7 June 2000 Explosive femtosecond ablation from ionic crystals
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Proceedings Volume 3933, Laser Applications in Microelectronic and Optoelectronic Manufacturing V; (2000) https://doi.org/10.1117/12.387576
Event: Symposium on High-Power Lasers and Applications, 2000, San Jose, CA, United States
Femtosecond laser ablation of positive ions from transparent ionic crystals is studied by time-of-flight mass spectrometry. We find an explosive emission of positive ions. The ion yield dependence eon the laser fluence is highly nonlinear. The material is emitted in characteristic bursts, depending chaotically on the number of laser pulses hitting the sample. The mean kinetic energy of the positive ions is on the order of 100 eV while their temperature is only around 1 eV, very similar to supersonic expansion of a molecular jet. The last observation is independent of the ion species, indicating that all ions were born at the same instant and kicked out of the material simultaneously with identical kinetic energy. Negative ions, on the contrary, appear considerably later and are much slower. Al ablation is preceded by effective electron emission. We suggest that the laser generates a high-density plasma. The resulting electrons may possibly escape, due to the short pulse duration, without being disturbed by the build-up of a space charge zone. Subsequently, positive ions are expelled by Coulomb explosion of the unstable surface .Negative ions may be produced much later form the hot sample or by secondary processes.
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Juergen Reif, Juergen Reif, Matthias Henyk, Matthias Henyk, Dirk Wolfframm, Dirk Wolfframm, } "Explosive femtosecond ablation from ionic crystals", Proc. SPIE 3933, Laser Applications in Microelectronic and Optoelectronic Manufacturing V, (7 June 2000); doi: 10.1117/12.387576; https://doi.org/10.1117/12.387576

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