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.