Stefan Waselikowski1,2,
Christian Fischer2,
Jan Wallauer1,2
and Markus Walther1,2,3
1 Freiburg Materials Research Center, University of Freiburg
Stefan-Meier-Strasse 21, D-79104 Freiburg , Germany
2 Department of Molecular and Optical Physics, University of Freiburg
Stefan-Meier-Strasse 19, D-79104 Freiburg , Germany
E-mail: markus.walther@physik.uni-freiburg.de
New Journal of Physics 15 (2013) 075005
(13pp)
Received 7 March 2013
Published 3 July 2013
Online at http://www.njp.org/
doi:10.1088/1367-2630/15/7/075005
Optimal focusing of surface plasmon polaritons in the
center of a
metal disc illuminated by radially polarized terahertz
pulses is demonstrated.
By matching the cylindrical symmetry of the metal structure
with the
radially polarized terahertz field, surface plasmons are
excited along its
entire circumference. Constructive interference in the disc
center produces a
sharp frequency-dependent focal spot well described by a
zero-order Bessel
function. We map the field distributions on the disc by
terahertz (THz) nearfield
microscopy and compare our results with numerical
simulations. For
comparison, the behavior of the plasmonic lens under
linearly polarized THz
illumination is also characterized. The remarkable focusing
capabilities of such
a plasmonic lens together with its simple structure offer
considerable potential
for THz sensing and
imaging applications
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