We show how Newton's rings manifest themselves in near-field scanning optic
al microscopy and discuss how this effect can be used with topographic imag
ing to measure correlated roughness of thin films. In conventional optics,
transmission through a thin nonabsorbing film depends on film thickness whe
n multiple reflections from the film boundaries are coherent. Measurements
and modeling of the transmission through thin films illuminated by a near-f
ield probe show that these oscillations are present despite the large distr
ibution of transverse wave vectors needed to describe light from the probe.
(C) 2001 American Institute of Physics.