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
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.
Recent theoretical and experimental studies have shown that imaging with resolution well beyond the diffraction
limit can be obtained with so-called superlenses. Images formed by such superlenses are, however, in the near
field only, or a fraction of wavelength away from the lens. In this paper, we propose a far-field superlens (FSL)
device which is composed of a planar superlens with periodical corrugation. We show in theory that when an
object is placed in close proximity of such a FSL, a unique image can be formed in far-field. As an example, we
demonstrate numerically that images of 40 nm lines with a 30 nm gap can be obtained from far-field data with
properly designed FSL working at 376nm wavelength.
We present S and P polarized measurements of artificial bianisotropic magnetic metamaterials with resonant behavior at infrared frequencies. These metamaterials consist of an array of micron sized (~40μm) copper rings fabricated upon a quartz substrate. Simulation of the reflectance is obtained through a combination of electromagnetic eigenmode simulation and Jones matrix analysis, and we find excellent agreement with the experimental data. It is shown that although the artificial magnetic materials do indeed exhibit a magnetic response, care must be taken to avoid an undesirable electric dipole resonance, due to lack of reflection symmetry in one orientation. The effects of bianisotropy on negative index are detailed and shown to be beneficial for certain configurations of the material parameters.
We employed micro-electro-mechanical system (MEMS) techniques to fabricate parallel sub-wavelength thin-wire structures of metals on elastomeric matrices. From the transmission measurement by Fourier Transform Infrared Spectroscopy, we observed the depressed plasma frequencies of these thin-wire structures at terahertz (THz) ranges. Furthermore, the behavior of depressed plasma frequencies is very sensitive to the polarization of the applied field. The reasons that these engineered materials exhibit unprecedented properties not observed in nature can be interpreted by two factors: the diluted electron densities and the enhancement of electron mass. In addition, the plasma frequencies are readily tunable over a broad frequency range by extending the elastomeric matrices to change their periodicity. These novel properties of tunable and polarization-dependant plasma frequencies at THz ranges promise abundant striking applications in THz optics.
Near-field multiphoton optical lithography is demonstrated by using ~120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produce the lithographic features with ~ 70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale multiphoton absorption and polymerization in a commercial photoresist, SU-8. Even without optimization of the resist or laser pulses, the spatial resolution of this technique is as high as λ/10, nearly a factor of two smaller than the previous multiphoton lithography in the far field.
Recent theoretical works have suggested the possibility of constructing a diffraction-free lens by using a negative refractive index medium (NRIM). The key theoretical proposition is that evanescent waves can be greatly enhanced by increasing the thickness of the NRIM. We present here experimental evidence on enhanced transmission of evanescent waves via surface plasmon at a thin silver film operating near surface plasma resonant frequency. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. These experiments also demonstrated the broadening of enhanced transmission spectrum as photon energy approaches plasma resonance εAg = -1 condition. These findings represent the first step toward the understanding and realization of a diffraction-free lens by using NRIM.
Micro-stereolithography (μSL) is capable of fabrication of highly complex three-dimensional (3D) microstructures by selectively photo-induced polymerization from the monomer resin. However, during the evaporative drying of structures from liquid resin, the 3D microstructures often collapse due to the capillary force. In this work, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force. The
detachment length of the test structures and adhesion energy of a typical μSL polymer (HDDA) are obtained experimentally which are important for MEMS structure design. Finally, we successfully developed a sublimation process to release the 3D microstructures without the adhesion.