Fig. 1. Yee cells in FDTD method

Fig. 2. Model structures. (a) 3D diagram of grating structure; (b) front view of grating structure; (c) top view of grating structure; (d) 3D diagram of rectangular array; (e) front view of rectangular array; (f) top view of rectangular array; (g) 3D diagram of pyramid array; (h) front view of pyramid array; (i) top view of pyramid array

Fig. 3. Simulation results of laser irradiation on rough iron surface. (a) Electromagnetic field energy distribution on surface; (b) FFT result of Fig. 3(a); (c) side view of Fig. 3(b)

Fig. 4. Simulation results of multiple laser irradiations on rough iron surface. (a) Electromagnetic field energy distribution on surface; (b) FFT result of Fig. 4(a); (c) side view of Fig. 4(b)

Fig. 5. Simulation results. (a) Electromagnetic field energy distribution and (b) XOZ interfaceelectromagnetic field energy distribution of grating with slot width of 700 nm and duty cycle of 50% on iron surface; (c) electromagnetic field energy distribution and (d) XOZ interface electromagnetic field energy distribution of grating with slot width of 900 nm and duty cycle of 50% on iron surface

Fig. 6. Simulation results under different slot widths. Electromagnetic energy distributions on material surfaces when slot widths are (a) 700, (c) 875, (e) 1050, (g) 1225, (i) 1400, and (k) 1575 nm; electromagnetic energy distributions on XOZ interfaces when slot widths are (b) 700, (d) 875, (f) 1050, (h) 1225, (j) 1400, and (l) 1575 nm

Fig. 7. Simulation results of single structural unit on surface of laser irradiated material. (a) Electromagnetic field energy distribution caused by single rectangular structure on iron plane and (b) electromagnetic field energy distribution on XOZ section; (c) electromagnetic field energy distribution caused by single pyramid structure on iron plane and (d) electromagnetic field energy distribution on XOZ section

Fig. 8. Simulation results. Energy distributions of electromagnetic fields on surfaces of iron rectangular arrays with X-axis periods of (a) 700, (c) 875, (e) 1050, (g) 1225, (i) 1400, and (k) 1575 nm; energy distributions of electromagnetic fields on XOZ interfaces of materials with X-axis periods of (b) 700, (d) 875, (f) 1050, (h) 1225, (j) 1400, and (l) 1575 nm

Fig. 9. Simulation results. Energy distributions of electromagnetic fields on material surfaces when X-axis period of iron array is 700 nm and Y-axis periods are (a) 0, (c) 200, (e) 350, (g) 500, (i) 700 nm; energy distributions of electromagnetic fields on YOZ interfaces when X-axis period of iron array is 700 nm and Y-axis periods are (b) 0, (d) 200, (f) 350, (h) 500, (j) 700 nm

Fig. 10. Simulation results. Energy distributions of interface electromagnetic fields for rectangular prefabricated structures with heights of (a) 30, (c) 50, (e) 100, and (g) 150 nm; energy distributions of XOZ interface electromagnetic fields for rectangular prefabricated structures with heights of (b) 30, (d) 50, (f) 100, and (h) 150 nm

Fig. 11. Simulation results. Energy distributions of electromagnetic fields on surfaces of iron materials with X-axis periods of (a) 700, (c) 875, (e) 1050, (g) 1225, (i) 1400, and (k) 1575 nm; energy distributions of electromagnetic fields on XOZ interfaces of iron materials with X-axis periods of (b) 700, (d) 875, (f) 1050, (h) 1225, (j) 1400, and (l) 1575 nm

Fig. 12. SPP coupling caused by vertical arrangement of multiple rectangular structures