K. Awazu, Various structural changes in SiO2 introduced by one-photon excitation with undulator and two-photon excitation with excimer laser, APPL SURF S, 168(1-4), 2000, pp. 92-95
Excitation at higher energies beyond the ultraviolet (UV) edge (similar to9
eV) 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. Fre
quency decrease of the Si-O stretching vibration in infrared absorption spe
ctrum was observed in the a-SiO2 by one-photon process with 14.1 eV rays an
d 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 p
rocess with ArF excimer laser, ablation was observed. Threshold fluence sim
ilar to1 J cm(-2) is apparently necessary to commence ablation by a single
pulse. Ablation introduced with a single pulse above thr threshold fluence
did not influence stoichiometry of SiO2. In contrast, for lower fluence bel
ow the threshold. the ablation commenced after several pulses accompanied w
ith oxygen loss and ablated thickness increased via a cumulative process. P
hoto-ablation below the threshold fluence 1 J cm(-2) obeyed two-photon exci
tation process, in contrast, ablation obeyed multi-photon process above the
threshold fluence. (C) 2000 Elsevier Science B.V. All rights reserved.