Search

Electrically polarizable micro- and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant resistor–inductor–capacitor (RLC) circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning, and linewidth can be continuously varied by changing the supply voltage, supply frequency, and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator, the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single-cell and biochemical reaction analysis.

This article presents a general way to enable automatic generation of digitized laboratories (a sort of digital twin for laboratory experimental setups) from remote laboratories and their easy deployment and publication. To demonstrate its effectiveness, we use two existing tools to generate and publish two digitized laboratories online from two implementations of a Snell's law remote laboratory, although they could be applied to many other remote laboratories. The first of these tools is a communication protocol that was designed to manipulate laboratory equipment through the Internet. This protocol can be used to automatically loop through different possible laboratory states and store them. The second one is a web platform that allows uploading files, that contain data sets of the laboratory states, to publish the digitized laboratory as a web application that is generated automatically.

Trapping and manipulation of micro and nanoparticles are essential functional elements of lab-on-a-chip and micro total analysis systems with applications ranging from single cell analysis, diagnostics, drug discovery, and chemical synthesis. Reliable optical trapping of subwavelength particles is difficult due to the diffraction limited gradient of the optical intensity. Near-field traps have emerged as excellent systems to overcome this bottleneck. Using a periodic arrangement of C-shaped apertures we demonstrate the on-chip manipulation of single sub-wavelength polystyrene beads. The wavelength and polarization sensitivity of these resonant nanostructures is exploited to expose the trapped bead to a time varying near-field force using wavelength and polarization multiplexing schemes. While optical trapping has the advantage of being contactless, dielectrophoresis provides higher forces due to the flexibility of applying larger voltages and field gradients. The RF/Microwave frequency regime where dielectrophoresis operates allows increased polarizability of certain samples due to contribution from orientational, molecular and atomic polarizations as well as particle’s electrical conductivity. Combining the above advantages of both the techniques we discuss photoinduced dielectrophoretic trapping and manipulation of nanoparticles. Using dielectrophoretic trapping we discuss the simultaneous manipulation of beads and droplets as a route for on chip chemical synthesis.

X-ray imaging by means of a grating-based Talbot-Lau interferometer has become an important tool for a wide variety of application areas such as security, medical and materials analysis. Imaging modalities include attenuation, differential phase contrast, and visibility contrast (or so-called dark field). We have developed a novel modeling approach based on ray tracing with commercially available software (Zemax OpticStudio) that yields image projections for all three modalities. The results compare favorably with experimental findings. Our polychromatic ray-based model accommodates realistic 3-D CAD objects with tailored materials properties and also allows for both surface and bulk scattering. As such, the model can simulate imaging of complicated objects as well as assist in a physical understanding of experimental projection details.

Ultraviolet decontamination of personal protective equipment, particularly masks, is important in situations where mask reuse is practiced. To assist in the development of UV-C decontamination chambers, we have constructed ray tracing models in Zemax OpticStudio v20.1 for two distinct geometries, namely, a rectangular cabinet and a cylindrical can. These models provide irradiance distributions that can be used for comparison with experiment, as well as to predict local irradiance variation over the surface of a mask. In this paper we describe the model details, including: (1) a mask object in CAD format; (2) our assumptions for modeling surface properties; (3) the use of polygon object detectors for local irradiance analysis; and (4) experimental results that compare favorably to the simulations.

A grating-based Talbot-Lau X-ray interferometer provides three imaging modalities, namely attenuation, differential phase contrast, and dark field. Of these, dark-field imaging is uniquely capable of detecting and characterizing micron-scale fine structure in an object via small-angle scattering that reduces fringe visibility. In Part 1 [Opt. Express 29, 40891 (2021)10.1364/OE.447794], we formulate a statistical optics model that predicts the change in visibility, or dark-field signal, as a function of the statistical properties of the scattering object as well as its location within the interferometer. In Part 2, we demonstrate use of this model by simulating an object comprising a random collection of scattering microspheres placed in an X-ray grating interferometer designed to operate at 28 keV. The statistical optics results are validated by numerical Fourier optics simulations.

