We demonstrate that an antenna can be used to realize a near-field opt
ical probe that combines spatial resolution well below the diffraction
limit with transmission efficiency approaching unity. The probe consi
sts of a planar bow-tie antenna with an open-circuited gap at its apex
. We present proof-of-principle measurements using microwave radiation
and discuss scaling the antenna to the visible optical spectrum. (C)
1997 American Institute of Physics.