Terahertz circular dichroism spectroscopy of biomaterials enabled by kirigami polarization modulators

Abstract

Terahertz circular dichroism (TCD) offers multifaceted spectroscopic capabilities for understanding the mesoscale chiral architecture and low-energy vibrations of macromolecules in (bio)materials1,2,3,4,5. However, the lack of dynamic polarization modulators comparable to polarization optics for other parts of the electromagnetic spectrum is impeding the proliferation of TCD spectroscopy6,7,8,9,10,11. Here we show that tunable optical elements fabricated from patterned plasmonic sheets with periodic kirigami cuts make possible the polarization modulation of terahertz radiation under application of mechanical strain. A herringbone pattern of microscale metal stripes enables a dynamic range of polarization rotation modulation exceeding 80° over thousands of cycles. Following out-of-plane buckling, the plasmonic stripes function as reconfigurable semi-helices of variable pitch aligned along the terahertz propagation direction. Several biomaterials, exemplified by an elytron of the Chrysina gloriosa, revealed distinct TCD fingerprints associated with the helical substructure in the biocomposite. Analogous kirigami modulators will also enable other applications in terahertz optics, such as polarization-based terahertz imaging, line-of-sight telecommunication, information encryption and space exploration.

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Fig. 1: Schematic of chiral kirigami topology.
Fig. 2: THz TDS measurement of a chiral kirigami modulator.
Fig. 3: Understanding the physical meaning of resonance frequency.
Fig. 4: Computed THz circular dichroism and time-averaged current norm distributions on the kirigami modulator with φ = 45°.
Fig. 5: Measurements of TCD using a kirigami chiroptical modulator.

Data availability

All relevant data that support our experimental findings are available from the corresponding author upon reasonable request.

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Acknowledgements

All the authors acknowledge support from the Defense Advanced Research Projects Agency (DARPA) project HR00111720067 ‘Electromagnetic Processes and Normal Modes in Bacterial Biofilms’. Parts of the work were also supported by the NSF projects ‘Energy- and Cost-Efficient Manufacturing Employing Nanoparticles’ (NSF 1463474) and ‘Multi-Scale Origami For Novel Photonics’ (NSF 071702). The authors also acknowledge financial and programmatic support from the University of Michigan College of Engineering’s Blue Sky Initiative, the UM Electron Microscopy Facility (MC)2 for its assistance with electron microscopy and NSF grant no. DMR-9871177 for funding of the JEOL 2010F analytical electron microscope used in this work. We acknowledge the Lurie Nanofabrication Facility for facilitating the fabrication of kirigami modulators.

Author information

W.J.C., G.C., T.B.N. and N.A.K. contributed to the design, data analysis and preparation of the manuscript. N.A.K. originated the concept. W.J.C. designed and fabricated the kirigami modulators and measured the mechanical responses. W.J.C. and G.C. performed the optical experiments and W.J.C., G.C. and Z.H. performed the simulations. S.Z. provided technical support for reconstruction of the 3D kirigami model. W.J.C., G.C., T.B.N. and N.A.K. planned and supervised the project.

Correspondence to Theodore B. Norris or Nicholas A. Kotov.

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Supplementary information

Supplementary Information

Supplementary methods, Supplementary Figs. 1–28, Supplementary video captions 1–2, Supplementary references 1–40

Supplementary Video 1

Video of stretching and release of kirigami chiroptical modulator (ε from 0 to 22.5%)

Supplementary Video 2

Video of the 3D topology of a reconstructed kirigami structure with 45° wire slant angle stretched by 13.5% strain

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Choi, W.J., Cheng, G., Huang, Z. et al. Terahertz circular dichroism spectroscopy of biomaterials enabled by kirigami polarization modulators. Nat. Mater. 18, 820–826 (2019). https://doi.org/10.1038/s41563-019-0404-6

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