Fig. 1. (a) Confocal optical microscopy image of LSFL prefabricated on silicon surface, and (b) cross-sectional profile of LSFL.

Fig. 2. (a) Experiment setup of the collinear pump-probe imaging system; HWP is half wave plate, PBS is polarized beam splitter, and BS is beam splitter. (b) Spectra of the white-light pulse with (red solid curve) and without (black dotted curve) the short-wave-pass filter. (c) Laser spot area on the object plane with and without the concave lens. (d) The profile of the normalized intensity of blue light emission and laser field intensity along the arrow in (c).

Fig. 3. Optical images of surface microstructures before (a) and after (b–c) irradiation by a single laser pulse.

Fig. 4. Optical micrographs of the silicon surface at different delay times after single-pulse laser irradiation. The horizontal double arrow shows the laser polarization direction.

Fig. 5. Two-dimensional FT images of the surface nanostructures shown in Fig. 4 at different delay times. (a) 100 ps, (b) 250 ps, (c) 700 ps, and (d) 850 ps, respectively. (e) The FT spectra in the x-direction of K_y=0.

Fig. 6. The delay time dependence of the peak intensity ratio of HSFL to LSFL corresponding to the FT images.

Fig. 7. Optical micrographs of the silicon surface with pre-fabricated LSFL at different delay times after irradiation by a single laser pulse with different fluences. (a–e) Laser fluence is 0.44 J/cm², (f–j) is 0.59 J/cm², (k–o) is 1.76 J/cm², and (p–t) is 3.53 J/cm². The red horizontal double arrow shows the laser polarization direction. The gray scale in all figures is 3 microns.

Fig. 8. Evolution of surface morphology with delay time under single pulse irradiation with different laser fluences. LSFL was pre-fabricated prior to irradiation by a single pulse.

Fig. 9. The laser fluence dependence of the period of uniform and clear HSFL under femtosecond laser irradiation.

Fig. 10. (a–c) Schematic diagram of the formation process of submerged nanocavities during LSFL prefabrication. (d–f) Schematic diagram of the formation of uniform HSFL.

Fig. 11. SEM images of the LSFL prefabricated on a silicon surface by direct writing with dual-beam interference, where a single-beam laser with a fluence of 0.13 J/cm² and a scanning speed of 2 mm/s. (a–b) Before etched, and (c–f) after etched with HF solution.

Fig. 12. SEM image of silicon surface by direct writing with dual-beam interference, where a single-beam laser with a fluence of 0.24 J/cm² and a scanning speed of 2.0 mm/s. The sample was not corroded with HF solution.