A grating-based Talbot-Lau X-ray interferometer provides three imaging modalities, namely attenuation, differential phase contrast, and dark field. Of these, dark-field imaging is uniquely capable of detecting and characterizing micron-scale fine structure in an object via small-angle scattering that reduces fringe visibility. Several empirical studies have been published showing the utility of this imaging modality for a wide range of applications. There also exists a more limited set of theoretical papers, based primarily on wave-optics formulations. In this two-part paper we present a comprehensive statistical optics model of the dark-field effect. In Part 1, we develop the theoretical underpinnings of the model with an emphasis on a scattering object comprising a random collection of microspheres, and in Part 2 [Opt. Express 29, 40917 (2021)10.1364/OE.447798], we provide a variety of example simulation results.

We present a device that can achieve controlled transport of colloidal microparticles using an array of micro-electrodes. By exciting the micro-electrodes in regular sequence with an AC voltage, a time-varying moving dielectrophoretic force-field is created. This force propels colloidal microparticles along the electrode array. Using this method, we demonstrate bidirectional transport of polystyrene micro-spheres. Electromagnetic simulation of the device is performed, and the dielectrophoretic force profile around the electrode array is mapped. We develop a Brownian dynamics model of the trajectory of a particle under the influence of the time-varying force-field. Numerical and experimental results showing controlled particle transport are presented. The numerical model is found to be in good agreement with experimental data. The developed numerical framework can be useful in designing and modeling lab-on-a-chip devices that employ external non-contact forces for micro-/nanoparticle manipulation.

Typical x-ray detectors have a fundamental trade-off between resolution and quantum efficiency (QE). High quantum efficiency x-ray detection requires a thick conversion medium, but decreases the resolution due to limited pixel aspect ratios for both direct and indirect x-ray detection. We present a method for x-ray detection, holographic x-ray detection, which uses photorefractive materials to create a high resolution and high efficiency detector. The x-ray image is recorded in the volume of the photorefractive material, bypassing the aspect ratio issue of typical x-ray detectors. Holographic x-ray detection operates in three stages: recording an x-ray hologram in a photorefractive crystal, reading the hologram with visible light, and then erasing the hologram using ultraviolet light. We have experimentally demonstrated holographic x-ray detection with a resolution of 208 lp/mm (80% QE at 40 keV), an order of magnitude resolution improvement over commercially available x-ray detectors while maintaining > 80% QE.

We present evidence-based design principles for three different UV-C based decontamination systems for N95 filtering facepiece respirators (FFRs) within the context of the SARS-CoV-2 outbreak of 2019–2020. The approaches used here were created with consideration for the needs of low- and middle-income countries (LMICs) and other under-resourced facilities. As such, a particular emphasis is placed on providing cost-effective solutions that can be implemented in short order using generally available components and subsystems. We discuss three optical designs for decontamination chambers, describe experiments verifying design parameters, validate the efficacy of the decontamination for two commonly used N95 FFRs (3M, #1860 and Gerson #1730), and run mechanical and filtration tests that support FFR reuse for at least five decontamination cycles.

Educating peers and broader audiences is of great significance within the scientific community. The education process aids the communication of ideas and allows for engagement with science. We present a ready-to-use tool to exchange data collected in laboratories in a scalable, graphical and easily accessible manner using Massively Scalable Online Laboratories (MSOL) embedded within Virtual Interactive Scalable Online Notebooks for Science (VISONS). The tool we present replicates the experiment in a visual and interactive way, dynamically displaying the experiment in all of its states. Using VISONS, researchers can more easily engage in discussions about their experimental results, which allows for a deeper understanding of their data and scientific challenges. The form of data exchange and graphic interface we present here helps to stimulate purposeful conversations about cutting-edge science by using VISONS during discussions with peers or in publications. Moreover, our approach, which uses efficient data storage and retrieval capabilities, provides scalable data management that laboratory environments currently lack. Simultaneously, we provide a more effective way for researchers manage their own work. VISONS offer a clear and concise version control system, assisting scientists at all stages of the development process. To provide information security during preliminary experimental work, before official publications, we incorporated a feature to choose the target audience for each experiment. To demonstrate the merits of VISONS, we recorded different versions of a cutting-edge science experiment, a quantum-noise limited differential phase contrast X-Ray imaging system, during its development process.

