Figure 2.

a) A short-pulsed excitation laser may produce SHG and TPEF signals, which can be detected in a multiphoton microscope. b) SHG signals, in this case from collagen fibers, always appear at the double-frequency of the excitation light, while the TPEF signals are broadened and Stokes-shifted to a characteristic peak with a longer wavelength. Figure 1b is reprinted with permission from ref [53], copyright 2002 National Academy of Sciences.