Fig. 1. Schematic of microscale laser shock flattening (MLSF) experimental set-up and work principle. (a) MLSF experimental set-up; (b) work principle of MLSF

Fig. 2. Electron copper foil and K9 glass used in our experiment. (a) Copper foil; (b) K9 glass

Fig. 3. Laser spot parameters and diagram of scanning path. (a) Laser spot parameters and energy distribution; (b) overlapping ratio and scanning path of laser spot

Fig. 4. Surface roughness of copper foil before and after MLSF. (a) Three-dimensional morphology and microprotrusion height distribution of copper foil before MLSF; (b) three-dimension morphology and microprotrusion height distribution of copper foil after MLSF for one time (laser pulse energy of 100 μJ); (c) effect of pulse energy on MLSF effect under the fixed overlapping ratio

Fig. 5. Effects of MLSF times on surface roughness of copper foil. (a) Three-dimensional morphology and microprotrusion height distribution of K9 glass; (b) three-dimensional morphology and microprotrusion height distribution of copper foil after three times MLSF; (c) effect of MLSF times on surface toughness (No.1: annealed copper foil; No.2: copper foil flattened by MLSF for one time; No.3: copper foil flattened by MLSF for two times; No.4: copper foil flattened by MLSF for three times; No.5: K9 glass)

Fig. 6. Damage of K9 glass surface after different MLSF times. (a) One time; (b) two times; (c) three times

Fig. 7. Amplification principle of shock wave and propagation principle of microscale shock wave. (a) Propagation and amplification principles of shock wave in multilayered media; (b) MLSF principle of copper foil; (c) one dimensional plane wave propagation principle; (d) two dimensional ellipsoid wave propagation principle

Fig. 8. Microstructures in annealed and flattened copper foils. (a) Transmission electron microscopy (TEM) image of annealing twins and dislocations; (b) selected area electron diffraction (SAED) pattern of annealing twin; (c) inverse fast Fourier transform (IFFT) image of micro-region of annealed copper foil; (d) TEM image of dislocation cells near grain boundary of flattened copper foil; (e) TEM image and SAED pattern of dislocation cells and dislocation tangles in flattened copper foil; (f) IFFT image of micro-region of flattened copper foil (DT: dislocation tangle; TB: twin boundary; DC: dislocation cell; GB: grain boundary)

Fig. 9. Surface deformation mechanism of MLSF. (a) Molecular dynamics simulation of laser shock polishing^[17]; (b) surface contour curve of original copper foil; (c) surface profile of electronic copper foil after 100 μJ single laser shock (its height is amplified for comparison); (d) schematic of surface deformation mechanism of MLSF