We demonstrate that the optical response of a single Au bowtie nano-antenna (BNA) can be favorably modified
to increase the local intensity by a factor of 103 in the feed gap region when a periodic array of BNAs are used.
We use the periodicity of the arrays as an additional degree of freedom in manipulating the optical response and
investigate the behavior of the resultant nonlinear emission, which include second harmonic generation (SHG),
two-photon photoluminescence (TPPL), and an additional photoluminescence that cannot be attributed to a
single multiphoton process. We discuss the effects of the array with respect to the nonlinear emission and also find
that the considerable field enhancement of our antenna system leads to a broadband continuum whose spectral
response is highly controllable. Resonantly excited arrays of BNAs were seen to exhibit a remarkably uniform
emission over 250 nm of the visible spectrum. In addition, our analysis suggests that high field enhancements,
as well as resonance matching, may not be the only preconditions for enhanced nonlinear emission. To our
knowledge, this is the first report of implementing optical antennas in an array to favorably augment its optical
response.
In this paper we report investigations on mapping of surface plasmon polaritons (SPPs) on nanostructured thin film disks
using electron-beam excitation. Square and circular disks with sub-micron characteristic dimensions were patterned
using electron-beam lithography. Two-dimensional confinement of SPPs resulted into standing wave patterns that were
imaged using cathodoluminescence spectroscopy. Several modes of the disks were identified and were found to be
dependent on disk geometry as well as position of the electron beam. Detailed analysis of specific modes is provided
using panchromatic imaging of the disks. SPP wavelengths as small as 100 nm are predicted from the dispersion curves
of 15 nm thick Ag films. Extremely small mode volumes on disks as small as 65 nm are mapped. Our investigations
enhance understanding of light-matter interaction at nanoscale with potential applications in various areas including
photonics, optoelectronics, chemical and biological sensing, and next generation optical communication.
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