Explosive ion emission from sapphire upon femtosecond excitation

Summary form only given. Femtosecond laser ablation of positive ions from transparent, polished slides of single crystalline Al/sub 2/O/sub 3/ is studied by time-of-flight mass spectrometry. The incident fluence from an amplified Ti:Sapphire laser could be varied between 0.5 J/cm/sup 2/ and 2.7 J/cm/sup 2/, the maximum being well below the single-shot damage threshold for Al/sub 2/O/sub 3/ at 3.0 J/cm/sup 2/. We investigated the emission of positive ions, negative ions, and electrons, usually averaging the signals over several hundred pulses. All experiments were conducted in the previously described ´strong etch´ regime, i.e. after a preceding incubation the samples show a strong response to the incident radiation. In this regime, the ion emission is characterized by a stable average rate, consisting of stochastically alternating pulses with high and with low yield. Thus, sampling over 500 pulses for each data point leads to stable, reliable, and reproducible results.