Chiroptical Kirigami Modulators for Terahertz Circular Dichroism Spectroscopy of Biomaterials

ABSTRACTSTerahertz circular dichroism (TCD) offers spectroscopic capabilities for understanding mesoscale chiral architecture and low-energy vibrations of macromolecules in (bio)materials1-5. However, the lack of dynamic polarization modulators comparable to polarization optics for other parts of electromagnetic spectrum impedes proliferation of TCD spectroscopy6-10. Here we show that tunable optical elements fabricated from patterned plasmonic sheets with periodic kirigami cuts make possible polarization modulation of THz radiation under application of mechanical strain. A herringbone pattern of microscale metal stripes enables dynamic range of polarization rotation modulation exceeding 80{degrees} over thousands of cycles. Upon out-of-plane buckling, the plasmonic stripes function as reconfigurable semi-helices of variable pitch aligned along the THz propagation direction. Several biomaterials, exemplified by elytrons of Chrysina gloriosa beetles, revealed distinct TCD fingerprints associated with the helical substructure in the biocomposite. Analogous kirigami modulators will also enable other applications in THz optics, such as polarization-based terahertz imaging and phase-encrypted telecommunication.