The two-photon spectrum of iron and silicon detected by resonant laser ablation

We report ionization spectra of Si and Fe atoms ablated at low fluence from bulk Si and Re targets, respectively. Two-photon transition intensities are calculated using second-order perturbation theory. We obtain moderate agreement between experimental and calculated intensities, assuming a temperature of 1100±200 K for Fe ablation from Re. Si and Fe are detected in excited electronic states up to 1.9 and 1.5 eV, respectively. Ablation of electronically excited Si is enhanced with exposure to oxygen or water. This effect is compared with a similar effect observed in ion induced sputtering of Si and other materials.