Adibi, Ali

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Now showing 1 - 10 of 10
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    Multiplex coherent anti-Stokes Raman scattering (MCARS) for chemically sensitive, label-free flow cytometry
    (Georgia Institute of Technology, 2009-12) Camp, Charles Henry, Jr. ; Yegnanarayanan, Siva ; Eftekhar, Ali Asghar ; Sridhar, Hamsa ; Adibi, Ali
    Flow cytometry is an ever-advancing high-throughput multivariate analysis tool that natively provides size and morphological information. To obtain molecular information, however, typically requires the addition of fluorophores, which are limited by spectral overlap, nonspecific binding, available conjugation chemistries, and cellular toxicity. A complementary or alternative, label-free approach to molecular information is through multiplex coherent anti-Stokes Raman scattering (MCARS), which is a coherent, nonlinear optical method that provides a wealth of molecular information by probing the Raman energies within a molecule. In this work, we demonstrate the unique capability of our MCARS flow cytometer to distinguish flowing particles and discuss system performance capabilities and possibilities.
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    Large-scale array of small high-Q microdisk resonators for on-chip spectral analysis
    (Georgia Institute of Technology, 2009-10) Soltani, Mohammad ; Li, Qing ; Yegnanarayanan, Siva ; Momeni, Babak ; Eftekhar, Ali Asghar ; Adibi, Ali
    We demonstrate on-chip, large-scale arrays of small high-Q microdisk resonators, suitable for both in-plane coupling and out-of-plane (imaging) spectral analysis devices with high resolution (linewidth < 50pm to 0.5nm), and large FSR (> 50nm).
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    Analysis of telescope arrays based receiver for deep-space optical communications with Mars
    (Georgia Institute of Technology, 2009-10) Hashmi, A. ; Eftekhar, Ali Asghar ; Adibi, Ali ; Amoozegar, Farid
    Telescope arrays receivers are analyzed for deep-space optical communications between Earth and Mars. It is shown that data rates up to 14 M bits/sec are possible when Mars is at the farthest range from the Earth.
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    Athermal operation in polymer-clad silicon microdisk resonators
    (Georgia Institute of Technology, 2009-10) Alipour, Payam ; Hosseini, Ehsan Shah ; Eftekhar, Ali Asghar ; Momeni, Babak ; Adibi, Ali
    We have used a urethane polymer as cladding to reduce the temperature sensitivity of resonance in high-Q silicon microdisk resonators. A two-order-of-magnitude improvement in resonance stability is demonstrated, and effects on the Q-factor are discussed.
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    High-Q micromechanical resonators in a two-dimensional phononic crystal slab
    (Georgia Institute of Technology, 2009-02) Mohammadi, Saeed ; Eftekhar, Ali Asghar ; Hunt, William D. ; Adibi, Ali
    By creating line defects in the structure of a phononic crystal (PC) made by etching a hexagonal array of holes in a 15 μm thick slab of silicon, high-Q PC resonators are fabricated using a complimentary-metal-oxide-semiconductor-compatible process. The complete phononic band gap of the PC structure supports resonant modes with quality factors of more than 6000 at frequencies as high as 126 MHz. The confinement of acoustic energy is achieved by using only a few PC layers confining the cavity region. The calculated frequencies of resonance of the structure using finite element method are in a very good agreement with the experimental data. The performance of these PC resonator structures makes them excellent candidates for wireless communication and sensing applications.
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    Adaptive Optics based Telescope Arrays Receiver for Compensation of Optical Turbulence Effects in a Deep-Space Optical Communication link with Mars
    (Georgia Institute of Technology, 2009) Hashmi, A. ; Eftekhar, Ali Asghar ; Adibi, Ali ; Amoozegar, Farid
    Future deep-space exploration missions demand a broadband and integrated communication infrastructure to transport the scientific data to Earth. Optical communication employing optical arrays receiver is a viable alternative to the current NASA deep-space RF-based network. Atmospheric turbulence is a major limiting factor for the inter-planetary optical links. Investigation of the use of adaptive optics subsystems is carried out for the compensation of coupled effects of optical turbulence and background noise, in direct detection optical array receivers. The simulation and analysis of an end-toend deep-space optical communication link between a spacecraft in Mars orbit and Earth-based telescope array receivers show that the incorporation of adaptive optics systems results in considerable performance improvement in achievable data rates.
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    Evidence of large high frequency complete phononic band gaps in silicon phononic crystal plates
    (Georgia Institute of Technology, 2008-06-02) Mohammadi, Saeed ; Eftekhar, Ali Asghar ; Khelif, Abdelkrim ; Hunt, William D. ; Adibi, Ali
    We show the evidence of the existence of large complete phononic band gaps (CPBGs) in two-dimensional phononic crystals (PCs) formed by embedding cylindrical air holes in a solid plate (slab). The PC structure is made by etching a hexagonal array of air holes through a freestanding plate of silicon. A fabrication process compatible with metal-oxide-semiconductor technology is used on silicon-on-insulator substrate to realize the PC devices. Measuring the transmission of elastic waves through eight layers of the hexagonal lattice PC in the ΓK direction, more than 30 dB attenuation is observed at a high frequency; i.e., 134 MHz, with a band gap to midgap ratio of 23%. We show that this frequency region matches very well with the expected CPBG found through theoretical calculations.
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    Object localization in the presence of a strong heterogeneous background in fluorescent tomography
    (Georgia Institute of Technology, 2008-06) Mohajerani, Pouyan ; Eftekhar, Ali Asghar ; Adibi, Ali
    We propose a method for object localization in fluorescent tomography (FT) in the presence of a highly heterogeneous background. Existing approaches typically assume a homogeneous background distribution; thus, they are incapable of accurately accounting for the more general case of an unconstrained, possibly heterogeneous, background. The proposed method iteratively solves the inverse problem over a solution space partitioned into a background subspace and an object subspace to simultaneously estimate the background and localize the target fluorescent objects. Simulation results of this algorithm applied to continuous-wave FT demonstrate effective localization of target objects in the presence of highly heterogeneous background distributions.
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    Optimal sparse solution for fluorescent diffuse optical tomography: theory and phantom experimental results
    (Georgia Institute of Technology, 2007-04) Mohajerani, Pouyan ; Eftekhar, Ali Asghar ; Huang, Jiandong ; Adibi, Ali
    We present a method to accurately localize small fluorescent objects within the tissue using fluorescent diffuse optical tomography (FDOT). The proposed method exploits the localized or sparse nature of the fluorophores in the tissue as a priori information to considerably improve the accuracy of the reconstruction of fluorophore distribution. This is accomplished by minimizing a cost function that includes the L₁ norm of the fluorophore distribution vector. Experimental results for a milk-based phantom using a fiber-based cw FDOT system demonstrate the capability of this method in accurately localizing small fluorescent objects deep in the phantom.
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    Effective impedance model for analysis of reflection at the interfaces of photonic crystals
    (Georgia Institute of Technology, 2007-04) Momeni, Babak ; Eftekhar, Ali Asghar ; Adibi, Ali
    We present an alternative definition of impedance to describe the reflection at the interfaces of photonic crystals. We show that this effective impedance can be defined only by the properties of the photonic crystal modes and is independent of the properties of the incident region. This approximate model successfully explains the main features in the reflection spectrum and of various interface terminations of photonic crystals. In particular, we show an impedance matching condition at which reflectionless transmission of power to a low-group-velocity photonic crystal mode is possible, a property that is attractive for various dispersion-based applications of photonic crystals.