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Papers by Islam Ashry
Optics express, Jan 25, 2014
We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...
Ultrafast Imaging and Spectroscopy, 2013
ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cann... more ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cannot possess significant secondorder nonlinearity. We recently developed a method that can potentially overcome this deficiency by coating a silica fiber taper with layers of radially aligned nonlinear molecules. The coating process can be accomplished through layerby- layer self-assembly, where the alignment of the nonlinear molecules is maintained through electrostatic interaction. As a result, the nonlinear fiber structures are thermodynamically stable and can generate significant second-order nonlinear responses despite their full rotational symmetry. This prediction has been experimentally confirmed through SHG measurements. To further enhance the overall second-order nonlinearity, we have developed an UV-ablation-based approach that can generate second-order nonlinearity that is spatially periodic along the fiber taper. Our preliminary experiments suggest that SHG intensity can be enhanced by such quasi-phase-matching configurations. We can also use the self-assembly approach to construct tunable plasmonic systems. As a proof-of-concept study, we assembled swellable polymer films over a planar Au substrate through layer-by-layer assembly and covered the swellable polymer with a monolayer of quantum dots. After immersing the swellable plasmonic structure in solution and adjusting its pH value, we used a fluorescence lifetime based approach to demonstrate that the thickness of the swellable polymers can be modified by almost 400%. The fluorescence lifetime measurements also confirmed that the plasmonic resonance can be significantly modified by the swellable polymers.
Lecture Notes in Electrical Engineering, 2014
A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer ha... more A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer has the ability to provide variable delay times and can store the contenting packets for a relatively long time.
Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014
Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014
Journal of Nanophotonics, 2016
Applied Optics, 2015
Plasmonics-based polarizers are important for many photonic devices and applications. In this pap... more Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.
Nanoengineering: Fabrication, Properties, Optics, and Devices XII, 2015
Optics express, Jan 25, 2014
We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...
Optics express, Jan 25, 2014
We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...
Ultrafast Imaging and Spectroscopy, 2013
ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cann... more ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cannot possess significant secondorder nonlinearity. We recently developed a method that can potentially overcome this deficiency by coating a silica fiber taper with layers of radially aligned nonlinear molecules. The coating process can be accomplished through layerby- layer self-assembly, where the alignment of the nonlinear molecules is maintained through electrostatic interaction. As a result, the nonlinear fiber structures are thermodynamically stable and can generate significant second-order nonlinear responses despite their full rotational symmetry. This prediction has been experimentally confirmed through SHG measurements. To further enhance the overall second-order nonlinearity, we have developed an UV-ablation-based approach that can generate second-order nonlinearity that is spatially periodic along the fiber taper. Our preliminary experiments suggest that SHG intensity can be enhanced by such quasi-phase-matching configurations. We can also use the self-assembly approach to construct tunable plasmonic systems. As a proof-of-concept study, we assembled swellable polymer films over a planar Au substrate through layer-by-layer assembly and covered the swellable polymer with a monolayer of quantum dots. After immersing the swellable plasmonic structure in solution and adjusting its pH value, we used a fluorescence lifetime based approach to demonstrate that the thickness of the swellable polymers can be modified by almost 400%. The fluorescence lifetime measurements also confirmed that the plasmonic resonance can be significantly modified by the swellable polymers.
Lecture Notes in Electrical Engineering, 2014
A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer ha... more A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer has the ability to provide variable delay times and can store the contenting packets for a relatively long time.
Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014
Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014
Journal of Nanophotonics, 2016
Applied Optics, 2015
Plasmonics-based polarizers are important for many photonic devices and applications. In this pap... more Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.
Nanoengineering: Fabrication, Properties, Optics, and Devices XII, 2015
Optics express, Jan 25, 2014
We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...