Stanley K H Pau

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Chapters

• Balakrishnan, K., & Pau, S. K. (2015). Self-assembled organic optical materials. In McGraw-Hill Encyclopedia of Science and Technology.

Journals/Publications

• Koch, T. L., Norwood, R. A., Pau, S., Kim, K., Frish, J., Nishant, A., Jiang, L., Kleine, T. S., Brusberg, L., Himmelhuber, R., & Pyun, J. (2022). SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics. Journal of Lightwave Technology, 40(12), 3839-3844. doi:10.1109/jlt.2022.3149872
• Norwood, R. A., Koch, T. L., Pau, S., Nishant, A., Kleine, T. S., Frish, J. I., Himmelhuber, R., Showghi, S., Kim, K., Jiang, L., Martin, K. P., Brusberg, L., & Pyun, J. (2022). Rapid photolithographic fabrication of high density optical interconnects using refractive index contrast polymers. Optical Materials Express, 12(5), 1932. doi:10.1364/ome.454195
• Pau, S. K. (2022). Birefringent coating to remove polarization dependent phase shift. Opt. Express, 30(12), 20629-20646. doi:https://doi.org/10.1364/OE.458859
• Pau, S. K. (2022). Generalized elliptical retarder design and construction using nematic and cholesteric phase liquid crystal polymers. Opt. Express, 30(10), 16734-16747. doi:https://doi.org/10.1364/OE.456874
• Pau, S. K. (2022). Patterned achromatic elliptical polarizer for short wave infrared imaging polarimetry. Opt. Express, 30(2), 1249-1260. doi:https://doi.org/10.1364/OE.445253
• Pau, S. K. (2022). Rapid photolithographic fabrication of high density optical interconnects using refractive index contrast polymers. Opt. Mater. Express, 12(5), 1932-1944. doi:https://doi.org/10.1364/OME.454195
• Pau, S. K. (2022). Smartprint single-mode flexible polymer optical interconnect for high density integrated photonics. J. Light. Technol., 40(12), 3839-3844. doi:10.1109/JLT.2022.3149872
• Pau, S., Miller, S., & Jiang, L. (2022). Birefringent coating to remove polarization aberrations. Optics Express, 30(12), 20629. doi:10.1364/oe.458859
• Pau, S., Miller, S., & Jiang, L. (2022). Generalized elliptical retarder design and construction using nematic and cholesteric phase liquid crystal polymers. Optics Express, 30(10), 16734. doi:10.1364/oe.456874
• Pau, S. K. (2021). Low-loss adiabatic silicon nitride to polymer waveguide coupler with relaxed tolerance for high port density interconnects. Photonics Technology Letters, 33(22), 1227-1230.
• Pau, S. K. (2021). Patterned liquid crystal polymer C-plate retarder and color polarizer. Applied Optics, 60(6), 1500-1507.
• Pau, S., Jiang, L., Miller, S., & Tu, X. (2021). Patterned liquid crystal polymer C-plate retarder and color polarizer. Applied Optics, 60(6), 1500. doi:10.1364/ao.416845
• Pau, S. K. (2020). Color full Stokes polarization fringe projection 3D imaging. Optics and Lasers in Engineering, 130, 106088. doi:https://doi.org/10.1016/j.optlaseng.2020.106088
• Pau, S. K. (2020). Division of focal plane RGB full-Stokes imaging polarimeter. Applied Optics, 59(22), G33. doi:https://doi.org/10.1364/AO.391027
• Pau, S. K. (2020). Microfabrication of color filter array utilizing color dye SU-8 photoresists. Applied Optics, 22, G137. doi:https://doi.org/10.1364/AO.391579
• Pau, S. K. (2020). Observation of elliptically polarized light from total internal reflection in bubbles. Scientific Reports, 10, 8725. doi:https://doi.org/10.1038/s41598-020-65410-5
• Ding, Y., & Pau, S. (2019). Circularly and elliptically polarized light under water and the Umov effect. LIGHT-SCIENCE & APPLICATIONS, 8.
• Ding, Y., Bushroe, F., Pau, S. K., & Gauvin, M. (2019). Innovative software simulation techniques to design specular curved baffle designs in ground- and space-based telescopes. Proc. SPIE, 11103(111030J), 14. doi:https://doi.org/10.1117/12.2535754
• Miller, S., Tu, X., Wang, L., & Pau, S. (2019). Polarizing beam splitter cube for circularly and elliptically polarized light. OPTICS EXPRESS, 27(11), 16258-16270.
• Tian, X., Tu, X., Della, C. K., Yao, G., Cai, H., Brock, N., Pau, S., & Liang, R. (2019). Multi-wavelength quantitative polarization and phase microscope. BIOMEDICAL OPTICS EXPRESS, 10(4), 1638-1648.
• Ding, Y., Kerviche, R., Ashok, A., & Pau, S. (2018). Eavesdropping of display devices by measurement of polarized reflected light. APPLIED OPTICS, 57(19), 5483-5491.
• Tian, X., Tu, X., Zhang, J., Spires, O., Brock, N., Pau, S., & Liang, R. (2018). Snapshot multi-wavelength interference microscope. OPTICS EXPRESS, 26(14), 18279-18291.
• Tu, X., Spires, O. J., Tian, X., Brock, N., Liang, R., & Pau, S. (2018). Division of amplitude RGB full-Stokes camera using micro-polarizer arrays (vol 25, pg 33160, 2017). OPTICS EXPRESS, 26(4), 4192-4193.
• Ding, Y., Ashok, A., & Pau, S. (2017). Real-time robust direct and indirect photon separation with polarization imaging. OPTICS EXPRESS, 25(23), 29432-29453.
• Tu, X., Jiang, L., Ibn-Elhaj, M., & Pau, S. (2017). Design, fabrication and testing of achromatic elliptical polarizer. OPTICS EXPRESS, 25(9), 10355-10367.
• Tu, X., Spires, O. J., Tian, X., Brock, N., Liang, R., & Pau, S. K. (2017). Division of amplitude RGB full-Stokes camera using micro-polarizer arrays. OPTICS EXPRESS, 25(26), 33160. doi:https://doi.org/10.1364/OE.25.033160
• Tu, X., & Pau, S. (2016). Optimized design of N optical filters for color and polarization imaging. OPTICS EXPRESS, 24(3), 3011-3024.
• Hsu, W., Davis, J., Balakrishnan, K., Ibn-Elhaj, M., Kroto, S., Brock, N., & Pau, S. (2015). Polarization microscope using a near infrared full-Stokes imaging polarimeter. OPTICS EXPRESS, 23(4), 4357-4368.
• Hsu, W., Davis, J., Chipman, R., & Pau, S. (2015). Compound dichroic polarizers with wavelength-dependent transmission axes. APPLIED OPTICS, 54(21), 6476-6481.
• Balakrishnan, K., Hsu, W., Mataka, S., & Pau, S. (2014). Tunable light emission from co-assembled structures of benzothiadiazole molecules. Chemical communications (Cambridge, England), 50(42), 5600-3.
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  Co-assembled structures possessing tunable light emission from 510-690 nm have been prepared using various compositions of two different 4,7-substituted benzothiadiazole molecules, 1 and 2. The preferential incorporation and co-localization of 1 and 2 to produce co-assemblies are possible because of structural similarities and allow for tuning of morphology and light emission.
• Hsu, W., Balakrishnan, K., Ibn-Elhaj, M., & Pau, S. (2014). Infrared liquid crystal polymer micropolarizer. Applied optics, 53(23), 5252-8.
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  The ability to create arbitrary patterned linear and circular infrared (IR) liquid crystal polymer (LCP) polarizers is demonstrated. The operating wavelength of the thin-film polarizer ranges from 700 to 4200 nm. The linear micropolarizer is fabricated using IR dichroic dye as a guest in LCP host with feature size as small as 4 μm. The circular micropolarizer is fabricated using cholesteric LCPs with feature size as small as 6.2 μm.
• Hsu, W., Myhre, G., Balakrishnan, K., Brock, N., Ibn-Elhaj, M., & Pau, S. (2014). Full-Stokes imaging polarimeter using an array of elliptical polarizer. OPTICS EXPRESS, 22(3), 3063-3074.
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  In this paper, a full-Stokes imaging polarimeter operating at 580 nm using an array of elliptical polarizers is presented. The division-of-focal-plane polarimeter utilizes a set of four optimized measurements which represent a regular tetrahedron inscribed in the Poincare sphere. Results from the device fabrication, instrument calibration and characterization are presented. The performance of the optimized full Stokes polarimeter, as defined by size of the standard deviation of the degree of circular polarization, is found to be approximately five times better than the performance of the simple full-Stokes polarimeter. (C) 2014 Optical Society of America
• Pau, S., Balakrishnan, K., Hsu, W., & Mataka, S. (2014). Tunable light emission from co-assembled structures of benzothiadiazole molecules. Chem. Commun., 50(42), 5600-5603. doi:10.1039/c4cc01685h
• Hsu, W., & Pau, S. (2013). Image formation of a one dimensional polynomial mirror: Numbers and parities of images. Optics and Lasers in Engineering, 51(8), 986-993.
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  Abstract: This paper addresses the image formation, including both real images and virtual images, of the polynomial mirrors when analyzed by using ray optics. The imaging properties of polynomial mirrors, including mirrors with quadratic, cubic, and quartic polynomial shapes, are reviewed and generalized to higher order polynomial mirrors by being approximated as a piecewise set of displaced parabolic mirrors. The conditions in which multiple virtual images can be formed and the parities of the virtual images are investigated both theoretically and experimentally. © 2013 Elsevier Ltd. All rights reserved.
