Direct observation of enhanced residual thermal energy coupling to solids in femtosecond laser ablation

We perform direct measurement of the thermal energy remaining in the bulk of Cu, Mg, Au, and Si samples following multi-pulse femtosecond laser ablation. In contrast to the previous belief that the thermal energy remaining in the ablated sample is negligible using femtosecond pulses, we show a significant amount of residual thermal energy deposited in various materials. In fact, with a sufficiently large number of pulses at high fluence, virtually all the incident laser energy can be retained in the sample. Several possible mechanisms are investigated for their role in residual heating, including laser-induced surface modification, exothermic chemical processes, and pressure effects. (C) 2005 American Institute of Physics.