A method for efficiently trapping nanoparticles using a dielectrophoresis (DEP)-assisted plasmonic trap is presented. The proposed method overcomes the range limitations of a conventional plasmonic trap by employing a long-range DEP force to draw a nanoparticle closer to the plasmonic trap. To create the plasmonic trap, a $\mathsf{C}$-shaped engraving is used as it can trap a nanoparticle in a very small volume near the surface. A nanopillar is selected as the electrode to generated the DEP force as its height allows the force to extend further away from the surface. Extensive numerical simulations are performed to evaluate the performance improvement of the proposed scheme over conventional plasmonic trapping methods. The simulations show that the proposed scheme increases the probability of a successful trapping event by a factor of approximately three.

This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray imaging systems. Our experimental results demonstrate the rotational precision capabilities of the reported alignment system down to 0.42 mrad around the optical axis and 0.03 mrad around the axes perpendicular to the optical axis. The translational precision of 83.64 μ m along the optical axis and 1.22 μ m along the axes perpendicular to the optical axis is also demonstrated.This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray ...

We propose a method for peristaltic transport of nanoparticles using the optical force field over a nanostructured surface. Nanostructures may be designed to produce strong near-field hot spots when illuminated. The hot spots function as optical traps, separately addressable by their resonant wavelengths and polarizations. By activating closely packed traps sequentially, nanoparticles may be handed off between adjacent traps in a peristaltic fashion. A linear repeating structure of three separately addressable traps forms a "nano-optical conveyor belt"; a unit cell with four separately addressable traps permits controlled peristaltic transport in the plane. Using specifically designed activation sequences allows particle sorting.

Optical tweezers have been widely used to manipulate biological and colloidal material, but the diffraction limit of far-field optics makes focused beams unsuitable for manipulating nanoscale objects with dimensions much smaller than the wavelength of light. While plasmonic structures have recently been successful in trapping nanoscale objects with high positioning accuracy, using such structures for manipulation over longer range has remained a significant challenge. In this work, we introduce a conveyor belt design based on a novel plasmonic structure, the resonant C-shaped engraving (CSE). We show how long-range manipulation is made possible by means of handoff between neighboring CSEs, and we present a simple technique for controlling handoff by rotating the polarization of laser illumination. We experimentally demonstrate handoff between a pair of CSEs for polystyrene spheres 200, 390, and 500 nm in diameter. We then extend this technique and demonstrate controlled particle transport down a 4.5 μm long "nano-optical conveyor belt."

Nanoparticles trapped on resonant near-field structures engraved on a metallic substrate experience forces due to the engravings, as well as the image-like interaction with the substrate. In the case of normally incident optical excitation, the force due to the substrate is solely perpendicular to its surface. Numerical simulations are presented to demonstrate that under the combined influence of the aforementioned forces, a plasmonic nanoparticle can be repelled from the engraving along the substrate, while attracting it towards the substrate along its normal. This behavior can be achieved over a range of excitation wavelengths of the short wavelength mode of the coupled particle-substrate-trap system. To the best of our knowledge, this is the first illustration of an in-plane near-field optical barrier on a chip. The barrier is stable against resistive heating of the nanoparticle, as well as the induced non-isothermal flow. The wavelength-dependent switch between the proposed in-plane potential barrier and the stable potential well can pave the way for the gated transport of single nanoparticles, while holding them bound to the chip.

In this review, an overview of the subwavelength confinement of light with plasmonics is presented. Among the varieties of state-of-the-art technologies on this intensively-studied topic, we focus on the surface plasmon-assisted light enhancement via the single metallic aperture. Based on a systematic overview of the physical principles of light enhancement in subwavelength-sized metallic apertures, we investigate various types of apertures and discuss their characteristics.