• Hsu, W., Johnson, S., & Pau, S. (2013). Multiplex localization imaging and sub-diffraction limited measurement. Journal of Modern Optics, 60(5), 414-421.
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  Abstract: A novel technique, multiplex localization imaging, is proposed to enhance the image reconstruction of point sources beyond the diffraction limit for an incoherent remote sensing system. The technique utilizes position localization of point sources to create an image of a scene and to allow sub-diffraction limited measurement. Two types of algorithms, mean calculations and chi-square statistics, are implemented to analyze the limits of position localization. Three different multiplex localization imaging methods, time-, color-, and polarization-multiplexing, were investigated experimentally. The resolution of multiplex localization imaging was found to be 14 times better than the diffraction limit of the optics. The multiplex localization imaging technique has applications in remote sensing and astronomy, such as position measurement, multiple targets tracking, and image enhancement. © 2013 Taylor and Francis Group, LLC.
• Johnson, S., Küppers, F., & Pau, S. (2013). Efficiency of continuous-wave solar pumped semiconductor lasers. Optics and Laser Technology, 47, 194-198.
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  Abstract: We report the results of an efficient solar pumped semiconductor laser system that uses high efficiency multi-junction photovoltaic cells and laser diodes in order to achieve the sunlight to laser light conversion efficiency of over 10 without any active cooling and concentration optics. Semiconductor lasers with wavelength from 445 nm to 1550 nm are powered directly by an array of photovoltaic (PV) cells under one sun illumination (100 mW/cm 2). The maximum energy efficiency reaches 10.34 at 976 nm with an output power of 4.31 W. This system is inherently more efficient than direct solar pumped lasers that have been studied in the past and could play a key role in future renewable energy production and power beaming applications. © 2012 Elsevier Ltd.
• Pau, S., Hsu, W., Ma, J., Myhre, G., Balakrishnan, K., & Pau, S. K. (2013). Patterned cholesteric liquid crystal polymer film. Journal of the Optical Society of America. A, Optics, image science, and vision, 30(2).
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  Herein, the ability to create arbitrarily patterned circular polarized optical devices is demonstrated by using cholesteric liquid crystal polymer. Photoalignment with polarized ultraviolet light is utilized to create aligned cholesteric liquid crystal films. Two different methods, thermal annealing and solvent rinse, are utilized for patterning cholesteric liquid crystal films over large areas. The patterned cholesteric liquid crystal films are measured using a Mueller matrix imaging polarimeter, and the polarization properties, including depolarization index, circular diattenuation (CD), and circular retardance are derived. Patterned nonlinearly polarized optical devices can be fabricated with feature sizes as small as 20 μm with a CD of 0.812±0.015. Circular polarizing filters based on polymer cholesteric liquid crystal films have applications in three-dimensional displays, medical imaging, polarimetry, and interferometry.
• Manakasettharn, S., Hsu, T., Myhre, G., Pau, S., Taylor, J. A., & Krupenkin, T. (2012). Transparent and superhydrophobic Ta₂O₅ nanostructured thin films. Optical Materials Express, 2(2), 214-221.
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  Abstract: Transparent Ta2O5 nanostructured thin films have been fabricated using a multi-step anodization process. Obtained by a combination of the nanostructured surface and the deposition of the hydrophobic CFx coating, the transparent films can be made highly water repellent or superhydrophobic useful for self-cleaning and anti-fogging optical coatings. Contact angle measurements and optical transmittance curves of the nanostructured films are in good agreement with theoretical calculations. © 2012 Optical Society of America.
• Pau, S., Balakrishnan, K., Sayyad, A. S., Myhre, G., Mataka, S., & Pau, S. K. (2012). Multi-mode waveguides from ultra-long self-assembled hexagonal faceted microtubules of a benzothiadiazole molecule. Chemical communications (Cambridge, England), 48(95).
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  Length controlled (μm-mm-cm) self-assembly of hexagonal faceted microtubules has been achieved using a phase-transfer solution processing approach from . The self-assembled structures exhibit both polarized light emission and multi-mode waveguide properties over large length scales. The multi-mode waveguide characteristics are analyzed using a combination of experiment and finite-difference-time-domain calculations.
• Pau, S., Myhre, G., Hsu, W., Peinado, A., LaCasse, C., Brock, N., Chipman, R. A., & Pau, S. K. (2012). Liquid crystal polymer full-stokes division of focal plane polarimeter. Optics express, 20(25).
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  A division-of-focal-plane polarimeter based on a dichroic dye and liquid crystal polymer guest-host system is presented. Two Stokes polarimeters are demonstrated: a linear Stokes and the first ever Full-Stokes division-of-focal-plane polarimeter. The fabrication, packaging, and characterization of the systems are presented. Finally, optimized polarimeter designs are discussed for future works.
• Jiang, L., Whitten, W. B., & Pau, S. (2011). A charged-particle manipulator utilizing a co-axial tube electrodynamic trap with an integrated camera. Journal of Instrumentation, 6(10).
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  Abstract: A charged-particle manipulator was designed and fabricated with an integrated imaging camera allowing real-time in-situ monitoring of trapped particle motion even when the trap device is under motion or rotation. The trap device was made of two co-axial electrically conductive tubes with diameters of 5.5 mm and 7 mm for the inner tube and outer tube, respectively; the imaging camera with its optical fiber bundle was integrated within the tubular trap device to realize a single instrument functioning as a manipulator. Motion of suspended microparticles of 3 μm to 50 μm in diameter can be monitored using the integrated camera regardless of the trap device orientations. This manipulator provides capability of controlled manipulation of trapped particles by tuning the operating conditions while monitoring the feedback of real-time particle motion. Imaging of suspended particles was not interrupted while the manipulator was translated and/or rotated. This integrated manipulator can be used for charged particle transport and repositioning. © 2011 IOP Publishing Ltd and SISSA.
• Jiang, L., Whitten, W. B., & Pau, S. (2011). A planar ion trapping microdevice with integrated waveguides for optical detection. Optics Express, 19(4), 3037-3043.
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  PMID: 21369127;Abstract: A planar ion trap with an integrated waveguide was fabricated and characterized. The microdevice, consisting of a 1 mm-diameter onehole ring trap and multi-mode optical waveguides, was made on a glass wafer using microfabrication techniques. The experimental results demonstrate that the microdevice can trap 1.5 μm-to 150 μm-diameter charged particles in air under an alternating electric field with the amplitude and frequency varying from 100 V to 750 V, and 100 Hz to 700 Hz, respectively. The on-chip waveguide is capable of detecting the presence of a particle in the trap, and the particle secular motion frequency was found to depend on the input alternating signal amplitude and frequency. © 2011 Optical Society of America.
• Johnson, S., Pau, S., & Küppers, F. (2011). All-optical re-timing using the "soliton molecule effect". AIP Conference Proceedings, 1389, 701-704.
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  Abstract: We show how a stable bound soliton pair (or "soliton molecule") maintains an equilibrium temporal separation during its propagation along a dispersion alternating fiber. Experimental results of a scheme utilizing this soliton molecule action to re-time a return-to-zero on-off-keyed (RZ-OOK) data stream at 10.7 Gbit/s are presented. © 2011 American Institute of Physics.
• Johnson, S., Pau, S., & Küppers, F. (2011). Experimental demonstration of optical retiming using temporal soliton molecules. Journal of Lightwave Technology, 29(23), 3493-3499.
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  Abstract: We experimentally demonstrate optical retiming of a 10.7 Gb/s data stream utilizing the property of bound soliton pairs (or soliton molecules) to relax to an equilibrium temporal separation after propagation through a nonlinear dispersion alternating fiber span. Pulses offset up to 16 ps from bit center are successfully retimed. The results of the experiment are in agreement with numerical simulations. An enhanced version of this retiming scheme is analyzed using numerical simulations. © 2011 IEEE.
• Kuwahara, S. S., Cuello, J. L., Myhre, G., & Pau, S. (2011). Growth of the green algae Chlamydomonas reinhardtii under red and blue lasers. Optics and Lasers in Engineering, 49(3), 434-438.
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  Abstract: Red and blue lasers, holding promise as an electric light source for photosynthetic systems on account of being true monochromatic, high-power, and having high electrical-conversion efficiency, were employed in growing a green alga, Chlamydomonas reinhardtii. The laser treatments tested included: 655-nm Red; 680-nm Red; 655-nm Red474-nm Blue and 680-nm Red474-nm Blue. A white cold cathode lamp with spectral output similar to that of white fluorescent lamp served as control. C. reinhardtii successfully grew and divided under the 655 and 680-nm red lasers as well as under the white-light control. Supplementing either red with blue laser, however, resulted in increased algae cell count that significantly exceeded those under both red lasers and the white-light control on average by 241%.
• Llull, P., Myhre, G., & Pau, S. (2011). Lens array Stokes imaging polarimeter. Measurement Science and Technology, 22(6).
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  Abstract: We have successfully constructed and tested two portable multi-lens polarization cameras whose designs differ in the ability to measure circularly polarized light. The cameras operate by acquiring multiple images of a scene at different polarizations using multiple lenses. An algorithm is used to align and combine the images, correcting for exposure and lens variation, to generate accurate Stokes images. Comparisons are made between four- and eight-lens Stokes imaging cameras. The multi-lens camera and software error corrections can be implemented at a relatively low cost. © 2011 IOP Publishing Ltd.
• Myhre, G., Sayyad, A., & Pau, S. (2011). Bio-inspired structural color waveplates and polarizers and their applications. Optics InfoBase Conference Papers.
