This conference presentation was prepared for the Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XX conference at SPIE Optics + Photonics 2022.
Optical meta-devices using metasurfaces have shown preeminent capabilities to control the optical nonlinearity and enhancing the nonlinear efficiency by arrangements of meta-atoms. With the great advantages of relaxed phase-matching requirements and CMOS compatibility for mass production, nonlinear metasurfaces can flexibly manipulate the phase, amplitude and polarization of the nonlinear waves at subwavelength scale. Various nonlinear frequency conversion processes, such as second harmonic generation (SHG), third harmonic generation (THG), have been widely realized to short wavelength such as vacuum ultraviolet (VUV) light and applied in optical communication, imaging, photochemistry and biosensing. The design, fabrication and application of the novel nonlinear optical meta-devices are reported in this talk.
Substantial effort has been invested in generating narrow bandwidth visible colors from metasurfaces using a wide variety of geometries and materials. In this work we continue these explorations and demonstrate how a combination of a plasmonic Fano resonance and a Bragg reflector can contribute to the generation of narrowband visible colors. We demonstrate active tuning of these colors by stretching the array in the x- and y- directions and the reflector in z- to shift the colorimetric response of both elements. The combination of these two types of photonic structures allows for substantially increased flexibility in design and color-space tuning. Additionally, by fabricating these structures at scale, this methodology could prove useful towards the manufacture of agile metasurface color pixels
Large-area plasmonic metasurfaces have attracted interest as potential tools for a wide range of applications, from colorchanging glass to improved efficiency of solar cells. These potential applications necessitate the capability to fabricate such surfaces at scale. One potential approach to resolve this issue is to use nanoimprint lithography to mold a metasurface structure and then use chemically synthesized nanoparticles as the metallic elements. By combining aluminum nanoparticles with electrophoretic deposition, a low-cost method of scalable fabrication could be achieved.
KEYWORDS: Near field, Plasmonics, Atomic force microscopy, Near field optics, Gold, Nanostructures, Lithium, Metamaterials, Current controlled current source
We demonstrate the ability to map photo-induced gradient forces in materials, using a setup akin to atomic force microscopy. This technique allows for the simultaneous characterization of topographical features and optical near-fields in materials, with a high spatio-temporal resolution. We show that the near-field gradient forces can be translated onto electric fields, enabling the mapping of plasmonic hot-spots in gold nanostructures, and the resolution of sub-10 nm features in photocatalytic materials. We further show that the dispersion-sensitive nature of near-field gradient forces can be used to image and distinguish atomically thin layers of 2-D materials, with high contrast.
KEYWORDS: Image enhancement, Gold, Near field optics, Plasmonics, Microscopy, Near field scanning optical microscopy, Near field, Imaging systems, Plasmons
Nanophotonic systems such as plasmonic and 2-D materials and metamaterials serve as excellent platforms to study and control several optical and chemical phenomena such as spontaneous emission, absorption, Raman scattering and photocatalysis. Techniques such as atomic force microscopy and scanning electron microscopy enable the imaging of nanoscale features, while other techniques such as scanning tunneling microscopy and scanning near-field optical microscopy, enable the near-field optical characterization of nanoscale materials. However, most of these techniques do not allow for simultaneous imaging of topographical features and spectroscopic characterization with high spectral selectivity and temporal resolution. Here, we make use a new imaging technique called photo-induced force microscopy [1,2], which enables imaging and optical characterization of nanoscale materials with very high spatial and temporal resolution. In this technique, a nanoscale tip is brought in the vicinity of the sample, which is optically excited. The photo-induced gradient forces between the tip and the sample can be detected with nanometer-scale spatial resolution, along with topographical information, akin to an atomic force microscope. The photo-induced gradient forces, which are very sensitive to polarization and the distance of the tip from the sample, can be read out and converted to electric fields [2]. As a proof-of-concept demonstration, we image the transverse and longitudinal resonances in gold nanorods and compare their field enhancements to gap plasmons of gold dimers.
[1] J. Jahng et al. Gradient and scattering forces in photo-induced force microscopy. Phys. Rev. B 90, 155417 (2014).
[2] F. Huang et. al., Imaging nanoscale electromagnetic near-field distributions using optical forces, Sci. Rep. 5, 10610 (2015).
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