart of system control

Fig. 5. Polymerized line-arrays obtained by processing and attached on substrate. (a) With inhibition　light; (b) without inhibition light

Fig. 6. Fabrication results of suspended lines. (a)Structure of suspended lines; (b) feature size of suspended lines versus inhibition laser power under same excitation power where error bars represent standard deviation, and number of measurements is 5; (c) feature size of 134 nm without inhibition light [corresponding to point c in Fig. (b)]; (d) feature size of 30 nm with 13.6 mW inhibition light [corresponding to point d in Fig. (b)]

Fig. 7. Fabrication of complex graphic structures. (a) Two-dimensional array of cuboid units; (b) partial enlargement of Fig. (a); (c) pentagonal prisms; (d) two-dimensional array of spatial helix units; (e) partial enlargement of Fig. (d); (f) emblem of Zhejiang University; (g) line of large-sized equidistant Archimedes helix; (h) partial enlargement of Fig. (g); (i) three-dimensional flower-shaped structure