Abstract
Spectroscopic measurements including absorption and fluorescence were performed using pheophorbide a dissolved in PBS, which was excited by the fundamental output of a Q-switched Nd: YAG laser and its second harmonic beam. The visible fluorescence thus observed by Nd: YAG laser irradiation was attributed to the two-photon absorption process, although its intensity was about 10-4 weaker than the case of second harmonic excitation. In vitro experiments using TE-2 cultured esophagus cancer cells uptaken pheophorbide a and Nd: YAG laser output were also carried out. Survival rates of TE-2 cancer cells exhibited exponential decreases with the irradiation time for different dye concentrations, and this two-photon photochemical effect was found more appreciably for higher dye concentration and higher energy density of irradiation laser pulse.
