We have investigated the feasibility of significantly improving the performance of currently favored uncooled
infrared (IR) detectors based on Si or VOx microbolometers with a new design employing freestanding suspended
network of single-walled carbon nanotubes (SWCNTs). Such networks have high absorption coefficient, high
temperature coefficient of the resistance (TCR) and extremely low thermal mass. This combination of parameters
translates into an uncooled IR detector with high sensitivity and a very fast temporal response. We show estimates
of key parameters for such a device, demonstrate a method to prepare it using suspended SWCNT networks
achieved by selective removal of a sacrificial oxide layer, thereby forming a cavity under the SWCNT network. We
also present TCR and photothermal bolometric response data of this conceptual structure.
The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale lithography for microelectromechanical systems (MEMS) applications is also shown. A substrate to ChG/silver thickness etching ratio of ~10 is obtained for the transfer of patterns into silicon using reactive ion etching (RIE), more than a fivefold increase compared to traditional polymer photoresist.
The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are
demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale
patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent
ChG patterns can be useful as such on the surface, or be used to transfer the etched pattern into silicon or other
substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater
transfer ratio than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with
inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR
region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale
lithography for MEMS applications is also shown. The process consists of the following steps: ChG film deposition, Ag
film deposition, irradiation through a grayscale mask, removal of the excess Ag and the transfer of the pattern to Si by
dry etching. A substrate to ChG thickness etching ratio of ~ 10 is obtained for the transfer of patterns into silicon, more
than a five fold increase compared to traditional polymer photoresist.
Thin film multi-layered chalcogenide glass waveguide structures have been fabricated for evanescent wave sensing of bio toxins and other applications. Thin films of Ge containing chalcogenides have been deposited onto Si substrates, with a-GeSe2 as the cladding layer and a-GeSbSe as the core layer to form the slab waveguide. Channel waveguides have been written in the slab waveguides by appropriate light the through a mask. The photo-induced structural changes in the core layer selectively enhance refractive index at the portions of interest and thus confining the light to the channels. The waveguides have been characterized and tested for the guiding of light.
We have systematically designed, fabricated, and tested chalcogenide-glass waveguides. Among all the characterization techniques, we have found that the prism-coupling method is the most effective and accurate for determining all the parameters describing the performance of the slab waveguides. Furthermore, we have also achieved the end-fire coupling in these waveguides to study the characteristics of the transmitted beams. These waveguides can be optimized eventually for the biosensor applications.
There is strong need for low cost, optically active materials whose high electro-optic (EO) and second harmonic generation (SHG) properties can be engineered flexibly, in bulk and fiber forms. Therefore, we have fabricated transparent ferroelectric composites consisting of strontium barium niobate crystallites in a refractive index compatible tellurium oxide (TeO2) glass matrix. Several glass compositions, in the series x SrO-(10-x) BaO-y (Nb2O5)-(90-y) TeO2 (where x=2.5, 5 and 7.5 and y = 10, 15, 20 and 25), have been prepared by a conventional melt quenching technique. The compositions have been selected on the basis of thermal stability data obtained from differential thermal analysis (DTA). X-ray diffraction studies indicate ferroelectric phase formation in the controlled crystallized glasses. The non-centrosymmetric nature of the crystallized regions has been monitored via observing the second harmonic signal.
Although the success of demonstrating tellurite glass as a waveguide material in many applications, including tellurite fiberization, Nd3+-doped tellurite fiber laser, and 1.5 μm ultra-broad band Er3+-doped optical amplifier, the advance of tellurite is still necessary in the areas of improving the quality of waveguide and understanding the correlations among processing, structure, and desired property, such as nonlinearity, rare-earth spectroscopy, nanocrystalline doping, and microstructured holey fiber. In the paper, we report some initial experimental results on fiberization processing of KNbO3-Na2O-ZnO-TeO2 and Er2O3-WO3-TeO2 systems. The report, in particular, focuses on the thermal characteristics of these glasses.
Numerous studies have shown that the orientational decay rate of nonlinear optical (NLO) polymers increases as the glass transition temperature is approached. A high glass transition temperature is thus beneficial to long-term poling stability. Here we report on the synthesis and nonlinear optical properties of poly(N-MNA Acrylamide), which as a glass transition temperature of 205 degree(s)C. This side-chain polymer has the NLO organic molecule 2- methyl-4-nitroaniline (MNA) attached through a carbonyl group to an acrylic polymer backbone. Second harmonic Maker fringe measurements used to evaluate the second-order optical nonlinearity in corona-poled thin films resulted in a second harmonic coefficient d33 approximately equals 3 pm/V at 1064 nm. Thin films were quite transparent with an absorption maximum for poled samples occurring near approximately 320 nm.
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