Abstract
A new approach to metamaterials is presented that involves laser-based patterning of novel chiral polymer media, wherein chirality is realized at two distinct length scales, intrinsically at the molecular level and geometrically at a length scale on the order of the wavelength of the incident field. In this approach, femtosecond-pulsed laser-induced two-photon lithography (TPL) is used to pattern a photoresist-chiral polymer mixture into planar chiral shapes. Enhanced bulk chirality can be realized by tuning the wavelength-dependent chiral response at both the molecular and geometric level to ensure an overlap of their respective spectra. The approach is demonstrated via the fabrication of a metamaterial consisting of a two-dimensional array of chiral polymer-based L-structures. The fabrication process is described and modeling is performed to demonstrate the distinction between molecular and planar geometric-based chirality and the effects of the enhanced multiscale chirality on the optical response of such media. This new approach to metamaterials holds promise for the development of tunable, polymer-based optical metamaterials with low loss.
Highlights
Metamaterials are artificial electromagnetic materials with constituent elements that are subwavelength in size relative to the incident field and engineered to produce bulk electromagnetic properties not readily found in nature
The majority of research on metamaterials has focused on developing negative index materials (NIMs) as first proposed by Veselago [3]
Many of the early NIMs operating at GHz and THz frequencies made use of an electromagnetic resonance involving subwavelength metallic structures such as split-ring resonators (SRR) [19] and pairs of cut wires (PCW) [20, 21]
Summary
Metamaterials are artificial electromagnetic materials with constituent elements that are subwavelength in size relative to the incident field and engineered to produce bulk electromagnetic properties not readily found in nature. The majority of such materials for THz applications have been fabricated using “top-down” techniques such as electron-beam lithography (EBL) or focusedion beam (FIB) milling [23] While these methods provide an Advances in OptoElectronics adequate nanometer resolution for tailoring subwavelength constituent elements, they tend to be limited to the fabrication of 2D planar materials on rigid substrates at low throughput and with high cost. In the chiral approach to NIMs, a negative index can potentially be achieved with a wider bandwidth and lower loss as there is no need to introduce lossy resonant metallic constituents. Our strategy is to use a laser to fabricate materials with enhanced multiscale chirality (sufficiently large κ) in order to obtain polymer-based NIMs without resorting to top-down fabrication or resonant metallic structures as is common in conventional approaches to metamaterials. We present modeling results that demonstrate the effects of multiscale chirality on the optical response (optical rotation) of such media
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