Publications

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We design and fabricate arrays of diffractive optical elements (DOEs) to realize neutral atom micro-traps for quantum computing. We initialize a single atom at each site of an array of optical tweezer traps for a customized spatial configuration. Each optical trapping volume is tailored to ensure only one or zero trapped atoms. Specifically designed DOEs can define an arbitrary optical trap array for initialization and improve collection efficiency in readout by introducing high-numerical aperture, low-profile optical elements into the vacuum environment. We will discuss design and fabrication details of ultra-fast collection DOEs integrated monolithically and coaxially with tailored DOEs that establish an optical array of micro-traps through far-field propagation. DOEs, as mode converters, modify the lateral field at the front focal plane of an optical assembly and transform it to the desired field pattern at the back focal plane of the optical assembly. We manipulate the light employing coherent or incoherent addition with judicious placement of phase and amplitude at the lens plane. This is realized through a series of patterning, etching, and depositing material on the lens substrate. The trap diameter, when this far-field propagation approach is employed, goes as 2.44λF/#, where the F/# is the focal length divided by the diameter of the lens aperture. The 8-level collection lens elements in this presentation are, to our knowledge, the fastest diffractive elements realized; ranging from F/1 down to F/0.025. © 2012 SPIE.

Through this effort, Sandia and Lockheed Martin Aeronautics Company (LM Aero) sought to assess the feasibility of (1) applying special materials to a defense application; (2) developing a piezoelectric-based micro thermophotovoltaic (TPV) cell; and (3) building and delivering a prototype laboratory emission measurement system. This project supported the Stockpile Research & Development Program by contributing to the development of radio frequency (RF) MEMS- and optical MEMS-based components - such as switches, phase shifters, oscillators, and filters - with improved performance and reduced weight and size. Investigation of failure mechanisms and solutions helped to ensure that MEMS-based technology will meet performance requirements and long term reliability goals in the specified environments dictated by Lockheed Martin's commercial and defense applications. The objectives of this project were to (1) fabricate and test materials for military applications; (2) perform a feasibility study of a piezoelectric-based micro TPV cell; and (3) build and deliver a prototype laboratory emission measurement system. Sandia fabricated and tested properties of materials, studied options for manufacturing scale-up, and delivered a prototype IR Emissometer. LM Aero provided material requirements and designs. Both participated in the investigation of attachment methods and environmental effects on material performance, a feasibility study of piezoelectric TPV cells, an investigation and development of new approaches to implement the required material functionality, and analysis and validation of material performance physics, numerical models, and experimental metrology.

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In this work, we describe the most recent progress towards the device modeling, fabrication, testing and system integration of active resonant subwavelength grating (RSG) devices. Passive RSG devices have been a subject of interest in subwavelength-structured surfaces (SWS) in recent years due to their narrow spectral response and high quality filtering performance. Modulating the bias voltage of interdigitated metal electrodes over an electrooptic thin film material enables the RSG components to act as actively tunable high-speed optical filters. The filter characteristics of the device can be engineered using the geometry of the device grating and underlying materials. Using electron beam lithography and specialized etch techniques, we have fabricated interdigitated metal electrodes on an insulating layer and BaTiO3 thin film on sapphire substrate. With bias voltages of up to 100V, spectral red shifts of several nanometers are measured, as well as significant changes in the reflected and transmitted signal intensities around the 1.55um wavelength. Due to their small size and lack of moving parts, these devices are attractive for high speed spectral sensing applications. We will discuss the most recent device testing results as well as comment on the system integration aspects of this project. © 2010 Copyright SPIE - The International Society for Optical Engineering.

The authors have developed two versions of a flexible fabrication technique known as membrane projection lithography that can produce nearly arbitrary patterns in '212 D' and fully three-dimensional (3D) structures. The authors have applied this new technique to the fabrication of split ring resonator-based metamaterials in the midinfrared. The technique utilizes electron beam lithography for resolution, pattern design flexibility, and alignment. The resulting structures are nearly three orders of magnitude smaller than equivalent microwave structures that were first used to demonstrate a negative index material. The fully 3D structures are highly isotropic and exhibit both electrically and magnetically excited resonances for incident transverse electromagnetic waves.

3-D cubic unit cell arrays containing split ring resonators were fabricated and characterized. The unit cells are {approx}3 orders-of-magnitude smaller than microwave SRR-based metamaterials and exhibit both electrically and magnetically excited resonances for normally incident TEM waves in addition to showing improved isotropic response.

