Person:
Adibi, Ali

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Publication Search Results

Now showing 1 - 10 of 14
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    Very-high-resolution tandem Fabry-Perot etalon cylindrical beam volume hologram spectrometer for diffuse source spectroscopy
    (Georgia Institute of Technology, 2008-01) Badieirostami, Majid ; Momtahan, Omid ; Hsieh, Chaoray ; Adibi, Ali ; Brady, David J.
    We demonstrate a compact and slitless spectrometer with high resolution formed by cascading a Fabry-Perot etalon (FPE) and a cylindrical beam volume hologram (CBVH). The most significant advantage of this combined spectrometer is that we can independently encode spectral information of a diffuse beam in a 2D plane. Also, we show that in this slitless configuration we can simultaneously benefit from the advantages of both elements: the high resolution of the FPE and the large spectral range of the CBVH. Here, we report on the experimental demonstration of a spectrometer with better than 0.2 nm resolution.
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    Multifunctional and compact spectrometers based on cylindrical beam volume holograms
    (Georgia Institute of Technology, 2007-11) Momtahan, Omid ; Hsieh, Chaoray ; Adibi, Ali
    We propose a new class of slitless spectrometers using cylindrical beam volume holograms. These holograms disperse an input beam in one direction in an output plane while they do not affect the beam in the perpendicular direction. We show that the spectral mapping of the input beam can be obtained in one direction and the beam can be independently modified in the perpendicular direction. Using this unique property, we demonstrate a spectral wrapping technique to considerably increase the operation spectral range of the slitless spectrometers, without sacrificing their resolution.
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    Multiple order coded aperture spectrometer
    (Georgia Institute of Technology, 2007-04) Feller, S. D. ; Chen, Haojun ; Brady, David J. ; Gehm, M. E. ; Hsieh, Chaoray ; Momtahan, Omid ; Adibi, Ali
    We introduce a multiple order coded aperture (MOCA) spectrometer. The MOCA is a system that uses a multiplex hologram and a coded aperture to increase the spectral range and throughput of the system over conventional spectrometers while maintaining spectral resolution. This results in an order of magnitude reduction in system volume with no loss in resolution.
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    Dynamic optical correlation using localized holography
    (Georgia Institute of Technology, 2007-03) Karbaschi, Arash ; Momtahan, Omid ; Adibi, Ali
    A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 μm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.
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    Dispersion multiplexing with broadband filtering for miniature spectrometers
    (Georgia Institute of Technology, 2007-01) Cull, E. C. ; Gehm, M. E. ; Brady, David J. ; Hsieh, Chaoray ; Momtahan, Omid ; Adibi, Ali
    We replace the traditional grating used in a dispersive spectrometer with a multiplex holographic grating to increase the spectral range sensed by the instrument. The multiplexed grating allows us to measure three different, overlapping spectral bands on a color digital focal plane. The detector's broadband color filters, along with a computational inversion algorithm, let us disambiguate measurements made from the three bands. The overlapping spectral bands allow us to measure a greater spectral bandwidth than a traditional spectrometer with the same sized detector. Additionally, our spectrometer uses a static coded aperture mask in the place of a slit. The aperture mask allows increased light throughput, offsetting the photon loss at the broadband filters. We present our proof-of-concept dispersion multiplexing spectrometer design with experimental measurements to verify its operation.
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    Simple and efficient software-based stabilized holographic recording system
    (Georgia Institute of Technology, 2006-12) Cadena, George H. ; Momtahan, Omid ; Adibi, Ali
    A simple, inexpensive, and efficient stabilized holographic recording setup is described which precludes the destructive fringe movement encountered in long-lasting holographic exposures. Utilizing a straightforward methodology, stability greater than ƛ/25 (recording wavelength ƛ=532 nm) for holographic recording sessions longer than 6 h can be achieved. Due to the software basis of this design, in the LabVIEW platform, the functionality of expensive hardware components is provided in software. Moreover, this setup is modularly designed and can be easily replicated for multiple labs, with the need only of the following hardware components: a piezo-shifting mirror, a computer, a data-acquisition card, and a photodetector.
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    Analysis of slitless holographic spectrometers implemented by spherical beam volume holograms
    (Georgia Institute of Technology, 2006-05) Momtahan, Omid ; Hsieh, Chaoray ; Adibi, Ali ; Brady, David J.
    The analysis of a slitless volume holographic spectrometer is presented in detail. The spectrometer is based on a spherical beam volume hologram followed by a Fourier-transforming lens and a CCD. It is shown that the spectrometer is not sensitive to the incident angle of the input beam for the practical range of applications. A holographic spectrometer based on the conventional implementation is also analyzed, and the results are used to compare the performance of the proposed method with the conventional one. The experimental results are consistent with the theoretical study. It is also shown that the slitless volume holographic spectrometer lumps three elements (the entrance slit, the collimator, and the diffractive element) of the conventional spectrometer into one spherical beam volume hologram. Based on the unique features of the slitless volume holographic spectrometer, we believe it is a good candidate for portable spectroscopy for environmental and biological applications.
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    Sensitivity variation in two-center holographic recording
    (Georgia Institute of Technology, 2005-10) Momtahan, Omid ; Cadena, George H. ; Adibi, Ali
    An experimental study of variation of sensitivity with recording and sensitizing intensities in two-center recording is presented. The experimental results are in good agreement with the theoretical predictions. It is shown experimentally, for what is to our knowledge the first time, that the sensitivity is a function of the ratio of recording to sensitizing intensities and not the absolute intensities. Also, the ratio of recording to sensitizing intensities should be small to obtain high sensitivity values. We also report the highest sensitivity (S=0.15 cm/J) that has been achieved to date for a LiNbO₃:Fe:Mn crystal
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    Optical correlation using gated localized holography
    (Georgia Institute of Technology, 2005-08) Karbaschi, Arash ; Momtahan, Omid ; Adibi, Ali ; Javidi, Bahram
    We present a new technique for optical correlation using gated holographic recording by which the holograms are localized in separate slices along the recording medium. We compare the performance of localized holographic correlators (LHCs) with that of the conventional correlators using normal volume holography. Crosstalk, shift invariance, and the capacities of the LHC and of the conventional method are examined. We show that the proposed method has better performance and distinctive advantages over the conventional method. These advantages include selective recording and erasure for dynamic pattern modification, extendable capacity, and compactness.
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    Compact Fourier-transform volume holographic spectrometer for diffuse source spectroscopy
    (Georgia Institute of Technology, 2005-04) Hsieh, Chaoray ; Momtahan, Omid ; Karbaschi, Arash ; Adibi, Ali
    We present a new idea for diffuse source spectroscopy using a Fourier-transform volume holographic spectrometer formed by a Fourier-transform lens, a volume hologram, and a CCD. We show that this spectrometer can operate well under spatially incoherent light illumination. Furthermore, this spectrometer is less bulky, less sensitive to input alignment, and potentially more appropriate for implementation of highly sensitive spectrometers than conventional spectrometers.