Creation of micro/nano surface structures on silver using collinear double femtosecond laser pulses with different pulse separation

Self-organized mound-like micro/nanoscale structures are reported for the first time on silver using a dual-pulse femtosecond laser surface processing technique. The dual-pulse laser processing technique reported in this paper uses femtosecond laser pulse pairs with a controlled temporal delay between the leading and trailing pulses. Using dual pulses at higher fluence values, mound-like micro/nanostructures have been created on silver samples for the first time. Formation of the self-organized microstructures is shown to be dependent on the time delay between the leading and trailing pulses. Mound-like microstructures do not develop on silver for overlapped pulses or using single-pulse femtosecond laser surface processing for the parameter space studied. Subsurface microstructure characterization of a single mound-like surface structure is analyzed by cross-sectional analysis using focused ion beam milling followed by scanning electron microscopy and energy dispersive X-ray spectroscopy.