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  Abstract: By studying the polarization property of jeweled beetles, we develop novel optical coatings that can be patterned at high spatial resolution and have precise optical retardance and polarization dependent absorption. © 2011 OSA.
• Myhre, G., Sayyad, A., Mataka, S., & Pau, S. (2011). Patterned polarized fluorescence from a thin film. Applied Physics Letters, 99(9).
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  Abstract: Patterned polarized fluorescence from a thin film comprised of fluorescent dichroic dye dispersed in liquid crystalline polymer is demonstrated with features as small as 11 m. Cooperative alignment of these fluorescent dichroic molecules in a liquid crystal polymer leads to films exhibiting polarized green, red, and yellow emission. The dichroic fluorescence emission ratios for these films are 10 to 16 depending on the type of the dye. This simple strategy could be utilized for generating large area linearly polarized light sources or electroluminescent displays. © 2011 American Institute of Physics.
• Pau, S., Jiang, L., Whitten, W. B., & Pau, S. K. (2011). A planar ion trapping microdevice with integrated waveguides for optical detection. Optics express, 19(4).
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  A planar ion trap with an integrated waveguide was fabricated and characterized. The microdevice, consisting of a 1 mm-diameter one-hole ring trap and multi-mode optical waveguides, was made on a glass wafer using microfabrication techniques. The experimental results demonstrate that the microdevice can trap 1.5 μm- to 150 μm-diameter charged particles in air under an alternating electric field with the amplitude and frequency varying from 100 V to 750 V, and 100 Hz to 700 Hz, respectively. The on-chip waveguide is capable of detecting the presence of a particle in the trap, and the particle secular motion frequency was found to depend on the input alternating signal amplitude and frequency.
• Pau, S., Myhre, G., Sayyad, A., & Mataka, S. (2011). Patterned polarized fluorescence from a thin film. Applied Physics Letters, 99(9), 091108. doi:10.1063/1.3631670
• Myhre, G., Sayyad, A., & Pau, S. (2010). Patterned color liquid crystal polymer polarizers. Optics Express, 18(26), 27777-27786.
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  PMID: 21197052;Abstract: We demonstrate patterned polarizers for visible wavelengths using dichroic dye in a liquid crystal polymer (LCP) host. Contact lithography is used to pattern a thin alignment layer, which subsequently transfers the pattern to the LCP. A gray dichroic dye mixture for the visible spectrum is optimized and implemented along with LCP to fabricate this polarizer. A peak extinction ratio of 41 was measured at a 633 nm wavelength, while simultaneously showing patterns as small as 3 μm. Finally, multi layer films are demonstrated by fabricating a two layer patterned circular polarizer consisting of a quarter-wave retarder and a color polarizer. Our process has applications in three-dimensional displays, interferometry, optical storage, and polarimeters. © 2010 Optical Society of America.
• Pau, S., Myhre, G., Sayyad, A., & Pau, S. K. (2010). Patterned color liquid crystal polymer polarizers. Optics express, 18(26).
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  We demonstrate patterned polarizers for visible wavelengths using dichroic dye in a liquid crystal polymer (LCP) host. Contact lithography is used to pattern a thin alignment layer, which subsequently transfers the pattern to the LCP. A gray dichroic dye mixture for the visible spectrum is optimized and implemented along with LCP to fabricate this polarizer. A peak extinction ratio of 41 was measured at a 633 nm wavelength, while simultaneously showing patterns as small as 3 μm. Finally, multi layer films are demonstrated by fabricating a two layer patterned circular polarizer consisting of a quarter-wave retarder and a color polarizer. Our process has applications in three-dimensional displays, interferometry, optical storage, and polarimeters.
• Jiang, L., Myer, B., Tellefsen, K., & Pau, S. (2009). A planar microfabricated electrolyzer for hydrogen and oxygen generation. Journal of Power Sources, 188(1), 256-260.
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  Abstract: We present the design, fabrication and testing of a microfabricated planar reactor for the hydrogen evolution reaction (HER) using thin film Pt electrodes and polydimethylsiloxane (PDMS) fluidic chamber. The reactor is designed to separate gases by flow dynamics and reactor flow is analyzed by three-dimensional finite element analysis. The planar geometry is scalable, compact and stackable. Using KOH 28 wt% electrolyte, we have achieved a hydrogen generation density of 0.23 kg h-1 m-3 and an efficiency of 48% with a flow rate of 10 ml min-1 and cell voltage of 3 V.
• McGovern, S., Harish, G., Pai, C. S., Mansfield, W., Taylor, J. A., Pau, S., & Besser, R. S. (2009). Investigation of multiphase hydrogenation in a catalyst-trap microreactor. Journal of Chemical Technology and Biotechnology, 84(3), 382-390.
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  Abstract: Background: Multiphase hydrogenation plays a critical role in the pharmaceutical industry. A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport. To this end, the small-scale and large surface-to-volume ratios of microreactor technology would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate mass transfer in a catalytic hydrogenation reaction. The reactor design is such that solid catalyst is suspended in the reaction channel by an arrangement of catalyst traps. The design supports the use of commercial catalyst and allows control of pressure drop across the bed by engineering the packing density. Results: This paper discusses the design and operation of the reactor in the context of the liquid-phase hydrogenation of o-nitroanisole to o-anisidine. A two-phase 'flow map' is generated across a range of conditions depicting three flow regimes, termed gas-dominated, liquid-dominated, and transitional, all with distinctly different mass transfer behavior. Conversion is measured across the flow map and then reconciled against the mass transfer characteristics of the prevailing flow regime. The highest conversion is achieved in the transitional flow regime, where competition between phases induces the most favorable gas-liquid mass transfer. Conclusion: The results are used to associate a mass transfer coefficient with each flow regime to quantify differences in performance. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro-scale production reactors. © 2008 Society of Chemical Industry.
• Myhre, G., & Pau, S. (2009). Imaging capability of patterned liquid crystals. Applied Optics, 48(32), 6152-6158.
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  PMID: 19904311;Abstract: We demonstrate the ability to make high resolution arbitrary patterned optical retarders using liquid crystal polymer (LCP). Contact lithography is used to define unique LCP alignment domains. Patterned LCP retarders are imaged between crossed polarizers to determine pattern visibility as a function of feature size. It was determined that patterned retarders for wavelengths between 250nm and 2500nm can be constructed with feature sizes as small as 4 μm. We also showed that multiple patterns can be created on the same substrate using a combination of patterned LCP and opaque features. Our process has applications in displays, double-patterning lithography, and imaging polarimetry. © 2009 Optical Society of America.
• Pau, S., & Dallas, W. J. (2009). Generalized spatial filtering velocimetry and accelerometry for uniform and nonuniform objects. Applied Optics, 48(24), 4713-4722.
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  PMID: 19696860;Abstract: We present a technique to measure velocity, acceleration, and higher order derivatives of motion using periodic and nonperiodic spatial filters. The technique can be applied using a single detector or an array of detectors. In one configuration, the velocity distribution of an object such as a fluid can be measured by imaging the object onto an array of detectors. In another configuration, multiple projections of an object are used to reconstruct a cross-sectional velocity distribution using a tomography algorithm. The advantages and disadvantages of our technique applied to uniform and spatially varying motions are described. © 2009 Optical Society of America.
• Pau, S., Myhre, G., & Pau, S. K. (2009). Imaging capability of patterned liquid crystals. Applied optics, 48(32).
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  We demonstrate the ability to make high resolution arbitrary patterned optical retarders using liquid crystal polymer (LCP). Contact lithography is used to define unique LCP alignment domains. Patterned LCP retarders are imaged between crossed polarizers to determine pattern visibility as a function of feature size. It was determined that patterned retarders for wavelengths between 250 nm and 2500 nm can be constructed with feature sizes as small as 4 microm. We also showed that multiple patterns can be created on the same substrate using a combination of patterned LCP and opaque features. Our process has applications in displays, double-patterning lithography, and imaging polarimetry.
• Lai, W. Y., Ocola, L., & Pau, S. (2008). Focus section on nanofabrication technologies, devices and applications. Journal of Experimental Nanoscience, 3(1), 61-62.
• Jiang, L., & Pau, S. (2007). Integrated waveguide with a microfluidic channel in spiral geometry for spectroscopic applications. Applied Physics Letters, 90(11).
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  Abstract: The authors fabricated and tested a compact optical sensor with an integrated waveguide and a microchannel in spiral geometry. The multimode waveguide, consisting of an SU-8 core of 40 μm thick and 50 μm wide and a fluid cladding layer of 60 μm thick, realizes a light-fluid interaction length of 110 mm within a device area of 4 cm2. The waveguide sensor measures changes in liquid sample concentration and is sensitive to changes in liquid refractive index. Absorbance measurements using the spiral waveguide sensor demonstrate increased sensitivity compared with a linear geometry sensor. © 2007 American Institute of Physics.
• McGovern, S., Harish, G., Pai, C. S., Mansfield, W., Taylor, J. A., Pau, S., & Besser, R. S. (2007). Multiphase flow regimes for hydrogenation in a catalyst-trap microreactor. Chemical Engineering Journal, 135(SUPPL. 1), S229-S236.
