Topography characterization of a deep grating using near-field imaging

Using near-field optical microscopy at the wavelength of 633nm, we image light intensity distributions at several distances above an ~2-(mu)m-deep and a 1-(mu)m-period glass grating illuminated from below under the condition of total internal reflection. The intensity distributions are numerically modeled, and an inversion procedure based on a least-squares-fit optimization is employed to extract the grating geometry from the optical images.