Surface Plasmon Resonance Enhanced Scanning Near-Field Pockels Microscope Observation of Polar Structure

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We have developed a scanning near-field optical microscope that can image Pockels effects in ultrathin films such as a monomolecular layers. Pockels effect, sometimes called "linear electrooptic effect" is one of the second-order nonlinear optical processes that occur in a system without any inversion center under electric dipole approximation. Hence a polar structure can be probed with this technique. In addition, this microscope allows us to observe polar structure even in untrathin films because the surface plasmon resonance effect offers high sensitivity for the chance in the refractive index in a media. This promises possible observation of a small change in the refractive index i(<10^<-6>) in ultrathin films.The features of this microscope are :(1)an optical microscope that can prove the polar structure in a untrathin films.(2)the observation can be preformed without any high power lasers(3)we can make spectroscopic measurement easily.(4)we can prove nanometer sized region using a sharp tip.We have observed pattered dye-monomolecular layers adsorbed on a 45nm-thick thin gild film. The pattered size was 40x40μm. The Pockels images taken in the surface plasmon resonance condition were compared with the images obtained by second-harmonic generation microscopy that can also probe a polar structure, and confirmed a high correspondence between them. Although the present resolution is limited within about 10μm, it is likely that use of a sharp tip and a piezo stage with high resolution will provide much higher resolution.