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  Abstract: Multiphase reactions, namely gas-liquid reactions involving solid catalyst, play a critical role in many industries. In particular, hydrogenation reactions are carried out on a large scale in the pharmaceutical industry. Nearly 20% all reaction steps in a typical fine chemical synthesis are catalytic hydrogenation. The use of microreactor geometry would greatly benefit chemical process miniaturization in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate multiphase mass transfer in the context of gas-liquid-solid catalytic reactions. The reactor employs a three-channel "catalyst-trap" design, whereby solid catalyst is suspended in the liquid channel by an arrangement of posts. Such a device has advantages in that commercial catalysts are supported, and that pressure drop across the bed can be reduced by engineering the packing density. In this paper, a model incorporating the transport and kinetic effects is developed to design this kind of reactor. We have chosen the liquid-phase hydrogenation of o-nitroanisole to o-anisidine to serve as a prototype reaction. The reaction is carried out across a range of gas and liquid flow rates that encompass three distinct flow regimes, termed gas-dominated, liquid-dominated, and transitional. Variations of the reactor design are used to study the flow regimes in detail. A two-phase "flow map" is generated for each reactor type. Kinetic experiments seek to assign a reaction conversion to each point in this two-phase "flow map," in order to subsequently reconcile differences in performance with the characteristics of the respective flow regime. We observe the highest reaction conversion in the transitional flow regime, where competition between the two phases results in the generation of a large amount of gas-liquid interfacial area. The experimental conversion is greater than that predicted by the initial plug-flow model, an effect attributable to the mass transfer enhancement induced by transitional flow. Flow maps for each reactor variation show that liquid channel dimensions and trap density can be manipulated to maximize the region of transitional flow. In addition, we explore operation at elevated pressures to enhance hydrogen solubility. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macroscale production reactors. © 2007 Elsevier B.V. All rights reserved.
• Pau, S., Whitten, W. B., & Ramsey, J. M. (2007). Planar Geometry for Trapping and Separating Ions and Charged Particles. Analytical Chemistry, 79(17), 6857-6861. doi:10.1021/ac0706269
• Pau, S., Whitten, W. B., & Ramsey, J. M. (2007). Planar geometry for trapping and separating ions and charged particles. Analytical Chemistry, 79(17), 6857-6861.
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  PMID: 17672521;Abstract: A planar quadrupole ion trap is proposed. We have demonstrated an extremely large operating range by trapping ions and particles with mass-to-charge ratio rangingfrom 102 to 109 at frequencies from 2.8 × 106 to 60 Hz at an operating pressure of 1.1 × 10-4 to 760 Torr, respectively, using a trap radius of r1 = 1 mm. We have also performed mass spectrometry with a resolution of 1.2 amu with mass-to-charge range from 50 to 150. Our geometry is simple enough to be integrated into existing integrated circuits and microelectromechanical system devices, opening up the possibility of many novel hybrid applications and experiments. © 2007 American Chemical Society.
• Daly, B. C., Klein, J., Norris, T. B., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2006). Nanoscale coherent acoustic phonon imaging. Proceedings of SPIE - The International Society for Optical Engineering, 6118.
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  Abstract: An ultrafast optical pump and probe technique known as picosecond ultrasonics is used to generate and detect coherent acoustic phonon pulses in nanostructured films grown on Si wafers. By detecting the phonons after they have diffracted across a millimeter thick wafer, it is possible to measure the scattered phonons in the acoustic far field. Numerical backpropagation algorithms can then be used in order to reconstruct the object which scattered the acoustic phonon pulses. We describe measurements and simulations of experiments performed on surface and sub-surface nanostructures. Results with ∼500 nm image resolution are shown, and plans for improving that resolution by an order of magnitude will be described.
• Guo, Z., Quan, H., & Pau, S. (2006). Near-field gap effects on small microcavity whispering-gallery mode resonators. Journal of Physics D: Applied Physics, 39(24), 5133-5136.
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  Abstract: The near-field gap effects are investigated in planar dielectric microdisc and waveguide coupling structures, emphasizing miniaturization of integrated sensor systems. The simulation results show that the resonance frequency is not obviously affected by the gap dimension when the gap between a microcavity and its coupler is larger than 300 nm. However, the resonance frequency shifts observably with a further decreasing gap to the nanometre level. This shift is generally larger than the cavity resonance linewidth in the 10 νm diameter microdisc system, but is comparable to the cavity resonance linewidth in the 2 νm diameter microdisc system. With increasing gap, the cavity Q increases exponentially until it is saturated at a limit Q factor. An optimal gap dimension exists for maximum light energy transfer and storage. The concept of optimum gap is introduced and defined at the gap dimension where half-maximum energy storage capability is achieved; meanwhile, the cavity Q is high and the resonance frequency remains stable. © 2006 IOP Publishing Ltd.
• Guo, Z., Quan, H., & Pau, S. (2006). Numerical characterization of whispering-gallery mode optical microcavities. Applied Optics, 45(4), 611-618.
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  PMID: 16485670;Abstract: We characterize planar microcavities in whispering-gallery mode optical resonances. The microcavity consists of a waveguide and a microdisk, and a nanoscale gap separates the waveguide and the microdisk. The devices can be fabricated on Si-based thin films by using conventional microelectronics techniques. To characterize these types of cavity, we study a broad range of resonator configuration parameters including the size of the microdisk, the width of the gap, and the waveguide dimensions. The finite-element method is used for solving Maxwell's equations. The electric fields and the energy density distributions are obtained and compared between the on-resonance and off-resonance situations. A brilliant ring with a strong electric field and a high-energy density is found inside the periphery of the microdisk under first-order resonance. While under second-order resonance, there are two bright rings, and the light intensity in the inner ring is stronger than that in the outer ring. The resonant frequencies and their free spectral ranges are predominantly determined by the size of the microdisk. The gap effect on the resonant frequencies is observable, although it is minor. The gap strongly affects the full width at half-maximum (FWHM), finesse, and quality factor of the resonances. With an increase in the gap width from 100 to 300 nm, both the Q value and finesse increase substantially, while the FWHM decreases. The waveguide width has a visible influence on the Q value, FWHM, and finesse as well. © 2006 Optical Society of America.
• Klein, J., Norris, T. B., Daly, B. C., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2006). Nanoscale imaging with coherent acoustic phonon pulses. Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, CLEO/QELS 2006.
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  Abstract: We describe ultrafast coherent acoustic phonon measurements of a latent photoresist pattern with 1 μm features that is buried beneath an Al film. Simulation results for higher resolution measurements are also described. © 2006 Optical Society of America.
• McGovern, S., Harish, G., Pai, C. S., Mansfield, W., Taylor, J. A., Pau, S., Besser, R. S., McGovern, S., Gadre, H., Besser, R. S., Pai, C. S., Mansfield, W., & Pau, S. (2006). Catalyst-trap microreactor for hydrogenation of a pharmaceutical intermediate. AIChE Annual Meeting, Conference Proceedings.
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  Abstract: Multiphase hydrogenation reactions involving solid catalyst play a critical role in the pharmaceutical industry. Nearly twenty percent of all reaction steps in a typical fine chemical synthesis are catalytic hydrogenation. Mass and heat transport resistances are generally an obstacle in such reaction systems. The microscale geometry of microreactor technology offers significant gains against these hurdles, hence their use would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate multiphase mass transfer in the context of gas-liquid-solid catalytic reactions. The reactor employs a three-channel "catalyst-trap" design, whereby solid catalyst is suspended in the liquid channel by an arrangement of posts. Such a device supports the use of commercial catalyst, and allows control of pressure drop across the bed by engineering the packing density. This paper discusses the design and operation of the reactor, with the liquid-phase hydrogenation of o-nitroanisole to o-anisidine as a prototype reaction. Experiments are carried out across a range of gas and liquid flow rates that encompasses three distinct flow regimes, termed gas-dominated, liquid-dominated, and transitional. A two-phase "flow map" is generated independent of the reaction to identify the flow regime present at each set of conditions. Reaction experiments assign a conversion to each point in the flow map, in order to subsequently reconcile differences in performance with the characteristics of the respective flow regime. The highest reaction conversion occurs in the transitional flow regime, where competition between the two phases results in the generation of a large amount of gas-liquid interfacial area. Because the experimental conversion is greater than that predicted by the initial plug-flow model, we revise the model to account for the mass transfer enhancement induced by transitional flow. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro-scale production reactors.
• Pau, S., Pai, C. S., Low, Y. L., Moxom, J., Reilly, P. T., Whitten, W. B., & Ramsey, J. M. (2006). Microfabricated quadrupole ion trap for mass spectrometer applications. Physical Review Letters, 96(12).
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  Abstract: An array of miniaturized cylindrical quadrupole ion traps, with a radius of 20 μm, is fabricated using silicon micromachining using phosphorus doped polysilicon and silicon dioxide for the purpose of creating a mass spectrometer on a chip. We have operated the array for mass-selective ion ejection and mass analysis using Xe ions at a pressure of 10-4Torr. The scaling rules for the ion trap in relation to operating pressure, voltage, and frequency are examined. © 2006 The American Physical Society.
• Daly, B. C., Norris, T. B., Chen, J., Khurgin, J. B., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2005). Coherent acoustic phonons in silicon: Propagation studies and imaging applications. Quantum Electronics and Laser Science Conference (QELS), 1, 643-645.
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  Abstract: We generate and detect coherent acoustic phonon pulses in Si using ultrafast optics. A unified model of diffractive, dispersive, and nonlinear propagation effects is developed and verified. Imaging using diffracted phonon pulses shows submicron resolution. © 2005 Optical Society of America.
• Guo, Z., Quan, H., & Pau, S. (2005). Gap effects on whispering-gallery mode microresonances. Proceedings of SPIE - The International Society for Optical Engineering, 6002.
