Fig. 1. (a) Experimental setup used for processing LSFL on silicon with a temporally shaped femtosecond laser. (b) Periodic π-phase step modulation applied to the laser spectrum. (c) Temporal intensity profile of the shaped pulse of 16.2 ps with a modulation period of 4.5  cm−1.

Fig. 2. Schematic diagram of shaped pulse laser-induced regular and deep LSFL. The red area in the Si substrate presents the high temperature region when the sub-pulse reaches the surface.

Fig. 3. (a)–(d) SEM images of LSFL fabricated by shaped pulse of 16.2 ps through laser direct writing in parallel lines. (e) SEM image of the cross section of the LSFL. (f) 2D-FFT image of (b). (g) Spectrum of the FFT along the x axis. The scale bar in (e) is 500 nm long. The dash arrow in (a) presents the laser polarization, and the solid arrow presents the scan direction.

Fig. 4. (a) Optical characterization measurement for testing the diffractive properties of large-area LSFL. The diffraction spectra from the LSFL fabricated (b) by shaped pulse of 16.2 ps and (c) by FTL pulse. The orderly multicolor diffraction pattern from the LSFL fabricated (d) by shaped pulse of 16.2 ps and (e) by FTL pulse.

Fig. 5. Structural colors of “Chinese knot” pattern made up of LSFL fabricated by shaped pulse of 16.2 ps on Si surface. The white scale bars are 5 mm long.

Fig. 6. (a) At different scan velocity, the laser fluence windows for fabricating spaced (green), regular (orange), and partly damaged (blue) LSFLs by shaped pulse of 16.2 ps (the upper area) and by FTL pulse (the lower area). The SEM images (s1)–(s6) and (f1)–(f6) are the corresponding LSFLs of the marked points in (a). The dash arrow in (s1) presents the laser polarization, and the solid arrow presents the scan direction. The scale bars have a length of 3 μm.

Fig. 7. Confocal microscopy images of the regular LSFL fabricated by (a) FTL pulse (F=0.43  J/cm2) and (b) shaped pulse of 16.2 ps (F=0.69  J/cm2). The scan velocity is 5.0 mm/s. (c) and (d) 2D plots of the cross sections along the yellow arrows in (a) and (b), respectively. (e) Average depth of the LSFL along the cross section perpendicular to the ablation trace.

Fig. 8. SEM images of the surface nanostructures fabricated by FTL pulse at different scanning velocities of (a) 16 mm/s, (b) 14 mm/s, (c) 10 mm/s, and (d) 8 mm/s. The laser fluence was fixed at 0.54  J/cm2. The dashed arrow presents the laser polarization, and the solid arrow presents the scanning direction. The scale bars are all 5 μm in length.

Fig. 9. SEM images of the surface nanostructures fabricated by shape pulse of 16.2 ps at different scanning velocities of (a) 17 mm/s, (b) 15 mm/s, (c) 13 mm/s, and (d) 11 mm/s. The laser fluence was fixed at 1.13  J/cm2. The dashed arrow presents the laser polarization, and the solid arrow presents the scanning direction. The scale bars are all 5 μm long.

Fig. 10. Confocal optical images of LSFL fabricated by shaped pulse of (a) 16.2 ps, 0.65  J/cm2; (b) 4.1 ps, 0.44  J/cm2; (c) 1.0 ps, 0.43  J/cm2; and (d) 0.25 ps, 0.42  J/cm2. The scan velocity was fixed as 5 mm/s. (e) The period and depth of the LSFLs for different intervals of sub-pulse.

Fig. 11. Evolution of (a) the carrier density, (b) the carrier temperature, (c) the lattice temperature, and (d) the real part of the dielectric constant on the Si surface irradiated with shaped pulse of 16.2 ps.