Abstract: Fabrication of nanostructures on a surface of p-aminoazobenzene polymer film illuminated by 400 nm and 800 nm femtosecond laser was studied. Ripples with periods of 210 nm and 500 nm were produced by linearly polarized 400 nm and 800 nm femtosecond laser pulses, respectively. The periods of the ripples increase with increasing the intensity of incident laser pulses. The interference of this diffracted optical wave with the incident beam gives rise to optical interference ripples. Gradient of surface tension is induced by the surface temperature gradient caused by the interfered light. The gradient of surface tension gives rise to the periodical ripple structures. Thick polymer film was made and illuminated by 400 nm femtosecond laser，and periodic nanostructures were also been observed.

Key words: optical material, femtosecond laser, p-aminoazobenzene, micopolarization elements, periodic nanostructures