A technique is suggested to measure a threshold of two-photon initiated photopolymerisation involving Z-scan of a thin film of sensitive material along the focusing axis of the laser beam. The condition of reaching the threshold when gradually increasing the light intensity by moving the film towards the focal spot of the beam is defined as that with minimal intensity at which polymerization occurs. The occurrence of the polymerization is detected by interferometric effect inside the transmitted beam itself, which is due to interference of the wave going through the polymerization area and the wave going around it. The technique is demonstrated for measurements employing Nd:YAG laser in nanosecond regime with fundamental frequency 1064 nm and its harmonic of 532 nm, as well as with pumped by its third harmonic optical parametric oscillator. Threshold data are presented for particular systems, indicating threshold of 5 GW/cm² for a system based on Rose Bengal exposed by 1064 nm nanosecond-pulsed radiation and 0.05 GW/cm² for Darocur initiators exposed to 532 nm.

Date Published: 23 February 2010
PDF: 4 pages
Proc. SPIE 7585, Laser-based Micro- and Nanopackaging and Assembly IV, 75850W (23 February 2010);

Published in SPIE Proceedings Vol. 7585:
Laser-based Micro- and Nanopackaging and Assembly IV
Wilhelm Pfleging; Yongfeng Lu; Kunihiko Washio; Jun Amako; Willem Hoving, Editor(s)