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  Abstract: Photon tunneling between an optical resonator and a light-delivery coupler is strongly dependent on the gap dimension which can vary from zero to size of an optical wavelength involved. In this systematic report, we investigate the gap effects of whispering-gallery modes in two modeling systems: a waveguide-coupling resonator of 2μm and l0μm in diameter, respectively. Maxwell's equations which govern the EM wave propagation and photon tunneling in the microsystems are solved using the finite element method. The simulation accuracy and sensitivity is examined. It is found that when the maximum element size in the computationally sensitive regions is below 1/8 of the wavelength involved, the calculations are accurate. An optimal gap exists for maximum energy coupling and is a strong function of the wavelength of the resonant mode. The Q factor increases exponentially with increasing gap and saturates as the gap approaches the optical wavelength. An optimum gap can be defined at the half maximum energy coupling where both the Q factor and coupling efficiency are high. We also calculate the effects of gap width on the resonance shift. We find that the resonance wavelength is increased (decreased) with decreasing gap width for the 10μm (2μm) diameter resonator with narrow gap widths.
• Guo, Z., Quan, H., & Pau, S. (2005). Optical resonance in fabricated whispering-gallery mode microcavity. Journal of Heat Transfer, 127(8), 808-.
• Kim, J., Pau, S., Ma, Z., McLellan, H. R., Gates, J. V., Kornblit, A., Slusher, R. E., Jopson, R. M., Kang, I., & Dinu, M. (2005). System design for large-scale ion trap quantum information processor. Quantum Information and Computation, 5(7), 515-537.
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  Abstract: We present a detailed system design and available technology choices for building a large scale (> 100 qubits) ion trap quantum information processor (QIP). The system design is based on technologies that are within reach today, and utilizes single-instruction-on-multiple-data (SIMD) principles to re-use resources that cannot be duplicated easily. The system engineering principles adopted highlight various design tradeoffs in the QIP design and serve as a guideline to find design spaces for a much larger QIP. © Rinton Press.
• Lai, W. Y., Ocola, L. E., & Pau, S. (2005). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 6002, xi-xii.
• Lai, W. Y., Pau, S., & López, O. D. (2005). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 5592, xiii-xiv.
• Norris, T. B., Daly, B. C., Jing, C., Khurgin, J., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2005). Nanoacoustics: Propagation and imaging with THz coherent phonons. IQEC, International Quantum Electronics Conference Proceedings, 2005, 1550-1551.
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  Abstract: We investigate experimentally and theoretically the propagation of coherent acoustic phonon pulses generated in Si using ultrafast optical pulses. These acoustic pulses are shown to be applicable for two-dimensional nanoscale imaging.
• Ouyang, X., Bednarova, L., Chen, H., Pau, S., Lawal, N., Lee, W. Y., & Besser, R. S. (2005). Comparisons between a thin-film catalyzed microreactor and conventional lab reactors for PrOx kinetic studies. 2005 AIChE Spring National Meeting, Conference Proceedings, 2917-2926.
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  Abstract: In our study of CO preferential oxidation (PrOx) on Pt/Al 2O 3 with a thin-film catalyzed microreactor, systematic differences of kinetic study results and characteristic curves of CO conversion were identified between the microreactor and conventional minimized packed-bed lab reactors (m-PBR's). Evidence suggested that the difference in heat transport limitations is the origin of these differences. In this paper, these differences were examined systematically. First, based on existing criteria for mass and heat transport limitations, we found negligible mass transport resistance for both types of reactors within typical PrOx operating conditions, but strong heat transport limitations for m-PBR's. Further, a non-isothermal reactor model was built to quantitatively study the effect of the heat transport limitations on PrOx reaction behavior. Model results showed that the temperature gradients in m-PBR's favor the r-WGS reaction, thus causing a much narrower range of permissible operating temperature compared to the microreactor. Accordingly, a more direct access to PrOx reaction kinetics is permitted by the microreactor because of its excellent heat transfer efficiency.
• Pau, S. (2005). Trapping and separating polar molecules by a hexapole trap. Applied Physics Letters, 87(13), 1-3.
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  Abstract: A technique to trap and separate particle of different dipole moment using a hexapole potential is presented. The operation is similar to the method of ion trap mass spectrometer in that the trajectory of a dipole can be described by Mathieu equation. The technique can also be generalized to trap particle of higher order moment by including higher multipole components in the design of the potential. © 2005 American Institute of Physics.
• Quan, H., Guo, Z., Lei, X. u., & Pau, S. (2005). Design, fabrication and characterization of whispering-gallery mode miniature sensors. Proceedings of SPIE - The International Society for Optical Engineering, 5592, 373-381.
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  Abstract: In this paper, we present the design, fabrication and characterization of the whispering-gallery mode (WGM) miniature sensors for potential use in biosensing at the nanometer scale. In order to understand and investigate the characteristics of WGM resonances, we designed and fabricated a number of sensors with different dimensions. Each sensor is a micro/nano-structure consisted of a microdisk as the resonating cavity and a micro waveguide for light delivery and collection. In addition to the waveguides having uniform cross-section dimensions, tapered waveguide was also considered in our studies. A simulation model was employed to characterize the EM field and radiation energy density of the designed sensors. The gap effects on WGM resonance in terms of quality factor and full width at half maximum (FWHM) were evaluated. Following the design and characterization, the sensors were fabricated in 1.μm-thick Si 3N 4 film using 248nm optical lithography and conventional silicon IC processing. Top and down SEM measurements of the fabricated sensors were conducted and the data for the sensors in one device are given.
• Daly, B. C., Holme, N. C., Branciard, C., Norris, T. B., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2004). Nanostructure imaging with sub-THz coherent acoustic phonon pulses. OSA Trends in Optics and Photonics Series, 97, 159-160.
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  Abstract: We describe a novel imaging technique that employs coherent acoustic phonon pulses which are generated and detected by ultrafast optical methods. Sub-micron resolution images of Al lines lithographically etched on a Si substrate are shown. © 2003 Optical Society of America.
• Daly, B. C., Holme, N. C., Buma, T., Branciard, C., Norris, T. B., Pau, S., Tennant, D. M., Taylor, J. A., & Bower, J. E. (2004). Imaging nanostructures with picosecond ultrasonic pulses. Springer Series in Chemical Physics, 79, 231-235.
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  Abstract: We describe a novel imaging technique that employs coherent acoustic phonon pulses which are generated and detected by ultrafast optical methods. Sub-micron resolution images of A1 patterns lithographically etched on a Si substrate are shown.
• Daly, B. C., Holme, N. C., Buma, T., Branciard, C., Norris, T. B., Tennant, D. M., Taylor, J. A., Bower, J. E., & Pau, S. (2004). Imaging nanostructures with coherent phonon pulses. Applied Physics Letters, 84(25), 5180-5182.
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  Abstract: The use of picosecond acoustic phonon pulses for the nanoscale acoustic imaging was analyzed. Nanoscale acoustic imaging was use to characterize the nanomaterials and nanoelectronic devices, and also for acoustic cryomicroscopy of biological samples. The ultrafast optical pulses were used to generate high-frequency acoustic pulses by impulsive thermoelastic excitation of a patterned 15-nm-thick metal films on a crystalline substrate. The 1-micron-period Al structures on Si, which was lithographically defined, was used to characterize the image resolution.
• Kornblit, A., Aksyuk, V. A., Bogart, G. R., Bolle, C., Bower, J. E., Cirelli, R. A., Ferry, E., Fetter, L., Gasparyan, A., Greywall, D. S., Keller, R. C., Klemens, F. P., Lai, W. Y., Lopez, O. D., Mansfield, W. M., Miner, J. F., Pai, C. -., Pardo, F., Pau, S., , Simon, M. E., et al. (2004). Processing challenges in the fabrication of advanced MEMS. Proceedings - Electrochemical Society, 9, 11-25.
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  Abstract: As higher performance and complexity is demanded from advanced MEMS, the processes required to fabricate them are becoming much more demanding. Sub-micron features, rarely found in early MEMS, are now needed for unproved performance. Advanced processes, relying on tools that are available for high-performance ICs, can be used to achieve the desired functionality of advanced MEMS. This paper focuses mainly on devices in the optical domain, but the techniques to fabricate them are common to all MEMS.
• Pau, S., Taylor, J. A., & Pai, C. S. (2004). Nonorthogonal wafer dicing for waveguide, microelectromechanical systems, and nanotechnology applications. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 22(4), L15-L16.
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  Abstract: A technique to dice wafer was analyzed by using photolithography and reactive ion etching. The photoresists were used as a mask to protect the underlying device during the etching. It was observed that typical wafer cutting required a spacing of the order of about 100 μm. It was also observed that this technique could be used to cut very small die with almost any conceivable shape subject to the limitations of dry etching.
• Quan, H., Guo, Z., & Pau, S. (2004). Parametric studies of whispering-gallery mode resonators. Proceedings of SPIE - The International Society for Optical Engineering, 5593, 593-602.
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  Abstract: This report characterizes the whispering-gallery mode (WGM) resonators with the design of waveguide and microdisk coupling microstructure. In order to understand and optimize the design, studies over a broad range of resonator configuration parameters including the microdisk size, the gap separating the microdisk and waveguide, and the waveguide width are numerically conducted. The finite element method is used for solving the Maxwell's equations which govern the propagation of electromagnetic (EM) field and the radiation energy transport hi the micro/nano-structured WGM systems. The EM field and the radiation energy distributions in the WGM resonator are obtained and compared between the on-resonance and off-resonance cases. A very brilliant ring with strong EM field and high radiation intensity is found inward the peripheral surface of the microdisk under the first-order resonance. While under the second-order resonance, there are two bright rings; and the outer ring inward the peripheral surface is thin and weaker than the internal ring. The microdisk size affects significantly the resonant frequencies and their intervals. The gap also has a slight effect on the resonant frequencies. The effect of waveguide width on the resonant frequencies is negligible. However, the gap as well as the waveguide width does obviously influence the qualify factor and the finesse of the resonant modes.
