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Spectral Characteristics of Autofluorescence and Second Harmonic Generation from ex Vivo Human Skin Induced by Femtosecond Laser and Visible Lasers

Jianxin Chen, Shuangmu Zhuo, Tianshu Luo, Xingshan Jiang, Jingjun Zhao*

Key Laboratory of Optoelectronic Science and Technology for Medicine (Fujian Normal University), Ministry of Education, and *Department of Skin, Affiliated Xiehe Hospital, Fujian Medical University, Fuzhou, China

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Summary: The spectral properties of one-photon, two-photon excited autofluorescence and second harmonic generation (SHG) from ex vivo human skin induced by a femtosecond (fs) laser and three visible lasers in backscattering geometry are systematically investigated. Our experimental results indicate that peak position of autofluorescence spectra from the dermis and epidermis shift toward long wavelengths, and the fluorescent intensity decreases when the excitation wavelength increases due to an effect of the excitation wavelength on autofluorescence signals. However, the intensity of the SHG signal in collagen has the maximal value of 800 nm excitation wavelength. This may be the result that the energy of the SHG signal is in resonance with an electronic absorption band. The two-photon excited autofluorescence and SHG intensity all obey a quadratical dependence on the excitation power. Compared with the two-photon excited fluorescence and SHG, the one-photon excited fluorescence in the dermis and epidermis exhibits different spectral characteristics. The investigation of the spectral characteristics of autofluorescence and SHG from ex vivo human skin can provide new insights into morphologic structures and biochemical components of tissues, which are vital for improving the application of laser-induced autofluorescence and SHG spectroscopy technique for noninvasive in vivo tissue diagnostics.

Key words: autofluorescence spectrum, second harmonic generation, ex vivo human skin

PACS: 87.15.-v, 87.15.Mi, 87.90.+y

This project was supported by the National Natural Science Foundation of China (No. 60508017), Program for New Century Excellent Talents in Fujian Province University, Natural Science Foundation of Fujian Province of China (No. A0510015), Innovation Foundation for Young Technological Talents of Fujian Province (NO.2003J027), and Scientific Program of the Educational Hall of Fujian Province (NO.JA05215).