Three-dimensional wavefront imaging by near-field scanning optical microscopy

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Abstract
We have designed a near‐field scanning optical microscope head compatible with an existing commercial scanning probe system. Near‐field images of coherent scattering from a 500 nm fused silica grating are collected in transmission mode as a function of tip‐sample separation, wavelength, and incident polarization. The images are compared with numerical simulations of scattering using both scalar wave and vector dipole approximations. The simulations suggest that the procedure can be inverted, allowing one to measure the dielectric constant ε(x,y,z) of an embedded three‐dimensional object using information obtained in the near field.