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and limits the resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

We present a method for obtaining accurate numerical design sensitivities for metal-optical nanostructures. Adjoint design sensitivity analysis, long used in fluid mechanics and mechanical engineering for both optimization and structural analysis, is beginning to be used for nano-optics design, but it fails for sharp-cornered metal structures because the numerical error in electromagnetic simulations of metal structures is highest at sharp corners. These locations feature strong field enhancement and contribute strongly to design sensitivities. By using high-accuracy FEM calculations and rounding sharp features to a finite radius of curvature we obtain highly-accurate design sensitivities for 3D metal devices. To provide a bridge to the existing literature on adjoint methods in other fields, we derive the sensitivity equations for Maxwell’s equations in the PDE framework widely used in fluid mechanics.

CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand 80 MV/m fields without breaking down or emitting dark current. They can operate in 2×10^{−9} torr vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

We performed a parametric study to suppress secondary phases in lithium niobate thin films by using pulsed laser deposition (PLD). By reducing the growth rate and changing the ambient gas pressure respectively, we found that the main parameter suppressing secondary phases is controlling the plume strength. For investigating the relation between film phases and the plume strength, extensive parametric studies were performed by changing the oxygen ambient pressure, the target to substrate distance, and also the Li content in the target. The surface morphologies of single phase films obtained with different deposition parameters are compared and deposition parameters to achieve lower loss single-phase films are discussed.

In the implementation of most resolution enhancement techniques for optical lithography, full 3D simulation of effects such as topography imbalance in phase masks can be successfully modeled. However, these simulators do not appear to capture the full range of effects that impact the transmission of light through conducting (or partially conducting) films. In particular, certain resonant sub-wavelength geometric shapes, such as the C-aperture in a metallic conducting film, have been shown to have transmission values that are factors of 10^3-10^5 higher than simple geometric projections would predict. Using a new finite difference time domain solver that explicitly includes internal currents and analyzes the Poynting vector behavior of the EM fields, we can better understand the complex behavior of these resonant apertures. The currents are highly dependent on the polarization of the incoming EM excitation, as is the extraordinary transmission. We have also applied this in a limited fashion to geometries such as those expected to appear on photomasks in the 45nm node, when not extraordinary transmission but extraordinary opacity is predicted. These effects are also highly polarization dependent.

In this paper, we report the effects of direct-write e-beam parameters on achieving sub-micron periodic domain structures in homoepitaxial liquid phase epitaxy (LPE) LiNbO 3 thin films. We have studied the effects of the e-beam acceleration voltage, the areal dose, and the scanning speed on the domain structure regularity, and we have obtained optimal conditions for achieving improved structures. The most regular structures appear at acceleration voltages higher than 20 kV and areal dose ranges of 350–450 μC/cm 2 with lower scanning speeds. Under these optimal conditions we have fabricated approximately 500 μm-long gratings with 1.1 μm periods consisting of ∼180 nm domains. By simulating the optical reflectance based on a transfer matrix analysis, we have shown that the grating has a reflectance close to that of a perfect grating, in spite of the existence of stitching errors. The results indicate that using this fabrication approach, a switchable Bragg filter for optical communications may be fabricated by direct-write e-beam sub-micron domain engineering in LPE LiNbO 3 .

We have demonstrated sub-micron domain (∼200 nm) structures with a period ∼750 nm and ∼1.2 μm in liquid phase epitaxy (LPE) LiNbO3 films on congruent LiNbO3 substrates by using the direct-write e-beam domain engineering method. In comparison with single crystal congruent LiNbO3 (CLN) and stoichiometric LiNbO3 (SLN), we show that LPE LiNbO3 (LPE LN) is the most promising material for producing superior domain regularities and finer domain sizes than single crystals. A physical model is presented to qualitatively explain the observed differences in structure and regularity of the induced periodic domains among the three different materials we studied. We postulate that the higher Li/Nb ratio in LPE LN than in CLN enhances domain inversion initiation. Also, we believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.

In this paper, we discuss fundamental issues underlying holographic data storage: grating formation, recording and readout of thick and thin holograms, multiplexing techniques, signal-to-noise ratio considerations, and readout techniques suitable for conventional, phase conjugate, and associative search data retrieval. Next, we consider holographic materials characteristics for digital data storage, followed by a discussion on photorefractive media, fixing techniques, and noise in photovoltaic and other media with a local response. Subsequently, we discuss photopolymer materials, followed by a discussion on system tradeoffs and a section on signal processing and en/decoding techniques, succeeded by a discussion on electronic implementations for control, signal encoding, and recovery. We proceed further by presenting significant demonstrations of digital holographic systems. We close by discussing the outlook for future holographic data storage systems and potential applications for which holographic data storage systems would be particularly suited.

