Reconstruction of a surface profile using near field data

This paper reports on the possibility of imaging with a subwavelength resolution. Two basic systems are being used. The scanning near field optical microscope (SNOM) uses a coated fiber with an aperture of 50 nm in the visible range. It illuminates a very small portion of the object and produces an image by detecting the scattered light when the location of the tip is scanned over the object. The second set-up uses an object illuminated by a totally reflected wave. An optical fiber with a radius of curvature of 50 nm at its extremity is scanned over the object and detects the field scattered by the object provided that the tip is within the decay length of the evanescent waves. This set-up is known as photon scanning tunneling microscope (PSTM). This apparatus is generally operated in the so called constant intensity mode. In this case, it is assumed that a constant signal indicates a constant distance to the surface. Hence, the topography can be deduced in principle from the displacement of the tip. In fact, the results have shown a much more complex behavior of the signal and the relationship between the signal and the topography seems to be more complicated.