Ru. Maheswari et al., POWER SPECTRAL-ANALYSIS FOR EVALUATING OPTICAL NEAR-FIELD IMAGES OF 20 NN GOLD PARTICLES, Optics communications, 131(1-3), 1996, pp. 133-142
We have demonstrated that the power spectral analysis could be employe
d as a potential tool for evaluation of near-field optical images of c
olloidal gold particles of size 20 nm fixed on a glass substrate. It h
as been found that the power spectral density of the near-field image
resembles the Airy pattern due to a circular dot with the first minimu
m occurring at the spatial frequency 5.6 x 10(7) m(-1). This correspon
ds to an estimated particle diameter of 22 nm. From a comparison with
the theoretical power spectral density of randomly distributed circula
r dots, the transfer function of the near-field optical microscope has
been estimated. It has been found that the resolution estimated using
similar to 3 dB cutoff value obtained from the transfer function was
0.8 nm which is much higher than that determined by aperture size. The
high resolving ability of the present microscopic system is believed
to be due to the confinement of very high spatial frequency evanescent
fields around the edges of the metal-glass fiber boundary at the apex
of the apertured probe.