Use of a single-mode fiber coupler for second-harmonic-generation microscopy.

We present a compact second-harmonic-generation (SHG) microscope based on a three-port single-mode fiber coupler. The fiber coupler is used to deliver a near-infrared ultrashort-pulsed laser beam as well as to collect the SHG signal in the visible wavelength range. The SHG microscope exhibits an axial resolution of 1.8 microm, which shows a slight enhancement of the optical sectioning effect compared with that for two-photon excitation at the same excitation wavelength. It is also demonstrated that SHG and two-photon fluorescence images under parallel and perpendicular laser excitation polarization can be simultaneously obtained.