Laser-blood cells interaction was studied by Ar+ laser-induced animal (mouse) blood fluorescence spectra in vitro. The fluorescence spectra of the blood under various irradiated powers of Ar+ laser excitation are shown that there are very rich and sharp spectral peaks from 600 nm to 860 nm. These peaks are located at 616 nm, 666 nm, 708 nm, 739 nm, 752 nm, 766 nm, 800 nm, 812 nm and 844 nm. This may be due to the fact that there are various fluorophores in the blood and the ground electronic state of the fluorophores containing a large number of vibrational levels. In addition, 666 nm peak among them is the most prominent and is a larger change in the intensity under different power of Ar+ lasers excitation. It foretell that laser near a wavelength of 666 nm may be more effective to low lever laser therapy (LLLT). Furthermore, these experiments indicate that when the laser irradiated power density reaches to 30 mW/cm2 the blood cells are still not destroyed. The results may be significative for the choice of irrediation-wavelength in LLLT.
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