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Far-and Near-Field Optical Second-Harmonic Microscopy of Domain Structures

Abstract:

Local probing of second-order susceptibilities with a scanning near-field optical microscope and a conventional far-field microscope arrangement is demonstrated for domain structures in a periodically poled LiNbO 3 crystal and a multilayer Langmuir-Blodgett film of 2-docosylamino-5-nitropyridine (DCANP). In the first configuration, an uncoated fiber tip is used as a light source, and the transmitted radiation at the fundamental and second harmonic (FH and SH) wavelengths is detected while simultaneously recording surface topography. The experimental setup used consists of a stand-alone illumination scanning near-field optical microscope combined with a shear force based feedback system. The linearly polarized light beam from a mode-locked Ti-Sapphire laser (λ ω~ 800 nm, P ω av≈ 200 mW, repetition rate f≈ 80 MHz, pulse duration τ~ 200 fs) is coupled into a single-mode fiber terminated with a sharp …