Cyberlab is a fully automated, Internet accessible laboratory for use in research and teaching, developed at Stanford University since 1996. Cyberlab is a completely self-contained system including a web-based scheduler, analysis tools, a data acquisition system, a digital notebook, extensive collaboration tools including simultaneous access to the equipment by multiple students, extensive security features, including firewall compliance without the need for IT intervention. The system is easily scalable and can be integrated with other distance learning programs.

We demonstrate the controlled transport of simultaneous nano-scale particles across a gold film patterned with nanopillars and C-shaped engravings. Nanopillars load particles onto nearby plasmonic conveyor belts formed from sequences of C-shaped engravings.

We transport nano-scale objects across a distance of many microns using a repeated sequence of rotated C-shaped plasmonic resonators. Rotating the polarization angle of the overhead laser illumination drives the particles' motion.

Near-field optical data storage systems are important for ultrahigh density data storage. One type of near-field optical data storage system uses a planar nano-aperture to define the data storage resolution. However, conventional nano-apertures have a tradeoff between resolution and power throughput. Recently, we reported a novel "C"-aperture design to overcome this problem. In this paper, we present our study on the mechanisms for power throughput enhancement, based on a detailed study of nano-slits using numerical simulations. We find that generating a propagation mode is essential for high power throughput, and by optimizing the design of the aperture thickness, resonant transmission can be achieved for even higher power throughput.

A semi-analytical model is proposed to describe the force generated by a near-field optical trap. The model contains fitting parameters that can be adjusted to resemble a reference force-field. The model parameters for a plasmonic near-field trap consisting of a C-shaped engraving are determined using least squares regression. The reference values required for the regression analysis are calculated using the Maxwell stress tensor method. The speed and accuracy of the proposed model are compared with the conventional method. The model is found to be significantly faster with an acceptable level of accuracy.

Nanoparticles trapped on resonant near-field apertures/engravings carved in plasmonic films experience optical forces due to the steep intensity gradient field of the aperture/engraving as well as the image like interaction with the substrate. For non-resonant nanoparticles the contribution of the substrate interaction to the trapping force in the vicinity of the trap (aperture/engraving) mode is negligible. But, in the case of plasmonic nanoparticles, the contribution of the substrate interaction to the low frequency stable trapping mode of the coupled particle-trap system increases as their resonance is tuned to the trap resonance. The strength of the substrate interaction depends on the height of the nanoparticle above the substrate. As a result, a difference in back action mechanism arises for nanoparticle displacements perpendicular to the substrate and along it. For nanoparticle displacements perpendicular to the substrate, the self induced back action component of the trap force arises due to changing interaction with the substrate as well as the trap. On the other hand, for displacements along the substrate, it arises solely due to the changing interaction with the trap. This additional contribution of the substrate leads to more pronounced back action. Numerical simulation results are presented to illustrate these effects using a bowtie engraving as the near-field trap and a nanorod as the trapped plasmonic nanoparticle. The substrate's role may be important in manipulation of plasmonic nanoparticles between successive traps of on-chip optical conveyor belts, because they have to traverse over regions of bare substrate while being handed off between these traps.

