This study describes an experimental investigation of the photosensitizer mTHPC (meso-tetra (hydroxyphenyl) chlorin), which is used in photodynamic therapy (PDT) and is available commercially under the trade name Foscan. The studies concentrate on two main topics related to the dynamic behaviour of this photosensitizer under laser exposure: (i) Cellular level fluorescence photobleaching using a micro-spectroscopic laser excitation technique. (ii) Two photon excited fluorescence and PDT using femtosecond duration pulses from a Titanium Sapphire laser emitting at 800 nm.