Nonlinear absorption and nonlinear refraction: Maximizing the merit factors

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications

TLR3-mediated apoptosis and activation of phosphorylated Akt in the salivary gland epithelial cells of primary Sjögren’s syndrome patients

This study aimed at ascertain whether innate immunity is involved in the apoptosis of primary cultured salivary gland epithelial cells (SGECs) in primary Sjögren\u27s syndrome (pSS). Induction of apoptosis of SGECs was performed using a TLR3 ligand, poly (I:C). Activation of phosphorylated-Akt (pAkt) and cleaved-caspase 3 was determined by Western blotting or immunofluorescence. Expression of TLR2 and TLR3 with pAkt was observed in cultured SGECs after 24-h stimulation with each ligand. Compared with stimulation with the peptidoglycan or lipopolysaccharide, that with poly (I:C) induced significant nuclear fragmentation, as determined by Hoechst staining (p = 0.0098). Apoptosis was confirmed by terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) staining of SGECs from pSS patients and a normal subject. A significant increase in TUNEL-positive cells was observed by the addition of a PI3K inhibitor, LY294002. Poly (I:C) phosphorylated stress-activated protein kinase/Jun-terminal kinase and p44/42 MAP kinase as well as Akt. Furthermore, poly (I:C)-induced caspase 3 cleavage in SGECs was also inhibited by LY294002. Similar results were obtained using SGECs obtained from a normal subject. The results demonstrated for the first time that TLR3 induces the apoptotic cell death of SGECs via the PI3K-Akt signaling pathway

Lattice Resonances in Optical Metasurfaces with Gain and Loss

Periodic lattices of strongly scattering objects coupled to active media are of central importance in applied nanophotonics, serving as light-emitting metasurfaces of tailored emission properties and promising an attractive platform for testing novel physical concepts and realization of unprecedented light-shaping functions. We provide an overview of the semianalytical Green function method with Ewald lattice summation applied to the investigation of surface lattice resonances in periodic arrays of resonant nanoscatterers with gain and loss. This theory is meant as a minimal model for plasmonic lattices and metasurfaces with gain: minimal in complexity, yet sufficiently rich to be a self-consistent, fully retarded multiple scattering model. It enables to include the electromagnetic interactions between electric and/or magnetic point dipoles of arbitrary orientation and arrangement, taking into account retardation and tensorial nature of these interactions and including radiation damping. It gives access to the far-field observables (reflection/transmission), as well as to the photonic band structure of guided modes. At the same time, it does not violate the optical theorem, as opposed to the commonly used tight-binding or quasi-static models. After extending the lattice Green function formalism to include gain and loss in the unit cell, we demonstrate the effects of parity-time (PT) symmetry breaking in active-lossy plasmonic arrays: the emergence of exceptional points, nontrivial topology of photonic bands, diverging effective unit-cell polarizability, and spin polarization in the PT-broken phase

Trapping light in resonant metasurfaces for plasmon lasing

Mitigating radiative losses in resonant structures has been a target of extensive research in photonics, involving various concepts such as optical dark states, multipoles, anapoles, embedded eigenstates, as well as momentum- or symmetry-mismatched lattice resonances in periodic systems. Here, we explore the possibility of improving the quality factors of dispersive lattice resonances within the light cone of a plasmonic metasurface. In particular, we find that antisymmetric modes of a honeycomb lattice of isotropic metal nanoparticles have symmetry-protected degenerate band edges, whereas the same lattice composed of anisotropic nanoparticles has an off-normal bound state along one of the dispersive bands. In addition to theoretical calculations, we also present our preliminary experimental results on distributed feedback lasing in such systems

Universal scaling in the dynamic hysteresis, and non-Markovian dynamics, of a tunable optical cavity

We investigate, experimentally and theoretically, the dynamics of a laser-driven cavity with noninstantaneous effective photon-photon interactions. Scanning the laser-cavity frequency detuning at different speeds across an optical bistability, we find a hysteresis area that is a nonmonotonic function of the speed. In the limit of fast scans comparable to the memory time of the interactions, we demonstrate that the hysteresis area decays following a universal power law with scaling exponent -1. We further demonstrate a regime of non-Markovian dynamics emerging from white noise. This regime is evidenced by peaked distributions of residence times in the metastable states of our system. Our results offer new perspectives for exploring the physics of scaling, universality, and metastability, in non-Markovian regimes using arrays of bistable optical cavities with low quality factors, driven by low laser powers, and at room temperature