We encoded surface relief micro-gratings on Au-Cr thin films using two-beam interference of femtosecond laser pulses with the durations from 25 fs to 70 fs. The dependence of the fabrication quality on the pulse duration has been investigated both numerically and experimentally. The results revealed that the shorter pulses were preferable to prepare periodical microstructures with minimal ablation fringe width and satisfied fabrication quality. This work has potential applications on periodic functional microstructures fabrication for ultra-fine processing and modi. cation on various materials, especially for intractable materials. (C) 2009 Elsevier B. V. All rights reserved.