Ultrafast laser desorption from transparent insulators

Positive ion emission upon irradiation with trains of ultra short laser pul ses from an amplified titanium:sapphire laser (pulse duration 120 fs, photo n energy 1.55 eV) shows significant differences between Al2O3, and NaCl tar gets. For both types of crystals, an incubation phase of several hundred la ser pulses is necessary to prepare the target for the emission of detectabl e amounts of positive ions. Thereafter, in the case of Al2O3, ion bursts ar e observed depending stochastically on the number of additional laser pulse s, while such an explosive ablation is not observed for NaCl. Evidence for different incubation and ablation mechanisms for both materials is presente d, pointing to an important role of recondensation during multi-shot laser ablation. (C) 2000 Elsevier Science B.V. All rights reserved.