P. Zhang et al., MODE LOCALIZATION IN SELF-AFFINE FRACTAL INTERFACES OBSERVED BY NEAR-FIELD MICROSCOPY, Physical review. B, Condensed matter, 57(24), 1998, pp. 15513-15518
Near-field optical microscopy with simultaneous topographic imaging sh
ows that for a given excitation wavelength the electromagnetic optical
fields excited in a self-affine film are highly localized at ''hot sp
ots'' whose dimensions are often smaller than the wavelength. The patt
ern of hot spots varies greatly with excitation wavelength and does no
t correlate simply with the film topography. This observation is consi
stent with a recent theory of the optical response of self-affine frac
tal objects and also indicates that the locus of optical effects such
as surface-enhanced Raman does not reside in special surface sites suc
h as interstices. Additionally, we show that the conclusions of the th
eory, which was based on a quasilocal approximation, are qualitatively
valid for self-affine films considerably larger than the exciting opt
ical wavelength.