Fig. 5.
(a) A diagram of the laser beam focusing in a cell. The position z = 0 is set in the middle of the cell nucleus and the third-order susceptibility of the nucleus is equal to the susceptibility of the cytoplasm. (b) Numerical simulations of THG intensities versus beam focusing position z with different thickness of the cell nucleus (L). (c) Transverse histological image of human oral mucosa. The thicknesses of cell nuclei in the superficial cell layer (white arrow) and the deeper epithelial cell layer (yellow arrow) are 3.36 ± 0.94 μm and 9.03 ± 0.71 μm, respectively.