Practical design considerations and performance characteristics of high numerical aperture holographic lenses

The diffraction efficiency of interferometrically formed holographic lenses is influenced by the recording geometry and properties of the recording material. Variations in efficiency increase when attempting to make high numerical aperture elements. The factors which influence the diffraction efficiency of high numerical aperture holographic lenses are examined

Regional microglia are transcriptionally distinct but similarly exacerbate neurodegeneration in a culture model of Parkinson\u27s disease.

BACKGROUND: Parkinson\u27s disease (PD) is characterized by selective degeneration of dopaminergic (DA) neurons of the substantia nigra pars compacta (SN) while neighboring ventral tegmental area (VTA) DA neurons are relatively spared. Mechanisms underlying the selective protection of the VTA and susceptibility of the SN are still mostly unknown. Here, we demonstrate the importance of balance between astrocytes and microglia in the susceptibility of SN DA neurons to the PD mimetic toxin 1-methyl-4-phenylpyridinium (MPP METHODS: Previously established methods were used to isolate astrocytes and microglia from the cortex (CTX), SN, and VTA, as well as embryonic midbrain DA neurons from the SN and VTA. The transcriptional profile of isolated microglia was examined for 21 canonical pro- and anti-inflammatory cytokines by qRT-PCR with and without MPP RESULTS: We found that regionally isolated microglia (SN, VTA, CTX) exhibit basal differences in their cytokine profiles and that activation of these microglia with MPP CONCLUSION: These results suggest that the balance of astrocytes and microglia within the midbrain is a key factor underlying the selective vulnerability of SN DA neurons seen in PD pathogenesis and that VTA astrocytes mediate protection of DA neurons which can be countered by greater numbers of deleterious microglia

Use of rigorous vector coupled-wave theory for designing and tolerancing surface-relief diffractive components for magneto-optical heads

A rigorous coupled wave model is presented, experimentally validated, and used for tolerancing surface relief diffractive elements. Applications of the model in the design and tolerancing of components for magneto optical (M-O) data storage heads are investigated

Self-assembled aggregates of neutral nonlinear optical dyes in smectite clay films

The field of photonics relies on nonlinear optical (NLO) materials and their unique light interacting properties to guide and manipulate light for such uses as optical switches and optical data storage. Hybrid organic-inorganic composites offer excellent routes to such materials synthesis. We report herein the first study of neutral organic NLO chromophores adsorbed onto hectorite and laponite clay films. Seven different dyes (disperse red 1; disperse red 13; disperse red 19; disperse orange 3; disperse orange 13; disperse orange 25, and DANS, [4-dimethylamino-4\u27 -nitrostilbene]), and two exchangeable cations (sodium and zinc), are used to create the hybrid films. The nature of the dye aggregation is characterized using UV/VIS spectroscopy, Xray diffraction, and second harmonic generation (SHG). Both J and H type aggregates are observed. The type and extent of aggregation is found to be primarily dependent on the functionalized structure of the dye molecule. The relative populations of aggregating versus bulk dye is found to depend on the amount of available clay surface area, which is affected by host clay particle size and the intergallery cation charge density. J aggregation is maximized at 0.10 w/w% dye in the zinc-laponite system. We found that the overall maximum dye loading levels are above 10 w/w% for the laponite system and between 1 and 5 w/w% for hectorite. Laponite is more ideally suited for optical device applications given its low background absorption. Currently the composite films do not show any second harmonic generation even though J aggregates have been shown to exhibit enhanced SHG in related systems

Basin structure of optimization based state and parameter estimation

Most data based state and parameter estimation methods require suitable initial values or guesses to achieve convergence to the desired solution, which typically is a global minimum of some cost function. Unfortunately, however, other stable solutions (e.g., local minima) may exist and provide suboptimal or even wrong estimates. Here we demonstrate for a 9-dimensional Lorenz-96 model how to characterize the basin size of the global minimum when applying some particular optimization based estimation algorithm. We compare three different strategies for generating suitable initial guesses and we investigate the dependence of the solution on the given trajectory segment (underlying the measured time series). To address the question of how many state variables have to be measured for optimal performance, different types of multivariate time series are considered consisting of 1, 2, or 3 variables. Based on these time series the local observability of state variables and parameters of the Lorenz-96 model is investigated and confirmed using delay coordinates. This result is in good agreement with the observation that correct state and parameter estimation results are obtained if the optimization algorithm is initialized with initial guesses close to the true solution. In contrast, initialization with other exact solutions of the model equations (different from the true solution used to generate the time series) typically fails, i.e. the optimization procedure ends up in local minima different from the true solution. Initialization using random values in a box around the attractor exhibits success rates depending on the number of observables and the available time series (trajectory segment).Comment: 15 pages, 2 figure

Optical system storage design with diffractive optical elements

Optical data storage systems are gaining widespread acceptance due to their high areal density and the ability to remove the high capacity hard disk from the system. In magneto-optical read-write systems, a small rotation of the polarization state in the return signal from the MO media is the signal which must be sensed. A typical arrangement used for detecting these signals and correcting for errors in tracking and focusing on the disk is illustrated. The components required to achieve these functions are listed. The assembly and alignment of this complex system has a direct impact on cost, and also affects the size, weight, and corresponding data access rates. As a result, integrating these optical components and improving packaging techniques is an active area of research and development. Most designs of binary optic elements have been concerned with optimizing grating efficiency. However, rigorous coupled wave models for vector field diffraction from grating surfaces can be extended to determine the phase and polarization state of the diffracted field, and the design of polarization components. A typical grating geometry and the phase and polarization angles associated with the incident and diffracted fields are shown. In our current stage of work, we are examining system configurations which cascade several polarization functions on a single substrate. In this design, the beam returning from the MO disk illuminates a cascaded grating element which first couples light into the substrate, then introduces a quarter wave retardation, then a polarization rotation, and finally separates s- and p-polarized fields through a polarization beam splitter. The input coupler and polarization beam splitter are formed in volume gratings, and the two intermediate elements are zero-order elements

Application of holographic optical elements to magneto-optic read/write heads

Objectives of this research are to determine the theoretical and practical performance limits of holographic optical elements (HOE's) formed in different recording materials, and to evaluate the application of these components to magneto-optic read/write heads