Fig. 1. High-regular one-dimensional periodic ripple structures obtained on several metal surfaces using linearly polarized single-beam femtosecond laser incidence. (a) 1 μm chromium film^[89]; (b) 50 nm titanium film^[90]; (c) 300 nm molybdenum film^[91]

Fig. 2. Highly regular one-dimensional periodic ripple structures on 25 nm Cr film by linearly polarized single-beam femtosecond laser beam under vacuum condition of 1.0×10^-4 Pa^[92]. (a) Focusing with a convex lens; (b) focusing with a cylindrical lens

Fig. 3. Large-area high-regular one-dimensional periodic ripple structures formed on tungsten surface using temporally delayed double femtosecond laser beams with orthogonal polarizations. (a) Structural morphology; (b) calcualted dispersion δθ in the structure orientation angle

Fig. 4. One-dimensional subwavelength periodic ripple structures formed on Molybdenum surface using temporally delayed double femtosecond laser beams with different wavelengths^[93]. (a)(b) Structural morphology at the time delay of Dt=10 ps andDt=100 ps, respectively; (c) variation of the structure period as function of the time delay between double laser beams

Fig. 5. Temporal evolution of the subwavelength periodic ripple structures formed on copper surface using temporally delayed double femtosecond laser beams with the polarization intersection angle of θ=45°^[95]. (a) Structural morphology at zero time delay incidence; (b) measured time-delay dependent slantwise orientation angle of the structures

Fig. 6. Temporal evolution of the subwavelength periodic ripple structures formed on 4H-SiC surface using temporally delayed double femtosecond laser beams with the polarization intersection angle of θ=30°^[96-97]. (a) Structural morphology at zero time delay incidence; (b) measured time-delay dependent slantwise orientation angle of the structures

Fig. 7. Temporal evolution of the subwavelength periodic ripple structures formed on 4H-SiC surface using temporally delayed three femtosecond laser beams with the polarization intersection angles of θ₁=θ₂=30°^[98]. (a) Structural morphology at Δt₁=10 ps and Δt₂=42 ps; (b)(c) measured time-delay dependent slantwise orientation angle of the structures at Δt₁=10 ps and

Fig. 8. Various types of two-dimensional periodic structure arrays on tungsten surface using temporally delayed double femtosecond laser beams with orthogonal polarizations. (a) Spherical cap^[100]; (b) triangular^[101]; (c) rhombus^[99]

Fig. 9. Two-dimensional elliptical-shaped periodic structure arrays formed on molybdenum surface using temporally delayed two-color femtosecond laser beams with orthogonal polarizations^[102]. (a) Surface morphology; (b)(c) measured time-delay dependent structure period in the vertical and horizontal directions, respectively

Fig. 10. Two-dimensional subwavelength ripple-particle hybrid structures formed on the copper surfaces using different femtosecond lasers[103