Due to its extremely low fluorescence quantum yield, in the conventionally (one-photon) excited autofluorescence of
skin tissue, melanin fluorescence is masked by several other endogenous and possibly also exogenous fluorophores (e.g.
NADH, FAD, Porphyrins). A first step to enhance the melanin contribution had been realized by two-photon fs-pulse
excitation in the red/near IR, based on the fact that melanin can be excited by stepwise two-photon absorption, whereas
all other fluorophores in this spectral region allow only simultaneous two-photon excitation.
Now, the next and decisive step has been realized: Using an extremely sensitive detection system, for the first time twophoton
fluorescence of skin tissue excited with pulses in the ns-range could be measured. The motivation for this step
was based on the fact that the population density of the fluorescent level resulting from a stepwise excitation has a
different dependence of the pulse duration than that from a simultaneous excitation (&Dgr;t2 vs. &Dgr;t). Due to this strong discrimination between the fluorophores, practically pure melanin fluorescence can be obtained. Examples for in-vivo,
ex-vivo as well as paraffin embedded skin tissue will be shown. The content of information with respect to early
diagnosis of skin deseases will be discussed.