RESUMO
The nonlinear optical properties of low-dimensional polycrystalline halide perovskite films consisting of ethylammonium (EA) and butylammonium (BA) cations are investigated using Z-scan technique. Across the band-edge, two-dimensional (BA)2PbI4 exhibits a transition from saturable absorption (SA) to reverse-SA and its nonlinear absorption and nonlinear refractive index are much smaller than those of bulk counterparts. Meanwhile, EAPbI3 with one-dimensionality of the inorganic structure shows the SA behavior both above and below band-edge and the estimated nonlinear optical parameters of polycrystalline EAPbI3 are comparable to those of single-crystalline ones, attributed to high dielectric contrast between the inorganic and organic elements in one-dimensional structures.
RESUMO
Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS2)/aluminum metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin-orbit interaction.
