Nonlinear self-action of light through biological suspensions

It is commonly thought that biological media cannot exhibit an appreciable nonlinear optical response. We demonstrate, for the first time to our knowledge, a tunable optical nonlinearity in suspensions of cyanobacteria that leads to robust propagation and strong self-action of a light beam. By deliberately altering the host environment of the marine bacteria, we show experimentally that nonlinear interaction can result in either deep penetration or enhanced scattering of light through the bacterial suspension, while the viability of the cells remains intact. A theoretical model is developed to show that a nonlocal nonlinearity mediated by optical forces (including both gradient and forward-scattering forces) acting on the bacteria explains our experimental observation

Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions

Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.Comment: 20 Pages, 5 figures, accepted for publication in Light, Science & Applicatio

Investigation of the Role of Trap States in Solar Cell Reliability using Photothermal Deflection Spectroscopy

Stability and reliability of solar cells are crucial for utilizing them for solar energy technology. In this dissertation work photothermal deflection spectroscopy (PDS) technique was used to detect small absorption changes and to investigate trap density changes in three different types of solar cells in the process of light, air, and temperature induced degradation. The light-induced metastable changes in the properties of amorphous silicon and crystallinity effect in microcrystalline silicon were quantified by PDS. The effect of ligands and nanoparticle (NP) size on mid-gap trap states in NP thin films (CdTe and PbS) as it impacts on the performance during degradation were examined. Finally, several most common polymers (P3HT, MEH-PPV, and Polyfluorene Red) films absorption were compared and effect of photo-degradation and photo-oxidation on their trap states were analyzed. The PDS measurement technique is independent of scattering and permits the full band gap of the solar cells to be measured as well as the Urbach energy and the density of mid-gap trap states through analysis of the band gap and the band tail absorption. This work demonstrated that the higher amount of trap states in the material do not necessary limit the efficiency of a solar cell, since material structure, crystallinity, a particle deformation, and a polymer's decomposition may have much higher effect on the solar cells' stability and performance

Investigation of the Role of Trap States in Solar Cell Reliability using Photothermal Deflection Spectroscopy

Stability and reliability of solar cells are crucial for utilizing them for solar energy technology. In this dissertation work photothermal deflection spectroscopy (PDS) technique was used to detect small absorption changes and to investigate trap density changes in three different types of solar cells in the process of light, air, and temperature induced degradation. The light-induced metastable changes in the properties of amorphous silicon and crystallinity effect in microcrystalline silicon were quantified by PDS. The effect of ligands and nanoparticle (NP) size on mid-gap trap states in NP thin films (CdTe and PbS) as it impacts on the performance during degradation were examined. Finally, several most common polymers (P3HT, MEH-PPV, and Polyfluorene Red) films absorption were compared and effect of photo-degradation and photo-oxidation on their trap states were analyzed. The PDS measurement technique is independent of scattering and permits the full band gap of the solar cells to be measured as well as the Urbach energy and the density of mid-gap trap states through analysis of the band gap and the band tail absorption. This work demonstrated that the higher amount of trap states in the material do not necessary limit the efficiency of a solar cell, since material structure, crystallinity, a particle deformation, and a polymer's decomposition may have much higher effect on the solar cells' stability and performance

Self-trapping and flipping of double-charged vortices in optically induced photonic lattices

We report what is believed to be the first observation of self-trapping and charge-flipping of double-charged optical vortices in two-dimensional photonic lattices. Both on-and off-site excitations lead to the formation of rotating quasi-vortex solitons, reversing the topological charges and the direction of rotation through a quadrupolelike transition state. Experimental results are corroborated with numerical simulations

Experiments On Gaussian Beams And Vortices In Optically Induced Photonic Lattices

We investigate experimentally the propagation of fundamental Gaussian beams and vortices in a two-dimensional photonic lattice optically induced with partially coherent light. We focus on soliton-lattice interactions and vortex-lattice interactions when the lattice is operated in a nonlinear regime. In this case a host of novel phenomena is demonstrated, including soliton-induced lattice dislocation-deformation, soliton hopping and slow-down, and creation of structures akin to optical polarons. In addition, we observe that the nonlinear interaction between a vortex beam and a solitonic lattice leads to lattice twisting due to a transfer of the angular momentum carried by the vortex beam to the lattice. Results demonstrating a clear transition from discrete diffraction to the formation of two-dimensional, discrete fundamental and vortex solitons in a linear lattice are also included. © 2005 Optical Society of America

High Spatiotemporal Resolution Imaging with Localized Plasmonic Structured Illumination Microscopy.

Localized plasmonic structured illumination microscopy (LPSIM) provides multicolor wide-field super-resolution imaging with low phototoxicity and high-speed capability. LPSIM utilizes a nanoscale plasmonic antenna array to provide a series of tunable illumination patterns beyond the traditional diffraction limit, allowing for enhanced resolving powers down to a few tens of nanometers. Here, we demonstrate wide-field LPSIM with 50 nm spatial resolution at video rate speed by imaging microtubule dynamics with low illumination power intensity. The design of the LPSIM system makes it suitable for imaging surface effects of cells and tissues with regular sample preparation protocols. LPSIM can be extended to much higher resolution, representing an excellent technology for live-cell imaging of protein dynamics and interactions