Fig. 1. Concept of femtosecond-laser-induced reshaping of Al nanodiscs and the curvature-driven diffusion model. (a) Schematic of surface diffusion of Al discs in an MIM configuration induced by fs pulses. The inserted arrows represent the curvature-driven surface atom migration. (b) The diameter and height of Al discs are d=130nm and h=30nm, respectively. The thicknesses of the SiO2 layer and the Ag layer are t₁=20nm and t₂=200nm, respectively. The Al nanodisc is arranged in a square lattice array with a periodicity p=300nm.

Fig. 2. (a) Electric field, magnetic field, and heat intensity distribution in the cross section of an Al nanodisc at 800 nm wavelength, respectively. (b) The simulated temperature evolution of Al nanodisc. The blue line represents the transient temperature of the disc after multi-pulse irradiation. (c) Temperature-dependent surface diffusion coefficients D_s(T) used for the theoretical fitting with Eq. (6) to the experimental data for a range of initial aspect ratios. (d) Simulated shape evolution of simplified model with an initial aspect ratio of 4.3 for various times showing the reshaping trajectory. (e) The diameter evolution of Al disc as a function of laser power. The right column is the SEM images of Al discs with different morphologies by increasing laser fluence. Scale bar: 150 nm.

Fig. 3. Reflecting spectra of Al nanodiscs and color palette. (a) Experimental and simulated reflecting spectra of Al discs after varying laser fluence. (b) Color palette. (c) The CIE1931 chromaticity coordinates of colors from the measured reflectance under white light illumination.

Fig. 4. (a)–(c) A collection of images printed by fs laser beams, showing the capability of high-resolution printing with high color fidelity. (d), (e) The SEM images and a zoom-in view of one section of the butterfly shown in (a). (f) The SEM images for comparison of Al discs before (right column) and after (left column) laser irradiation.