Femtosecond off-axis digital holography for monitoring dynamic surface deformation

Abstract

We present a femtosecond off-axis digital holography for investigating the dynamic reversible surface change of a metal film induced by femtosecond laser pulses with fluences near the ablation threshold. A reflection Michelson interferometer (RMI) and a transmission Mach–Zehnder interferometer (TMZI) are integrated in the same setup for recording digital holograms. The RMI is used to measure the laser-induced surface deformation of the metal film, while the TMZI is used to analyze the refraction index change of the metal film induced by the femtosecond laser pulses. Experimental results show that both surface modification and refraction index change of chromium metal film can be observed when femtosecond laser pulses are below and above the ablation threshold. Based on the experimental results, the physical processes of the metal induced by femtosecond laser pulses are given qualitatively.