variable-area resonator with the hot and ambient heat-exchangers (HHX, AHX) and the regenerator (REG) located at one end enclosed in a coaxial annular tube. Heat-transfer in the heat-exchangers is modeled via source terms which drive the local gas temperature towards the imposed temperature. Turning on the sources terms generates a finite-amplitude perturbation that is amplified until a limit cycle is reached. Simulations have been carried out for HHX temperatures in the range 460K ‐ 500K and an AHX temperature of 300K. Acoustic nonlinearities are detectable from the early stages of operation in the form of streaming. Complex system-wide streaming flow patterns rapidly develop and control the operation of the device in the nonlinear stages. A solution decomposition based on sharp-spectral filtering is adopted to extract the wave-induced Reynolds stresses and energy fluxes at the limit cycle. The key processes involved are traveling-wave streaming in the feedback inertance, periodic vortex roll-up around the edges of the annular tube and near-wall acoustic shear-stresses in the variable-area sections of the resonator. The first drives the mean advection of hot fluid away from the HX/REG (Gedeon streaming), causing heat leakage. The latter is contained by introducing an AHX2 (creating a thermal buffer tube, or TBT) resulting in the saturation of acoustic energy growth in the system. A simplified numerical model is adopted todirectly simulate acoustic streaming as an axially symmetric incompressible flow driven by the acoustic wave-induced stresses. Key features such as the intensity of Gedeon streaming are correctly predicted. The evaluation of the nonlinear energy fluxes reveals that the efficiency of the device deteriorates with the drive ratio and that the acoustic power in the TBT is balanced primarily by the mean advection and thermoacoustic heat transport. Thermoacoustic Stirling heat engines (TASHE) are devices that can convert heat into acoustic power with very high efficiencies. This potential is due to the absence of moving parts and relative simplicity of the components. This results in low manufacturing and maintenance costs making these systems an attractive alternative for clean and effective energy generation. The core energy conversion process occurs in the regenerator ‐ a porous metallic block, placed between a hot and a cold heat-exchanger, sustaining a mean temperature gradient in the axial direction. Acoustic waves propagating through it (with the right phase) can be amplified via a thermodynamic process resembling a Stirling cycle. Most designs explored up to the mid 1980’s were based on acoustic standing waves and had efficiencies typically less than 5%. A significant breakthrough was made by Ceperley (1979) 5 who showed that traveling-waves can extract acoustic energy more efficiently, leading to the concept of traveling-wave TASHE, currently used today 2 . In this configuration the generated acoustic power is in part resupplied to the regenerator via some form of feedback loop and in part directed towards a resonator for energy extraction. This design is the focus of the present study. Improving the technology behind TASHEs is still of particular interest in the last decade with research efforts being made worldwide (see Garrett (2004) 6 for a review). A recent breakthrough, for example, has been made by Tijiani and co-workers 16 who designed a traveling-wave TASHE achieving a remarkable overall efficiency equal to 49% of the Carnot limit. Current design choices for TASHEs, however, are not informed by an accurate description of the underlying fluid mechanics. In particular state-of-the-art prediction capabilities and technological design can significantly benefit from a direct modeling of the nonlinear, system-wide, three-dimensional processes limiting the efficiencies of such devices.

Codoped lithium niobate of congruent and stoichiometric compositions had been successfully grown specifically for holographic data storage applications. The dopants we have selected are Mn and Ce and their role in the recording process is described. Growth methods, sample preparation, doping level measurements, holographic recording data as well as the results of optical characterization and photorefractive properties of the two-photon sensitivity are discussed. Compared to the previously grown crystals, the codoped LiNbO 3 shows a higher sensitivity and dynamic range for recording in red ( λ=632 nm ).

Lead barium niobate (Pb1−xBaxNb2O6) is a very promising material for photorefractive applications in that it has a high ferroelectric-to-paraelectric transition temperature (300–500 °C depending on composition) and simultaneously can have large electro-optic coefficients, because of the nearly vertical morphotropic phase boundary (MPB) near 1−x=0.63. Pb1−xBaxNb2O6 crystals have been grown by the vertical Bridgman method for near-MPB compositions (0.5

Lead barium niobate crystals (Pb1−xBaxNb2O6) are attractive photorefractive materials for holographic data storage. The electro-optic coefficients r33 and r13 are determined using a Mach–Zehnder interferometer setup, and are measured to be 160±20 and 32±4 pm/V, respectively. The angular dependence of the photorefractive two-beam coupling gain is also investigated, and the products of the electro-optic coefficients and the electron-hole competition factor rζ are determined and compared with the electro-optic coefficients obtained using the interferometric method. It is found that the electron-hole competition factor is at least 0.7, indicating that the photorefractive process is mostly due to electrons. The effective trap densities at several wavelengths are also determined from the gain dispersion measurements, and are found to be 1.3–2.2×1016 cm−3.

