Ablation of Dielectric Materials by Induction of a Phase Explosion using a Mid IR FEL

(WE-Wrk-1-04)

D. R. Ermer, M. R. Papantonakis, M. Baltz-Knorr, R. F. Haglund, Jr.  

Vanderbilt University

We have demonstrated efficient, fracture free ablation of brittle dielectric materials by depositing energy using an IR FEL tuned to a strong vibrational resonance. Under the conditions employed, the ablation is not well described by models of melting and vaporization. Rapid deposition of energy superheats the material to a temperature where explosive homogeneous nucleation of vapor occurs (a phase explosion). By knowing the thermodynamic properties of the material, the optimum laser wavelength, pulse width, and fluence may be calculated. Clean ablation of this type is possible by other means (e.g. laser-induced breakdown) but requires ultrafast lasers and may generate unwanted electronic excitations and decay products. By comparing results obtained with the FEL to a phase explosion model, we believe that similar results may be possible using nano-second lasers operating in the mid-infrared. In the case of SiO2 the same quality of ablation may be obtained with a CO₂ laser operating at the peak of the Si-O stretch (9.2 microns).