We experimentally and theoretically study nonlinear vortex dynamics with propagation by encoding vortices into a laser beam and propagating the beam through a tank filled with methanol and carbon dust. The fluid medium allows variable path length through the tank and provides a repulsive third-order nonlinear photon-photon interaction via its thermo-optic coefficient. The emerging mode is imaged onto a CCD and interfered with a reference beam allowing measurement of amplitude and phase information by single-shot interferometry. We observed core sharpening and suppression of the annihilation of oppositely charged vortices consistent with our theoretical predictions. The repulsive third-order nonlinearity of the medium gives a direct mathematical analogy between nonlinear propagation of light and mean-field dynamics of quantum fluids.
Entangled two-photon dynamics offer a rich manifestation of the interplay between geometry and information. Such states accumulate a geometric phase that is not equal to the sum of those of the associated single-photon states, the difference amounting to a Geometric Phase of Entanglement (GPE). A functional relationship is derived between the GPE and reduced state entropies, showing that geometric phase measured for one photon will exhibit a quantum correlation with that of the other photon. This is explored within the setting of Type-I, collinear spontaneous parametric down-conversion, where two-photon states can be represented as a sum of spatially-entangled Laguerre-Gaussian modes.
We propose a method to controllably create free-space, “hard-trapped” two-dimensional fluids with Bessel-Gaussian beam superpositions. We use these systems to experimentally demonstrate several vortex dynamics that resemble dynamics numerically predicted in weakly-interacting quantum fluids. Theoretically, we perform a Bessel-mode decomposition on an initial state containing an arrangement of optical vortices. The experiment is performed using a laser beam that is structured holographically with a spatial light modulator that contains the initial condition of the reconstructed field from the theoretical decomposition. This works allows for the experimental verification of many numerically predicted dynamics or the discovery of new dynamics from experiment.
Solid-state energy upconversion has many potential applications, from nonlinear photonics and biophotonics to expanding the spectrum available for solar energy harvest. In organic molecular systems, upconversion is frequently done in solution to mitigate aggregation-induced photoluminescence quenching or to facilitate the diffusion of triplet donors in Triplet-Triplet Annihilation (TTA) systems. Here we demonstrate an organic thin film upconversion system utilizing two-photon absorption (TPA) properties to improve upconversion efficiency. In blend films of Stilbene-420 and Rhodamine 6G we observe a tenfold increase in up-converted fluorescence compared to the fluorescence yield of TPA in pristine stilbene films. While TPA normally has quadratic dependence on excitation intensity, these blend films exhibit sub-quadratic intensity dependence, indicating a combination of linear and quadratic upconversion processes and dramatically improving upconversion efficiency at lower excitation intensities. This improvement in intensity dependence allows for relatively efficient upconversion upon excitation by a nanosecond laser pulse, in contrast to the more expensive femtosecond lasers generally required for excitation in TPA microscopy and similar systems. Time-resolved photoluminescence decay measurements reveal that all excited states involved in this upconversion process are singlets, which indicates the potential for reduced energy losses when compared to TTA upconversion systems and their inherent intersystem-crossing energy losses. We observe emission from both the Rhodamine 6G donor molecules and Stilbene-420 acceptor molecules, indicating the presence of prompt fluorescence from the donor as well as upconversion to the acceptor, and FRET losses from acceptor back to donor. By fitting to a kinetic model we extract rates for these competing processes.
Group IV clathrates are a unique class of guest/framework type compounds that are considered potential candidates for a wide range of applications (superconductors to semiconductors). To date, most of the research on group IV clathrates has focused heavily on thermoelectric applications. Recently, these materials have attracted attention as a result of their direct, wide band gaps for possible use in photovoltaic applications. Additionally, framework alloying has been shown to result in tunable band gaps. In this review, we discuss the current work and future opportunities concerning the synthesis and optical characterization of group IV clathrates for optoelectronics applications.
Millimeter wave reflectometry offers a noncontact means of measuring the thicknesses of individual layers within multi-layer dielectric coatings on metallic substrates. Complex reflection coefficients of both TM and TE/TM waves incident on coated materials are measured over a range of frequencies and grazing angles of incidence. The sensitivity of the apparatus is such that single-layer coatings differing by 0.2 microns can be distinguished.
An intuitive deconvolution algorithm known s CLEAN is considered as a means of improving images associated with microwave nondestructive evaluation (NDE). Flawed metallic surfaces are scanned using a continuous wave (cw), X-band synthetic aperture radar (SAR), and images are produced using a synthetic-aperture focusing algorithm. The results are compared with those obtained by further processing the data using the CLEAN algorithm. The utility of adopting such a scheme to improve flaw detection is discussed.
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