We develop a plasmonic trapping and conveyor system based on resonant C-shaped engravings driven by polarization rotation and wavelength switching.

We develop a near-field based optical trapping and conveyor belt system based on a novel plasmonic structure: C-shaped engraving. Using polarization rotation and wavelength switching, we demonstrate controlled transport of nanoparticles along different paths.

X-ray differential phase contrast imaging system with a grating-less X-ray source and grating-less detectors are effective for applications with higher X-ray photon energy by decoupling a trade-off the parameters, signal contrast and field-of-view.

New multicomponent InF 3 -based bulk glasses have been investigated. The molar composition of the base glass is 28% InF 3 –20% ZnF 2 –16.5% BaF 2 –12% GaF 3 –9% PbF 2 –6% NaCl–5% SrF 2 –3% CaF 2 –0.5% PrF 3 . A number of variations of the base glass were prepared and their refractive indices and densities measured. Resistance to crystallization allowed the preparation of large pieces of the base glass. The infrared and Raman spectra show that the base composition has a longer wavelength multiphonon edge at 10 μm and a phonon energy of 509 cm −1 , in comparison with 8 μm and 574 cm −1 for ZBLAN, which reveals that the present glasses have a lower phonon energy and a greater transparency in the infrared than ZBLAN. Reduction of PbF 2 concentration in the base composition provided glasses with smaller refractive indices than the base glass.

A transient, two-dimensional drift-diffusion model is developed for optically addressed spatial light modulators made with quantum-well materials. The transport of free and well-confined carriers is considered along with nonlinear transport effects such as velocity saturation, field-dependent carrier escape from quantum wells, and resonant absorption. In addition to full numerical solutions to the transport equations, analytical and simplified numerical solutions are developed to describe basic screening behavior and to give estimates of speed and resolution performance. In particular, a self-consistent small signal model is developed to justify the surface-charge picture often used to describe device operation. This model is also used to simulate grating formation and decay. It is found that the maximum screening rate and peak grating amplitude are achieved using vertical drift lengths much longer than the device length. A detailed analysis of resolution performance is also given in which the effects of ...

A three-color, solid-state, volumetric display based on two-step, two-frequency upconversion in rare earth-doped heavy metal fluoride glass is described. The device uses infrared laser beams that intersect inside a transparent volume of active optical material to address red, green, and blue voxels by sequential two-step resonant absorption. Three-dimensional wire-frame images, surface areas, and solids are drawn by scanning the point of intersection of the lasers around inside of the material. The prototype device is driven with laser diodes, uses conventional focusing optics and mechanical scanners, and is bright enough to be seen in ambient room lighting conditions. QuickTime movie of the three-dimensional display.

We designed, fabricated, and characterized single C-shaped apertures in an Au film, resonant in the visible regime. Our C-shaped apertures showed transmission enhancement of 13–22 times over a square aperture of the same area and suggest as high as 106 enhancement over square apertures that are designed to produce the same near-field spot size. Spectra from individual apertures demonstrate the ability to tune this resonance over 70nm by scaling the dimensions of the apertures. This shows the C aperture to be a versatile tool for gaining high-resolution, enhanced transmission through single subwavelength apertures at optical wavelengths.

We report abnormally large positive and negative lateral optical beam shifts at a metal–air interface when the surface plasmon resonance of the metal is excited. The optimal thickness for minimal resonant reflection is identified as the critical thickness above which a negative beam displacement is observed. Experimental results show good agreement with theoretical predictions and the large observed bidirectional beam displacements also indicate the existence of forward and backward surface propagating waves at the surface plasmon resonance of the metal.

