Publication database
Subwavelength dielectric resonators for nonlinear nanophotonics
Bound states in the continuum (BICs) represent localized modes with energies embedded in the continuous spectrum of radiating waves. BICs were discovered initially as a mathematical curiosity in quantum mechanics, and more recently were employed in photonics. Pure mathematical bound states have infinitely-large quality factors (Q factors) and zero resonant linewidth. In optics, BICs are physically limited by a finite size, material absorption, structural disorder, and surface scattering, and they manifest themselves as the resonant states with large Q factors, also known as supercavity modes or quasi-BICs. Optical BIC resonances have been demonstrated only in extended 2D and 1D systems and have been employed for distinct applications including lasing and sensing. Optical quasi-BIC modes in individual nanoresonators have been discovered recently but they were never observed in experiment. Here, we demonstrate experimentally an isolated subwavelength nanoresonator hosting a quasi-BIC resonance. We fabricate the resonator from AlGaAs material on an engineered substrate, and couple to the quasi-BIC mode using structured light. We employ the resonator as a nonlinear nanoantenna and demonstrate record-high efficiency of second-harmonic generation. Our study brings a novel platform to resonant subwavelength photonics.
Third-order nonlinear optical properties of phycobiliproteins from cyanobacteria and red algae
Second hyperpolarizability (γ) measurements as well as third harmonic generation (THG) imaging was performed to determine if phycobiliproteins contribute to cyanobacteria THG, and to establish if phycobiliproteins are suitable dyes for THG microscopy. Three phycobiliproteins and one phycobilin were investigated via THG ratio γ measurements, revealing phycocyanobilin has ~7× higher γ than β-carotene, a standard THG dye. Phycobiliproteins also had large γ values, showing they are promising THG dyes. Stoichiometric summations of phycobilin γ values revealed they are the dominant source of THG signal from phycobiliproteins. THG imaging was performed to demonstrate phycobiliproteins and phycobilins can be useful THG dyes.