• Pau, S., Angelis, M. D., & Holland, B. (2003). Time-multiplexed signals and parallel signal analysis/switch optimization for MEMS-based optical cross-connect. Journal of Lightwave Technology, 21(3), 609-613.
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  Abstract: The calibration of the numerous mirror pairs, or switches, in MEMS-mirror optical cross-connect systems is a critical process in their manufacture. Because the number of switch connections for these systems scales quadratically to the number of inputs/outputs, this places great demands on the equipment used to perform testing. We propose and demonstrate a calibration technique for generic optical subsystems based on optical time-division multiplexing (OTDM).
• Pau, S., Chand, N., Kojima, K., & Swaminathan, V. (2003). Transient effects and cascadability of an MEMS-based dynamic-gain equalizing filter: A case study. IEEE Photonics Technology Letters, 15(2), 347-349.
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  Abstract: We investigate the cascadability and transient effects of an micro-electromechanical-systems-based 64-channel blocker. We observe no transient effect due to the blocker. We limited our study to ten cascades and observe negligible optical power penalty with or without the 7-dB maximum allowable equalization for both nonreturn-to-zero and return-to-zero pulses.
• Graebner, J. E., Pau, S., & Gammel, P. L. (2002). All-optical excitation and detection of microelectrical-mechanical systems. Applied Physics Letters, 81(19), 3531-3533.
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  Abstract: The radiation pressure of a chopped, 3 mW optical beam is used to excite angular motion of a Microelectrical-mechanical-systems' (MEMS) mirror at its resonant frequencies. The modes are identified with a scanning interferometer, providing an all-optical excitation/detection scheme. The resonant frequencies, mode distributions, spring constants, and coupling between adjacent MEMS devices can, therefore, be studied without the use of electrostatic or other types of actuation. Within the experimental error of ∼30%, the amplitude of angular oscillation is equal to the theoretical value expected for radiation pressure. © 2002 American Institute of Physics.
• Pau, S., Jianjun, Y. u., Kojima, K., Chand, N., & Swaminathan, V. (2002). 160-Gb/s all-optical MEMS time-slot switch for OTDM and WDM applications. IEEE Photonics Technology Letters, 14(10), 1460-1462.
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  Abstract: The authors propose and successfully demonstrate a novel, simple, and low-cost concept of optical time-slot switching, i.e., switching part of one 160-Gb/s optical time-division multiplexing channel to another 160 Gb/s channel all in optical domain without any optical-electrical-optical conversion and with negligible power penalty.
• Ryf, R., Neilson, D. T., Kolodner, P. R., Kim, J., Hickey, J. P., Carr, D., Aksyuk, V., Greywall, D. S., Pardo, F., Bolle, C., Frahm, R., Basavanhally, N. R., Ramsey, D. A., George, R., Kraus, J., Lichtenwalner, C., Papazian, R., Nuzman, C., Weiss, A., , Kumar, B., et al. (2002). Multi-service optical node based on low-losers MEMS optical crossconnect switch. Conference on Optical Fiber Communication, Technical Digest Series, 70, 410-411.
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  Abstract: A multi-service node based on an optical microelectromechanical (MEMS) crossconnect switch with 1.33 dB mean loss was demonstrated. Low loss optical switches could be combined with other optical components to build highly adaptable multiservice devices. A flexible Add/Drop multiplexer was implemented by connecting the output ports of two 16-channel freespace grating-based demultiplexing to switch ports.
• Pau, S., Watson, G. P., & Nalamasu, O. (2001). Writing an arbitrary non-periodic pattern using interference lithography. Journal of Modern Optics, 48(7), 1211-1223.
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  Abstract: We propose a technique to write non-periodic patterns using interference lithography. Arbitrary patterns in one and two dimension are constructed by continuous scanning of multiple coherent sources at various incident angles and intensities.
• Ryf, R., Bernasconi, P., Kolodner, P., Kim, J., Hickey, J. P., Carr, D., Pardo, F., Bolle, C., Frahm, R., Basavanhally, N., Yoh, C., Ramsey, D., George, R., Kraus, J., Lichtenwalner, C., Papazian, R., Gates, J., Shea, H. R., Gasparyan, A., , Muratov, V., et al. (2001). Scalable wavelength-selective crossconnect switch based on MEMS and planar waveguides. European Conference on Optical Communication, ECOC, 6, 76-77.
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  Abstract: A 72×72 wavelength-selective crossconnect switch that was scalable to 1296×1296 with available planar waveguide and MEMS technology, was demonstrated. Silica-on-silicon wavelength multiplexers with integrated monitoring taps and a MEMS micromirror array were assembled in a hybrid three dimensional beam steering crossconnects. The switch operated penalty free at 10 Gbit/s and provided integrated power monitoring taps.
• Ryf, R., Kim, J., Hickey, J. P., Gnauck, A., Carr, D., Pardo, F., Bolle, C., Frahm, R., Basavanhally, N., Yoh, C., Ramsey, D., Bole, R., George, R., Kraus, J., Lichtenwalner, C., Papazian, R., Gates, J., Shea, H. R., Gasparyan, A., , Muratov, V., et al. (2001). 1296-port MEMS transparent optical crossconnect with 2.07Petabit/s switch capacity. Conference on Optical Fiber Communication, Technical Digest Series, 54(4), PD28/1-PD28/3.
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  Abstract: A 1296-port MEMS transparent optical crossconnect with 5.1dB+/-1.1dB insertion loss at 1550nm is reported. Measured worst-case optical crosstalk in a fabric was ñ38dB and nominal switching rise/fall times were 5msec. A 2.07Petabit/s switch capacity was verified upon cross-connecting a forty-channel by 40Gb/s DWDM data stream through a prototype fabric.
• Griffith, J. E., Kneedler, E. M., Ningen, S., Berghaus, A., III, C. B., Pau, S., Houge, E., & Shofner, T. (2000). Scanning probe metrology in the presence of surface charge. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 18(6), 3264-3267.
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  Abstract: The operation of a scanning force microscope that is relatively immune to charge-induced forces while allowing the probe tip to nondestructively follow the surface topography is discussed. A servoed force-balance sensor is incorporated in the instrument. The sensor responded to forces associated with the solid surfaces and not to the forces arising from charging or contamination.
• Pau, S., Bolan, K., Blakey, M., & Nalamasu, O. (2000). Shape engineering: A novel optical proximity correction technique for attenuated phase-shift mask. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 18(6), 2896-2899.
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  Abstract: The minimization of sidelobe printability and maximization of latitude and resolution in attenuated phase shift masks (APSM) was studied theoretically and experimentally. The modification of shapes and relative orientations in contact windows was also presented. The results showed the obtaining of sidelobe suppression with no loss in process latitude and resolution.
• Pau, S., Cirelli, R., Bolan, K., Timko, A. G., Frackoviak, J., Watson, G. P., Trimble, L. E., Blatchford, J. W., & Nalamasu, O. (2000). High density lithography using attenuated phase shift mask and negative resist. Proceedings of SPIE - The International Society for Optical Engineering, 4000, I/-.
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  Abstract: A technique to print high-density windows using attenuated phase shift mask, negative photoresist and ArF exposure tool is demonstrated. The technique can be implemented types. It use sub-wavelength features and offers higher packing density compared with the use of binary masks and positive photoresists.
• Pau, S., Nalamasu, O., Cirelli, R., Frackoviak, J., Timko, A., Watson, G. P., Klemens, F., & Timp, G. (2000). Sub-wavelength printing using multiple overlapping masks. Microelectronic Engineering, 53(1), 119-122.
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  Abstract: A multiple exposure technique is used to print various types of patterns with critical dimensions much smaller than the wavelength of light used for exposure. The process latitude of the exposure can be very large because it is limited by the large pattern of the individual mask and not by the critical dimension of the small feature.
• Pau, S., Nalamasu, O., Cirelli, R., Frackoviak, J., Timko, A., Watson, P., Klemens, F., & Timp, G. (2000). Wavelength-independent optical lithography. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 18(1), 317-320.
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  Abstract: A multiple exposure photolithographic technique is presented. The resolution of the technique is limited not by exposure wavelength but by processing. This optical lithography was implemented by multiple exposures with two etchings and with single etching. The resulting positive resists started with a bare wafer with a 1000 A oxide atop. The wafer was coated with resist and was exposed to the first mask. Plasma etching was applied twice until the final pattern was achieved.
• Pau, S., Trimble, L. E., Blatchford, J. W., Watson, G. P., Frackoviak, J., Cirelli, R., & Nalamasu, O. (1999). Focus drilling and attenuated phase shift mask for subwavelength contact window printing using positive and negative resists. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 17(6), 2499-2506.
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  Abstract: We have investigated the process latitude and resolution limit of printing contact windows using a high numerical aperture KrF stepper and attenuated phase shift mask (APSM). We show that both . positive and negative resists can be used depending on the size of the window on the mask. The advantages and disadvantages of using the positive and negative resists are presented. A combination of APSM and focus drilling are shown to extend the focus latitude of subwavelength window printing. © 1999 American Vacuum Society.
• Liu, Z. X., Pau, S., Syassen, K., Kuhl, J., Kim, W., Morkoç, H., Khan, M. A., & Sun, C. J. (1998). Photoluminescence and reflectance studies of exciton transitions in wurtzite GaN under pressure. Physical Review B - Condensed Matter and Materials Physics, 58(11), 6696-6699.
