Cationic two-photon induced polymerization with high dynamic range

Cationic-induced two-photon photo-polymerization is demonstrated at 710 nm, using an isopropylthioxanthone / diarylidonium salt initiating system for the cationic polymerization of an epoxide. In-situ monitoring of the polyme r conversion using interferometry allows for determination of the polymeriz ation threshold J(2th), polymerization rate R and its dependence of initiat or's concentration z. Best J(2th) achieved is 1 GW/cm(2), with a dynamic ra nge of > 100, i.e. the material can be fully polymerized at intensities > 1 00 times the threshold level without damage. The R is found to be proportio nal to the m=1.7 power of the intensity, or R = [C (J-J(2th))](m) = [C (J-J (2th))](1.7), which implies a significantly stronger localization of the ph otochemical response than that of free radical photoinitiators. Both R and J(2th) significantly improve when the concentration z of the initiator (oni um salt) increases, reduction of J(2th) exhibiting z(-m) trend. (C) 2001 Op tical Society of America.