Fluence and photobleaching effects of mTHPC

The current study relates to the response of mTHPC to exposure using femtosecond duration laser pulses. Experiments using a Ti: sapphire laser delivering ∼130 fs pulses at a wavelength of ∼ 800 nm show that fluorescence can be excited in this photosensitiser, even though the photon energy is less than the energy of the fluorescing state. The fluorescence amplitude is found to exhibit an irradiance dependence of the form In where n ≈ 2, which is consistent with two-photon excitation. Also the effect of photobleaching was studied using one and two photon excitation.