Evolution of aluminum surface irradiated by femtosecond laser pulses with different pulse overlaps

We report the modification of aluminum surfaces by femtosecond laser pulses with different pulse overlaps in ambient air. Several kinds of structural colors can be generated on the aluminum surfaces by varying the pulse overlap from −27% to 99%. The SEM images reveal that the structural colors of the modified area depend on the surface morphology. Furthermore, X-ray photoelectron spectroscopy and X-ray diffraction spectra show that the content of Al2O3 increases while that of Al(OH)3 decreases with the increase of the pulse overlap. Only Al2O3 is formed on the aluminum surfaces when the pulse overlap is larger than 93%.