ABSTRACT
We report on experiments with Möbius strip microlasers, which were fabricated with high optical quality by direct laser writing. A Möbius strip, i.e., a band with a half twist, exhibits the fascinating property that it has a single nonorientable surface and a single boundary. We provide evidence that, in contrast to conventional ring or disk resonators, a Möbius strip cavity cannot sustain whispering gallery modes (WGM). Comparison between experiments and 3D finite difference time domain (FDTD) simulations reveals that the resonances are localized on periodic geodesics.
ABSTRACT
Short peptides made from repeating units of phenylalanine self-assemble into a remarkable variety of micro- and nanostructures including tubes, tapes, spheres, and fibrils. These bio-organic structures are found to possess striking mechanical, electrical, and optical properties, which are rarely seen in organic materials, and are therefore shown useful for diverse applications including regenerative medicine, targeted drug delivery, and biocompatible fluorescent probes. Consequently, finding new optical properties in these materials can significantly advance their practical use, for example, by allowing new ways to visualize, manipulate, and utilize them in new, in vivo, sensing applications. Here, by leveraging a unique electro-optic phase microscopy technique, combined with traditional structural analysis, it is measured in di- and triphenylalanine peptide structures a surprisingly large electro-optic response of the same order as the best performing inorganic crystals. In addition, spontaneous domain formation is observed in triphenylalanine tapes, and the origin of their electro-optic activity is unveiled to be related to a porous triclinic structure, with extensive antiparallel beta-sheet arrangement. The strong electro-optic response of these porous peptide structures with the capability of hosting guest molecules opens the door to create new biocompatible, environmental friendly functional materials for electro-optic applications, including biomedical imaging, sensing, and optical manipulation.
ABSTRACT
The unique optical properties of arrays of metallic nanoparticles are of great interest for many applications such as in optical data storage, sensing applications, optoelectronic devices or as platforms to increase the detection limit in spectroscopic measurements. Nonlinear optical phenomena can also be altered by metallic nanostructures opening new possible applications. In this work, arrays composed of non-centrosymmetric individual structures with three fold axial symmetry made of gold are designed and fabricated using electron beam lithography. The nonlinear optical properties of these structures are investigated using second-harmonic generation microscopy (SHGM) with a femtosecond excitation source set near the plasmon resonance frequency. Modeling of the electromagnetic field distribution around the metallic structures is performed using the Finite Difference Time Domain (FDTD) method, highlighting the confinement of the SHG signal and its polarization dependence. Polarization-resolved measurements are conducted to correlate the SHG signal with the structure and symmetry of the individual nanostructures. Since both two-photon induced photoluminescence (TPPL) and SHG signals are produced upon excitation of these structures, lifetime measurements are performed to further evaluate the magnitude of these two effects.
ABSTRACT
Cuboid-shaped organic microcavities containing a pyrromethene laser dye and supported upon a photonic crystal have been investigated as an approach to reducing the lasing threshold of the cavities. Multiphoton lithography facilitated fabrication of the cuboid cavities directly on the substrate or on the decoupling structure, while similar structures were fabricated on the substrate by UV lithography for comparison. Significant reduction of the lasing threshold by a factor of ~30 has been observed for cavities supported by the photonic crystal relative to those fabricated on the substrate. The lasing mode spectra of the cuboid microresonators provide strong evidence showing that the lasing modes are localized in the horizontal plane, with the shape of an inscribed diamond.