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  Abstract: We have measured photoluminescence (PL) and reflectance spectra of high-quality wurtzite GaN on sapphire at pressures up to 8 GPa (T = 10 K). All three intrinsic exciton transitions arising from the A, B, and C interband transitions were observed in reflectance measurements. The PL spectra are dominated by the A and B free exciton transitions and the recombination of an exciton bound to a neutral donor. Transitions due to the excited n = 2 state of the A exciton and the first- and second-order LO phonon replicas of the A free exciton were also resolved. The pressure dependence of the A band gap and exciton binding energy is obtained from the intrinsic exciton energies. The experimental results clearly reveal a sample-dependent change of the biaxial strain in the GaN layers with increasing hydrostatic pressure.
• Pau, S., Kuhl, J., Khan, M. A., & Sun, C. J. (1998). Application of femtosecond-excitation correlation to the study of emission dynamics in hexagonal GaN. Physical Review B - Condensed Matter and Materials Physics, 58(19), 12916-12919.
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  Abstract: We perform time- and spectrally resolved femtosecond-excitation correlation (FEC) on hexagonal GaN at 10 K. A general procedure to interpret the FEC signal at the exciton energies is presented. By fitting to a rate equation model, we find the bimolecular formation coefficient of the GaN A exciton to be C=1.2 ×10-18 cm3 ps-1. © 1998 The American Physical Society.
• Pau, S., Kuhl, J., Scholz, F., Haerle, C., Khan, M. A., & Sun, C. J. (1998). Study of hexagonal GaN by femtosecond-excitation correlation measurement and degenerate four-wave-mixing. Springer Series in Chemical Physics, 63, 251-253.
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  Abstract: Carrier and exciton dynamics in bulk hexagonal GaN is studied spectrally and temporally by correlation and degenerate four-wave-mixing techniques for different excitation density, wavelength and temperature.
• Pau, S., Kuhl, J., Scholz, F., Haerle, V., Khan, M. A., & Sun, C. J. (1998). Measurement of phonon-exciton dephasing rate in GaN on sapphire by degenerate four-wave mixing. Applied Physics Letters, 72(5), 557-559.
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  Abstract: The density and temperature dependence of the exciton dephasing time of two hexagonal GaN films on sapphire is measured using degenerate four-wave mixing (DFWM). The residual 4 ps dephasing time at low temperature and density is caused by exciton-impurity scattering. We present a theory of DFWM for various amount of inhomogeneous broadening. Good agreement of the temperature dependence of the dephasing time is found between theory and experiment. © 1998 American Institute of Physics.
• Pau, S., Liu, Z. X., Kuhl, J., Ringling, J., Grahn, H. T., Khan, M. A., Sun, C. J., Ambacher, O., & Stutzmann, M. (1998). Time-resolved photoluminescence study of excitons in hexagonal GaN layers grown on sapphire. Physical Review B - Condensed Matter and Materials Physics, 57(12), 7066-7070.
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  Abstract: We performed time-resolved and continuous wave photoluminescence on two samples of hexagonal GaN, one with free exciton emission and the other without. For the sample with free exciton emission, very different decay dynamics are observed between the front and backside emission. We find that the strain caused by the lattice mismatch between the sapphire substrate and the GaN film has a large influence on the population decay of the sample with free exciton emission and a minor influence on the decay properties of the sample dominated by bound exciton emission. A polariton picture is used to describe the observed behavior.
• Cao, H., Klimovitch, G., Björk, G., Pau, S., & Yamamoto, Y. (1997). Tunneling spectroscopy for quantum well excitons. Applied Physics Letters, 70(15), 1986-1988.
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  Abstract: We have demonstrated a technique of directly measuring the exciton binding energy and the valence band split in the quantum well through a tunneling process. We have also measured the emission efficiency of quantum well heavy-hole excitons and light-hole excitons into the normal direction. © 1997 American Institute of Physics.
• Cao, H., Pau, S., Jacobson, J. M., Björk, G., Yamamoto, Y., & Imamoǧlu, A. (1997). Transition from a microcavity exciton polariton to a photon laser. Physical Review A - Atomic, Molecular, and Optical Physics, 55(6), 4632-4635.
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  Abstract: In a previous paper [Phys. Rev. A 54, R1789 (1996)], we reported the observation of a laserlike transition in a single GaAs quantum well microcavity and gave the interpretation as spontaneous buildup of coherent exciton-polariton population via stimulated polariton-phonon emission. In this Brief Report, we present new experimental data and correct our previous interpretation for the microcavity polariton system at high density. We observe a continuous transition from a microcavity polariton emission to a bare photon laser. This conclusion is based on the measurements of the angular resolved photoluminescence, linewidth, and intensity of the lasing line as well as the reflection spectrum under cw pumping.
• Pau, S., Björk, G., Cao, H., Tassone, F., Huang, R., Yamamoto, Y., & Stanley, R. P. (1997). LO-phonon-enhanced microcavity polariton emission. Physical Review B - Condensed Matter and Materials Physics, 55(4), R1942-R1945.
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  Abstract: We observe resonant enhancement of the microcavity exciton-polariton emission by more than three orders of magnitude when the excitation laser is tuned to a single longitudinal-optical-phonon energy above the polariton energies. Our finding provides a scheme to efficiently populate K∥=0 polaritons which bypasses the slow-acoustic-phonon thermalization process.
• Pau, S., Kuhl, J., Scholz, F., Haerle, V., Khan, M. A., & Sun, C. J. (1997). Femtosecond degenerate four-wave mixing of GaN on sapphire: Measurement of intrinsic exciton dephasing time. Physical Review B - Condensed Matter and Materials Physics, 56(20), R12718-R12721.
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  Abstract: We describe time-integrated and spectrally resolved degenerate four-wave mixing (DFWM) on hexagonal GaN on sapphire for different laser energies and intensities. Our measured DFWM signal decays exhibit no contributions originating from polariton propagation effects in the 1- to 3-μm-thick bulk samples or from exciton/free-carrier scattering. At low temperatures and low excitation intensities the dephasing time of the A exciton is as long as 3 ps and is most likely due to scattering by defects. At excitation densities above Nex = 5 × 1015 cm-3 exciton-exciton scattering becomes the dominant dephasing mechanism and a fifth-order diffraction signal is observed above Nex = 3 × 1016 cm-3. © 1997 The American Physical Society.
• Stanley, R. P., Pau, S., Oesterle, U., Houdré, R., & Ilegems, M. (1997). Resonant photoluminescence of semiconductor microcavities: The role of acoustic phonons in polariton relaxation. Physical Review B - Condensed Matter and Materials Physics, 55(8), R4867-R4870.
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  Abstract: We have measured the resonantly excited photoluminescence (PL) from a semiconductor microcavity. At 30 K the form of the PL spectra is almost independent of excitation wavelength while at 5 K the spectra change shape depending on the excitation. We attribute this difference to the transition from multiple to single acoustic phonon scattering. An elementary model is given which agrees with the data using only the temperature as a free parameter. The results show the important role that acoustic phonons play in exciton (cavity polariton) thermalization at low temperature (T=5-30 K) and density (n=107-109 cm-2).
• Björk, G., Pau, S., Jacobson, J. M., Cao, H., & Yamamoto, Y. (1996). Effect of dephasing on exciton superradiance and exciton cavity polaritons. Journal of the Optical Society of America B: Optical Physics, 13(5), 1069-1077.
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  Abstract: Quantum-well exciton superradiance and exciton cavity polarization formation both require a substantial spatial coherence area in order to become the dominant exciton field interaction. In both interaction processes the quantum-well (in-plane) momentum is conserved. Momentum scattering, which is due, e.g., to interaction with a phonon reservoir, quickly localizes an initially delocalized exciton and randomizes the excitation momentum. We take a close look at how momentum scattering influences measurements of excitonic superradiance and of exciton cavity polariton splitting. An important conclusion is that, in general, measurements of the emitted light do not correspond to the evolution of the system as a whole. Therefore, e.g., the measured decay rates do not correspond to the true decay rate of the system. © 1996 Optical Society of America.
• Cao, H., Pau, S., & Yamamoto, Y. (1996). Observation of exciton-polariton ladder in semiconductor microcavity. Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series, 9, 33-34.
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  Abstract: Control of spontaneous emission in a semiconductor microcavity has attracted a lot of interest and investigation, as a result of its fundamental cavity QED aspects and its application to low threshold or even thresholdless lasers. The authors have investigated the case where many exciton modes couple with single cavity photon mode. Theoretical calculation shows that when the separation between adjacent exciton mode is much larger than the Rabi splitting of one exciton mode with the photon mode, the photon mode will couple with only one exciton mode at a time, and the dispersion curves show many anti-crossings. However, if the exciton mode separation is much smaller than the exciton-polariton coupling, the photon mode will couple with several exciton modes simultaneously. The Rabi splitting will be clamped by mode separation, and the anti-crossing of the dispersion curve is diminished.
• Cao, H., Pau, S., Yamamoto, Y., & Björk, G. (1996). Exciton-polariton ladder in a semiconductor microcavity. Physical Review B - Condensed Matter and Materials Physics, 54(11), 8083-8086.
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  Abstract: We investigated the strongly coupled single cavity photon state and multiple discrete quantum-well exciton states in a semiconductor microcavity. The measured exciton-polariton dispersion curves feature multiple anticrossing. The theoretical simulation is in good agreement with the experimental result.
• Imamoglu, A., Ram, R. J., Pau, S., & Yamamoto, Y. (1996). Nonequilibrium condensates and lasers without inversion: Exciton-polariton lasers. Physical Review A - Atomic, Molecular, and Optical Physics, 53(6), 4250-4256.
