A Photon Scanning Tunneling
Microscope (PSTM) is a device where the object is illuminated by an
evanescent wave generated at the face of a prism or slide and the field
is detected via a fiber probe in the near-zone of the sample (as in
NSOM). PSTM measurements are inherently holographic since the
sample is illuminated by an evanescent field and that same field serves
as reference. The measurements are thus the near-field equivalent
of a Gabor hologram. This hologram may be measured a large
fraction of a wavelength from the sample, where the near-field is
normally out of focus, as may be seen in reference. It is
demonstrated here that the data thus obtained, though not amenable to
direct interpretation, provide enough information to determine
quantitatively the two-dimensional structure of a thin sample,
thus achieving a computational lens for the near-field.
FIG. 1. The PSTM instrument. A HeNe
laser (L) emits a collimated beam that is divided at the beam splitter (BS)
and propagated on one of two possible paths, (A) or (B), the other path
being blocked. The beam is routed by mirrors (M) to the prism at an angle
such that the beam in the prism (P) is totally internally reflected.
The evanescent field outside the prism interacts with the sample (S)
and the total field is detected by the tapered fiber probe (F) which
is scanned in a plane at fixed height.
FIG. 2. The data are displayed in panels (a) and (b). The colorbar indicates
normalized photocount with the constant background subtracted. The result
of the reconstruction algorithm is displayed in panel (c). An AFM image
is displayed in panel (d) for comparison. The field of view in each image
is 3.4um X 5um.
This project is being funded by an Airforce MURI grant.
- P S Carney, R A Frazin, S I Bozhevolnyi, V S Volkov, A
Boltasseva, and J C Schotland, "A computational lens for the
near-field,"Phys. Rev. Lett.92 163903 (2004). PDF
See theFunding page for more details