Fully two-dimensional metamaterials, also known as metasurfaces comprised of planar-chiral plasmonic metamolecules that are just nanometers thick, have been shown to exhibit chiral dichroism in transmission. The origin of the resulting circular dichroism is rather subtle. Theoretical calculations indicate that this surprising effect relies on finite non-radiative (Ohmic) losses of the metasurface. In the absence of such losses on the nanoscale, the chiral dichroism in transmission (CDT) defined as the difference between the transmission coefficients of the RCP and LCP waves, must identically vanish.
This surprising theoretical prediction has never been experimentally verified because of the challenge of measuring non-radiative loss on the nanoscale. We use a combination of nanoscale characterization techniques to demonstrate that the RCP and LCP states of the incident light produce drastically different distributions of optical energy and Ohmic heat dissipation in the two-dimensional chiral nanoantennas, thereby producing a strong chiral dichroism in absorption (CDA). A planar-chiral metasurface, along with its chiral enantiomer, was designed to maximize the CDA in mid-IR range. The CDA gives rise to the CDT observed experimentally in the far-field measurements. We then use scattering-type near-field scanning optical microscopy to map the optical energy distribution on the nanoantennas and their enantiomers in response to the RCP and LCP light. Photo-expansion microscopy, also known as AFM-IR, was then utilized to experimentally demonstrate drastically different Ohmic heating of the nanoantennas under RCP and LCP light illumination. In collaboration with: A.B.Khanikaev, N.Arju, Z.Fan, D.Purtseladze, F.Lu, J.Lee, P.Sarriugarte, M.Schnell, R.Hillenbrand, M.A.Belkin
Gennady B. Shvets, "Experimental demonstration of the microscopic origin of circular dichroism
(Conference Presentation)," Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 99180K (Presented at SPIE Nanoscience + Engineering: August 29, 2016; Published: 9 November 2016); https://doi.org/10.1117/12.2239083.5159519575001.
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