Dynamics of laser desorption and ablation of metals at the threshold on the femtosecond time scale

The dynamics of the laser-ablation (-desorption) process of metals (Al, Ag, Fe, and Ni) initiated by 30 fs laser pulses has been investigated by inter ferometric time-resolved pump-probe measurements. It is postulated that a s ufficiently high density of hot electrons is essential for achieving desorp tion of metal ions. In addition, we have observed a new and unexpected beha vior characterized by delayed ablation for a pump-probe beam delay in the r ange of several ps for Al, Ni, and Fe. This second peak is attributed to th e development of a liquid surface layer developing after a few ps. Molecula r dynamics simulations support this assumption.