When 12:30 PM - 1:30 PM Dec 08, 2006
Where 1013 HH Dow
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Material Removal by Laser Irradiation from Insulating (Wide Bandgap) Materials


Thomas Dickinson, Washington State University

We are interested in the laser-induced emission mechanisms from materials at fluences well below the threshold for breakdown. Under these conditions, very gentle, single atomic layer manipulation of surfaces can often be achieved. We consider both ns and fs pulse width regimes. In the case of wide bandgap materials which are nominally transparent at the laser wavelengths used, we have shown in the past for ns pulses that the interactions are mediated by defects, including defects associated with impurities and deformation. A much clearer and more complete picture of these mechanisms has evolved by more careful characterization and identifying the consequences of defects produced by laser exposure itself. On model materials such as alkali halides, MgO, and CaF2 with bandgaps ranging from 7 – 11 eV, as well as polymers such as PTFE (Teflon) with an equivalent bandgap > 7 eV. We examine particle emission properties vs. fluence, simultaneous absorption measurements and UV-VIS absorption spectroscopy (both transmission and diffuse reflection), and the subsequent atomic layer material removal (using AFM). With this data we construct a model that shows the necessary role of both two photon and single photon absorption for ns UV laser irradiation. For ultrafast laser irradiation, multiphoton absorption dominates. We study material removal in both single pulse mode (so that only existing defects can play a role) as well as multiple pulse mode, where defect production via electron–hole relaxation processes dominate.

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