Multiphoton excitation of selected dye molecules for laser-induced fluorescence diagnosis (LIFD) and optical biopsy of biological tissue and microbiological samples has various advantages: greater tissue penetration, more spatial resolution and less photo-bleaching. New applicators and microscopical set-ups for the delivery of the fs-pulsed laser radiation as required for multiphoton LIFD and optical biopsy need to be developed. Beam delivery solutions and workplaces for microbiological and tissue diagnosis are presented.
Multiphoton excitation of photosensitizers for laser induced fluorescence diagnosis (LIFD) and photodynamic therapy (PDT) of tumors has the advantage of greater tissue penetration due to the longer wavelength of irradiation. However, multiphoton LIFD and PDT are presently not clinically applicable as there are no applicators available for the delivery of the pulsed laser radiation to the operating room. As an approach, in this contribution the beam delivery through photonic crystal fibers has been investigated. Pulses of a Ti:sapphire laser of 100 fs pulse duration and an average power of 150 mW have been transported through such a fiber of 25 m length and the resulting pulses show the absence of nonlinear contributions but still a broadening of the pulse to 2 ps due to the dispersion of the fiber. It is planned to compensate this broadening by a grating in front of the fiber. Alternatively, the transport of laser radiation of 150 fs and 100 mW through a mirror-joint-arm used for conventional CO<sub>2</sub> lasers has been tested showing no broadening of the laser pulses. Two-photon photodynamic activity of mTHPC-CMPEG4 shall serve as a test of the laser light transport system.