Higher-order multiphoton imaging by femtosecond near-infrared laser microscope system

Near-infrared (NIR) femtosecond laser microscope with Cr:Forsterite laser at ca. 1.26 μm output wavelength was constructed and applied to two-, three- and four-photon imaging of gold nanoparticle and some organic micro crystals. The ultrafast pulse duration of 35 fs after passing through the objectives easily induced higher-order multiphoton absorption. The size of the laser focal spot and the resolution along the optical axis were discussed by comparing the present higher-order multiphoton imaging and two-photon induced processes.