Various structural changes in SiO2 introduced by one-photon excitation with undulator and two-photon excitation with excimer laser

Abstract

Excitation at higher energies beyond the ultraviolet (UV) edge (∼9eV) in amorphous SiO2 (a-SiO2) can be achieved by two-photon process with ArF excimer laser as well as by one-photon process with undulator radiation. Photo-induced phenomena with two kinds of light sources are reported. Frequency decrease of the SiO stretching vibration in infrared absorption spectrum was observed in the a-SiO2 by one-photon process with 14.1eV rays and higher. Frequency decrease can be explained with transition from regular six membered ring (6 Si and 6 O in a loop) to three and four membered rings (3 (4) Si and 3 (4) O in a loop) in a-SiO2 network. In case of two-photon process with ArF excimer laser, ablation was observed. Threshold fluence ∼1Jcm−2 is apparently necessary to commence ablation by a single pulse. Ablation introduced with a single pulse above the threshold fluence did not influence stoichiometry of SiO2. In contrast, for lower fluence below the threshold, the ablation commenced after several pulses accompanied with oxygen loss and ablated thickness increased via a cumulative process. Photo-ablation below the threshold fluence 1Jcm−2 obeyed two-photon excitation process, in contrast, ablation obeyed multi-photon process above the threshold fluence.