Abstract
The fluorescence of melanin in human skin tissue reflects the structural changes in the process of skin cancer progression towards malignant melanoma. A selectively excitation of melanin in skin tissue, however, is only possible by stepwise two-photon absorption (TPA) in the NIR spectral range (λ exc ≈ 800 nm). Due to the very short lifetime of the energy level populated by the absorption of the first photon (< 5 ps) an effective TPA process can be only achieved with laser pulses on the femtosecond time scale. To use the two-photon excited fluorescence (TPF) of melanin for early diagnosis of malignant melanoma a small, mobile TPF spectrometer was developed. It consists (i) of a fiber laser the radiation of which was amplified in a short pulse nitrogen laser pumped dye cell, (ii) an articulated arm with special mirrors for nearly lossless direction of the fs laser beam to the skin position of investigation, (iii) a camera objective which include visualization and excitation as well as acquisition of fluorescence and (iv) a monochromator with a multichannel photomultiplier and a PC with special software for spectrometer control and data processing. First investigations of the equipment concerning the early diagnosis of malignant melanoma were carried out.
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