A zoom objective lens for a multi-layer optical rec ording has been designed. A newly proposed optical power arrangement enables varying back focal length while focal length invariant by a linear movement of sin gle zooming component. The zoom lens is implemented into multi- layer and multi-bit holographic recording system em ploying 405 nm blue lasers. 1. INTRODUCTION Recently, multilayer micro holographic optical disc systems have been investigated to attain high capa city and high data transfer rate [1,2]. In the multilayer recordi ng, micro-holograms are recorded throughout the vol ume of recording material by changing the recording depth. For such multilayer recording systems, objective l ens accesses to multiple recording layers. The design of objecti ve lens needs to satisfy couple of constraints. Fir st, working distance, air spacing between objective lens and re cording disc, is unchanged while changing the recor ding layer. Numerical aperture (NA) must be an invariant for th e range of recording depth to equalize transverse s ize and modulation of index of refraction of the micro holo grams. Ideally, the number of moving elements shoul d be a minimum. Also, a linear relation between zooming of the element and recording depth is preferable. Typical way to design such optics is depicted in Fi g. 1. First, an intermediate image, a virtual or re al one, is formed by a movable zooming optics. Then, the inter mediate image is relayed to a final focal point ins ide a recording medium by a secondary optics consisting o f high NA objective elements. Moving the first opti cs along optical axis alters conjugate ratio between the int ermediate image and final image, therefore, the fin al image position also moves, which ends up with selection of writing depth. The approach is rather a simple one however we immediately notice several drawbacks of the approac h if we recall the design requirement for optical d ata storage applications. First, the system focal length varies as the writing depth changes. Consequently, NA va ries as selection of recording layers. As a result, a varia ble aperture and tuning of laser power is needed to equalize the transverse size and modulation of index of refracti on of the micro holograms. Second, the location of the final image nonlinearly moves with respect to the movement of t he zooming element. This would impose an additional requirement on actuators for selection of writing d epth. To overcome such issues, we propose an optica l power arrangement having constant focal length as well as linear movement of zooming element. Note that, eve n being able to implement such additional features, the pro posed optical power arrangement requires only one m oving component. Thus, our approach inherits the simple i mplementation of the conventional approach. Importa ntly, such a minimum optical power arrangement is possible onl y if specific combination of power is adopted for t he zooming optical component. In this paper, first analysis of the proposed power arrangement is described. Based on the power arrangement, we discuss design of all off-the-shelf write/read optics having a constant numerical aper ture (NA) of 0.4 for a range of writing depth of 0.2 mm. Design and implementation of multi-layer and multi-bit mic ro holographic recording system employing blue lasers will be addressed.

Plasmonic Near-Field Transducers (NFTs) find use in Energy-Assisted Magnetic Recording (EAMR) schemes, where a high-anisotropy recording medium is locally heated to the Curie temperature, allowing conventional magnetic recording heads to overcome the high coercivity of the medium. However, coupling efficiency is low, and the conditions for excitation and resonance are poorly understood. In this work, we explore the behavior of a canonical EAMR setup including rectangular dielectric waveguide, elliptic cylinder gold NFT, and conductive planar recording medium. We systematically examine the effects of polarization and angle; spacing between NFT, waveguide, and recording medium; and variations in NFT size and incident wavelength.

A multiple page fully digital holographic data storage system is demonstrated. This system is used to store and retrieve digital image and compressed video data with a photorefractive crystal. Architecture issues related to spatio-rotational multiplexing and novel error-correcting encoding techniques used to achieve low bit-error rates are discussed.

Today, computational fluid dynamics (CFD) research is almost impossible without computer-generated visualizations of the very large amounts of data resulting from numerical simulations. Although good techniques now exist for analysis of scalar data, most existing techniques for the visualization of vector fields-the predominant data type in CFD-meet only part of what is required. Common techniques such as arrow plots, streamlines, and particles work well for 2D applications, but for 3D data sets they often lead to cluttered displays. For tensors, which are much more complex and abstract entities the problem is even more severe. There is a real need for visualization, but there are no simple solutions. Many researchers have recognized this challenge and developed new techniques. We restrict ourselves to open research issues. We proceed in three ways. First, we propose a classification of existing vector and tensor field visualization techniques based on work by Delmarcelle and Hesselink (1994) and point out research gaps in this classification scheme. Second, we discuss feature-based visualization, which shows higher level descriptions derived from elementary data. Third, we consider the role of visualization in the research process, again revealing gaps in our current know-how concerning visualization of vector and tensor fields. >