Fig. 3.

(a) Background fluorescence spectra generated from the fiber in fiber-optic spectroscopic setup as a function of excitation wavelength; (b) closer view of the specrtal range containing a SHG signal; (c) background fluorescence signal at 850 nm excitation wavelength (green) and a typical bronchus emission spectrum without background substraction (black) and with background substraction (red). 770 nm excited fiber fluorescence signal prohibites the use of this wavelength. 850 nm excited SHG signal fiber emission is negligeable compared to a typical tissular emission spectrum.