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The combination of Proximity-field nanoPatterning (PnP) and graded temperature ALD has enabled the synthesis of robust three dimensional nanostructures. The PnP process uses a simple elastomeric optical phase mask to generate a complex three dimensional interference pattern in photopolymer 1. Once the photopolymer structure has been obtained, it is subsequently used as a template for graded temperature ALD. The graded temperature ALD chemistry is used to coat and lock-in the designed nanostructure without melting the template. This process generates a thermally robust nanostructure for further, higher temperature, ALD surface treatments. The ALD chemistry is performed at various (increasing) temperatures to secure the nanostructure and to reduce the macroscopic stress of the structure as higher temperature depositions are performed. Three methods for nanostructure characterization have been useful in interrogating these structures: quartz crystal microbalance (QCM), optical interference, and focused ion beam scanning electron microscopy (FIB-SEM). This paper will cover the fabrication process for generating PnP nanostructures. Details of the graded temperature ALD chemical process for AI2O3 will be covered. Also, structural characterizations using SEM and optical interference will be used to quantify the degree of deposition and the thermal stability of these interesting structures. © The Electrochemical Society.

We have developed a system to measure the directional thermal emission from a surface, and in turn, calculate its emissivity. This approach avoids inaccuracies sometimes encountered with the traditional method for calculating emissivity, which relies upon subtracting the measured total reflectivity and total transmissivity from unity. Typical total reflectivity measurements suffer from an inability to detect backscattered light, and may not be accurate for high angles of incidence. Our design allows us to vary the measurement angle (θ) from near-normal to ∼80°, and can accommodate samples as small as 7 mm on a side by controlling the sample interrogation area. The sample mount is open-backed to eliminate shine-through, can be heated up to 200°C, and is kept under vacuum to avoid oxidizing the sample. A cold shield reduces the background noise and stray signals reflected off the sample. We describe the strengths, weaknesses, trade-offs, and limitations of our system design, data analysis methods, the measurement process, and present the results of our validation of this Variable-Angle Directional Emissometer.

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We present simulations and measurements of a technology that can manipulate thermal angular and wavelength emission. This work is representative of Sandia National Laboratories' efforts to investigate advanced technologies that are not currently accessible for reasons such as risk, cost, or limited availability. The goal of this project is to demonstrate a passive thermal emission management surface that can tailor the direction of emission as well as the wavelength bands of emission. This new proposed technology enables thermal emission pattern management by structuring the surface. This structuring may be in either the lateral or depth dimension. A lateral structuring consists of a shallow grating on a metal surface. This air/metal interface allows photon/plasmon coupling, which has been shown to coherently and preferentially emit at certain wavelengths.

Alternative solutions are desired for mid-wavelength and long-wavelength infrared radiation detection and imaging arrays. We have investigated quantum dot infrared photodetectors (QDIPs) as a possible solution for long-wavelength infrared (8 to 12 {mu}m) radiation sensing. This document provides a summary for work done under the LDRD 'Infrared Detection and Power Generation Using Self-Assembled Quantum Dots'. Under this LDRD, we have developed QDIP sensors and made efforts to improve these devices. While the sensors fabricated show good responsivity at 80 K, their detectivity is limited by high noise current. Following efforts concentrated on how to reduce or eliminate this problem, but with no clear path was identified to the desired performance improvements.

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The LIGA microfabrication technique offers a unique method for fabricating 3-dimensional photonic lattices based on the Iowa State "logpile" structure. These structures represent the [111] orientation of the [100] logpile structures previously demonstrated by Sandia National Laboratories, The novelty to this approach is the single step process that does not require any alignment. The mask and substrate are fixed to one another and exposed twice from different angles using a synchrotron light source. The first exposure patterns the resist at an angle of 45 degrees normal to the substrate with a rotation of 8 degrees. The second exposure requires a 180 degree rotation about the normal of the mask and substrate. The resulting pattern is a vertically oriented logpile pattern that is rotated slightly off axis. The exposed PMMA is developed in a single step to produce an inverse lattice structure. This mold is filled with electroplated gold and stripped away to create a usable gold photonic crystal. Tilted logpiles demonstrate band characteristics very similar to those observed from [100] logpiles. Reflectivity tests show a band edge around 5 μm and compare well with numerical simulations.

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