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  Abstract: We analyze elementary properties of exciton and polariton lasers - devices that generate coherent optical and matter waves using final-state stimulation of exciton-phonon scattering. First we discuss the relation between the conditions for the onset of equilibrium and nonequilibrium excitonic condensates. Provided that the thermal de Broglie wavelength λT exceeds the exciton Bohr radius aB, an exciton laser operates without electronic population inversion. In contrast to previous proposals, this is a different type of laser without inversion which utilizes many-body coherences. When the excitonic character of the polariton branch vanishes, a polariton laser becomes indistinguishable from a photon laser.
• Pau, S., Björk, G., Cao, H., Hanamura, E., & Yamamoto, Y. (1996). Theory of inhomogeneous microcavity polariton splitting. Solid State Communications, 98(9), 781-784.
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  Abstract: A quantum theory of microcavity exciton polariton for an inhomogeneous distribution of exciton is presented for the linear excitation regime. Calculations show that the apparent vaccum Rabi splitting is reduced when the inhomogeneous linewidth exceeds the intrinsic splitting without inhomogeneous broadening. Copyright © 1996 Published by Elsevier Science Ltd.
• Pau, S., Björk, G., Jacobson, J., & Yamamoto, Y. (1996). Fundamental thermodynamic limit of laser efficiency. IEEE Journal of Quantum Electronics, 32(3), 567-572.
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  Abstract: The thermodynamic limits on the efficiency of different types of lasers are calculated both classically and quantum mechanically. In the classical case, the limit is derived from the inequality provided by the population inversion. In the quantum mechanical case, the limit is derived from the inequality of the change of entropy. The Shannon and von Neuman entropies of different light states are worked out.
• Pau, S., Cao, H., Jacobson, J., Björk, G., Yamamoto, Y., & Imamoǧlu, A. (1996). Observation of a laserlike transition in a microcavity exciton polariton system. Physical Review A - Atomic, Molecular, and Optical Physics, 54(3), R1789-R1792.
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  Abstract: We present experimental evidence of spontaneous buildup of coherent exciton polariton population in a microcavity, i.e., an exciton polariton laser. The laser phase transition was confirmed by the increased differential quantum efficiency and decreased linewidth of the lasing polariton mode due to onset of final-state stimulations and the decreased differential quantum efficiency of a nonlasing polariton due to onset of gain clamping at threshold. The exciton polariton laser is distinctly different from an optical laser because of its density-dependent scattering mechanism. The rate equations, taking into account phonon-assisted polariton emission and the polariton-reservoir exciton scattering rate, explain the measurement results well.
• Pau, S., Jacobson, J., Björk, G., & Yamamoto, Y. (1996). Phonon-assisted exciton-polariton emission in a microcavity. Journal of the Optical Society of America B: Optical Physics, 13(5), 1078-1084.
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  Abstract: Quantum-well excitons in a semiconductor microcavity are studied by photoluminescence and input-output experiments. Emission peaks at both longer and shorter wavelengths are observed, indicating the importance of exciton-acoustic-phonon interaction at low temperature. Pump-probe experiments show that the probe beam can be either amplified or attenuated, depending on the energies of the pump and the probe. The dynamics of this process are described by a simple rate-equation model. © 1996 Optical Society of America.
• Bjork, G. G., Cao, H., Jacobson, J., Pau, S., & Yamamoto, Y. (1995). Microcavity laser physics. Proceedings of SPIE - The International Society for Optical Engineering, 2399, 538-551.
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  Abstract: Microcavity lasers have been predicted to offer low threshold current, high quantum efficiency and high modulation bandwidth. In this report we review the physics underlying microcavity device behavior. Specifically we cover dipole-field coupling for both localized (point) dipoles and extended dipoles. In general, optical pumping of the devices is required to create extended dipoles. We also outline the difference between the weak (irreversible) coupling regime and the strong (reversible) regime. For photonic application the intermediate, superradiant regime is perhaps more interesting than the strong coupling regime. Finally, we describe our recent experimental efforts to make high quantum efficiency devices by creating extended excitonic dipoles in electrically pumped devices.
• Björk, G., Pau, S., Jacobson, J. M., Cao, H., & Yamamoto, Y. (1995). Excitonic superradiance to exciton-polariton crossover and the pole approximations. Physical Review B, 52(24), 17310-17320.
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  Abstract: We examine the relationship between atomic and excitonic superradiance in thin and thick slab geometries. We demonstrate that superradiance can be treated by a unified formalism for atoms, Frenkel excitons, and Wannier excitons. It is well known that in sufficiently thick slabs, the normal modes of the system are polaritons, a superposition of the slab exciton, and photon modes. We specifically examine the crossover from superradiance to polariton modes and derive both the crossover slab length and the maximum superradiative decay rate. We show that the exciton and polariton pole approximations, which give simple expressions for superradiance and polariton mode decay rates, give excellent agreement with the exact expressions for the pertinent thicknesses for which the approximations are valid. © 1995 The American Physical Society.
• Cao, H., Jacobson, J., Björk, G., Pau, S., & Yamamoto, Y. (1995). Observation of dressed-exciton oscillating emission over a wide wavelength range in a semiconductor microcavity. Applied Physics Letters, 1107-.
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  Abstract: We have observed the dressed-exciton oscillating emission in the time domain and the associated spectral splitting in the frequency domain from a GaAs single quantum well microcavity over a very broad range of cavity resonant wavelengths. The spectral splitting and temporal oscillation period have been measured to be nearly constant over two orders of magnitude variation of pump intensity, which confirms the linear bosonic feature of Wannier excitons in the weak excitation regime.© 1995 American Institute of Physics.
• Jacobson, J., Pau, S., Cao, H., Bjork, G., & Yamamoto, Y. (1995). Observation of exciton-polariton oscillating emission in a single-quantum-well semiconductor microcavity. Physical Review A - Atomic, Molecular, and Optical Physics, 51(3), 2542-2544.
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  Abstract: The exciton-polariton oscillating emission was directly observed in a single-quantum-well system. These findings supported the view that recently observed thresholdless coherent emission is not resonant Rayleigh scattering but rather an exciton-polariton emission. A measurement of the phase between the exciton and the photon modes constituting the polariton was made by means of a zero of time marker. The natural physical interpretation was provided in terms of a modified atom resonance due to its strong coupling to a cavity vacuum field. It was also confirmed that the regime was of weak excitation by noting that the turn-on delay time between creation of the exciton ensemble and the emission peak of photons is invariant over a three order of magnitude variation in the pump intensity.
• Pau, S., Björk, G., Jacobson, J., & Yamamoto, Y. (1995). Phonon-polariton interaction in a microcavity. Il Nuovo Cimento D, 17(11-12), 1657-1662.
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  Abstract: The linewidth of the microcavity exciton polariton is studied by onresonant and off-resonant photoluminescences. The two main contributions to the linewidth are caused by radiative loss and phonon scattering. The oscillator strength is found to be unmodified by the exciton-phonon coupling. Comparison is made between theory and experiment. © 1995 Società Italiana di Fisica.
• Pau, S., Björk, G., Jacobson, J., Cao, H., & Yamamoto, Y. (1995). Microcavity exciton-polariton splitting in the linear regime. Physical Review B, 51(20), 14437-14447.
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  Abstract: Comparisons are made of a classical and a quantum mechanical model of polariton energy splitting inside a microcavity in the linear excitation regime. Analytical expressions are obtained for the splitting energy as a function of temperature, detuning, and exciton-photon coupling constants. Experimental results are compared with theory, and agreements are found only if the effect of inhomogeneity is taken into account. © 1995 The American Physical Society.
• Pau, S., Björk, G., Jacobson, J., Cao, H., & Yamamoto, Y. (1995). Stimulated emission of a microcavity dressed exciton and suppression of phonon scattering. Physical Review B, 51(11), 7090-7100.
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  Abstract: The threshold behavior of the stimulated parametric emission of dressed excitons in a microcavity is studied. The inelastic-phonon-scattering rates of the dressed exciton are calculated and are shown to be smaller than the bare quantum-well exciton values. The results describe the recently observed thresholdless photoemission behavior and predict a large stability for the dressed exciton modes inside a quantum-well microcavity. © 1995 The American Physical Society.
• Björk, G., Pau, S., Jacobson, J., & Yamamoto, Y. (1994). Wannier exciton superradiance in a quantum-well microcavity. Physical Review B, 50(23), 17336-17348.
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  Abstract: Excitonic superradiance has been predicted to induce a rapid decay rate of coherently excited excitons in thin quantum wells and microspheres. In this paper we revisit this problem and derive the enhancement factor of the radiative decay due to superradiant effects. In a GaAs quantum well, the excitonic superradiant radiative decay can be roughly 320 times faster than the decay of a free electron-hole pair. The exciton decay rate depends strongly on the lateral size of the wave function when the size is smaller than the inverse of the wave vector of the emitted light. In a GaAs quantum well this corresponds to a distance of 365. Therefore, it is predicted that localization and elastic phonon scattering may lead to decay rates substantially smaller than that predicted for an ideal quantum well. It is also shown that if the quantum well is placed inside a microcavity, the decay rate can be enhanced even further since the cavity modifies the available density of radiation states in a way that matches the superradiant emission. It is predicted that in a matched dielectric cavity the decay rate can be enhanced by an additional factor of 100, but that inhomogeneous broadening may in practice limit the possible enhancement. © 1994 The American Physical Society.

Presentations

• Pau, S. K. (2015, October/Fall). Full Stokes imaging polarimeter. FiO 2015, Oct. 18-22, 2015. San Jose, CA: OSA.
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  invited talk

Reviews

• Balakrishnan, K., & Pau, S. K. (2014. Self-assembled organic optical materials(p. 3). http://www.accessscience.com/content/self-assembled-organic-optical-materials/YB140261.