The role of energy and phase relaxation (T1 and T2)in ultrafast laser ablation

The dynamics of ultrafast laser ablation have been studied by pump-probe experiments, monitoring the ablated ions by time-of-flight mass spectroscopy. For both dielectric and metal target materials, despite their substantial physical difference, a rather similar, general dependence of the ion yield on the pump-probe delay has been observed: for short delays, the typical "coherence" peak occurs, then the signal goes down to zero, and after a longer delay, the signal increases again. This behaviour is discussed in a picture of energy and phase relaxation (T-1, T-2) mechanisms.