Department of Physics
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Browsing Department of Physics by Department "Electrical and Computer Engineering"
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- Analysis of optical response of long period fiber gratings to nm-thick thin-film coatingsWang, Zhiyong; Heflin, James R.; Stolen, Rogers H.; Ramachandran, Siddharth (Optical Society of America, 2005-04-01)We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thickthin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance index-modulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thin-film coating. (C) 2005 Optical Society of America.
- Demonstration Of A Cylindrically Symmetric Second-Order Nonlinear Fiber with Self-Assembled Organic Surface LayersDaengngam, Chalongrat; Hofmann, M.; Liu, Z. W.; Wang, Anbo; Heflin, James R.; Xu, Yong (Optical Society of America, 2011-05-01)We report the fabrication and characterization of a cylindrically symmetric fiber structure that possesses significant and thermodynamically stable second-order nonlinearity. Such fiber structure is produced through nanoscale self-assembly of nonlinear molecules on a silica fiber taper and possesses full rotational symmetry. Despite its highly symmetric configuration, we observed significant second harmonic generation (SHG) and obtained good agreement between experimental results and theoretical predictions. (C) 2011 Optical Society of America
- Estimate Of The Incoherent-Scattering Contribution To Lidar Backscatter From Cloudsde Wolf, D. A.; Russchenberg, H. W. J.; Lighthart, L. P. (Optical Society of America, 1999-09-01)Lidar backscatter from clouds in the Delft University of Technology experiment is complicated by the fact that the transmitter has a narrow beam width, whereas the receiver has a much wider one. The issue here is whether reception of light scattered incoherently by cloud particles can contribute appreciably to the received power. The incoherent contribution can come from within as well as from outside the transmitter beam but in any case is due to at least two scattering processes in the cloud that are not included in the coherent forward scatter that leads to the usual exponentially attenuated contribution from single-particle backscatter. It is conceivable that a sizable fraction of the total received power within the receiver beam width is due to such incoherent-scattering processes. The ratio of this contribution to the direct (but attenuated) reflection from a single particle is estimated here by means of a distorted-Born approximation to the wave equation (with an incident cw monochromatic wave) and by comparison of the magnitude of the doubly scattered to that of the singly scattered flux. The same expressions are also obtained from a radiative-transfer formalism. The ratio underestimates incoherent multiple scattering when it is not small. Corrections that are due to changes in polarization are noted. (C) 1999 Optical Society of America.
- High quality factor silica microspheres functionalized with self-assembled nanomaterialsKandas, Ishac L. N.; Zhang, Baigang; Daengngam, Chalongrat; Ashry, Islam; Jao, Chih-Yu; Peng, Bo; Ozdemir, Sahin K.; Robinson, Hans D.; Heflin, James R.; Yang, Lan; Xu, Yong (Optical Society of America, 2013-09-01)With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e. g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement. (C) 2013 Optical Society of America
- Highly sensitive optical response of optical fiber long period gratings to nanometer-thick ionic self-assembled multilayersWang, Zhiyong; Heflin, James R.; Stolen, Rogers H.; Ramachandran, Siddharth (AIP Publishing, 2005-05-01)Ionic self-assembled multilayers deposited on long period fiber gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Fine control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition technique for fine-tuning grating properties. In addition a variety of biological and chemical sensing agents can easily be incorporated into these films, which makes this an attractive platform for realization of high-performance LPG-based sensors. (c) 2005 American Institute of Physics.
- Incoherent Bandpass Spatial-Filtering with Longitudinal PeriodicityPoon, Ting-Chung; Indebetouw, Guy J. (Optical Society of America, 1990-09-01)We explore the possibility of realizing bandpass filtering with longitudinal periodicity in incoherent systems. The necessary condition for spatial filtering to be longitudinally periodic is derived. Results indicate that bandpass filtering with longitudinal periodicity can be achieved in a two-pupil system with Fresnel zone plates with a small opening ratio as the pupils.
- Incoherent Spatial-Filtering with A Scanning Heterodyne SystemIndebetouw, Guy J.; Poon, Ting-Chung (Optical Society of America, 1984-01-01)Imaging systems with two pupils in the receiving optics have been used to synthesize bipolar point spread functions in incoherent image processing. We describe a two-pupil system using a scanning illumination technique and compare its attributes with more conventional techniques. Experimental examples using two-pupil interaction and an acoustooptic frequency offset for the direct 2-D bandpass filtering of diffusely reflecting objects are presented.
- Interferometric Model For Phase Analysis in Fiber CouplersFang, Xiaojun; Claus, Richard O.; Indebetouw, Guy J. (Optical Society of America, 1996-07-01)An interferometric model is proposed to estimate the phase differences in lossless, strongly coupled biconical fiber couplers. This approximate method is simpler than the traditional s-parameter network theory-based analysis technique and minimizes the number of unknowns. The phase difference between the transmitted and coupled light fields is directly related to the field interaction and can be estimated by employing the energy conservation and mode orthogonality principles. The maximum coupling coefficient and dependence of phase difference on coupling conditions can be analyzed for multiport single-mode fiber couplers. (C) 1996 Optical Society of America
- Irreversible adsorption of gold nanospheres on fiber optical tapers and microspheresYi, Jihaeng; Jao, Chih-Yu; Kandas, Ishac L. N.; Liu, Bo; Xu, Yong; Robinson, Hans D. (AIP Publishing, 2012-04-01)We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701730]
- Proposal and analysis of a silica fiber with large and thermodynamically stable second order nonlinearityXu, Yong; Wang, Anbo; Heflin, James R.; Liu, Z. W. (AIP Publishing, 2007-05-01)The authors propose a general approach that can produce a silica fiber with large and thermodynamically stable second order nonlinearity. They estimate that it is possible to achieve second harmonic generation efficiency of more than 10% in such a nonlinear fiber with a length of a few hundred microns. By maintaining a high degree of spatial symmetry, the proposed nonlinear fiber can naturally generate polarization entangled photon pairs, a physical object of enormous significance for quantum information technology. (c) 2007 American Institute of Physics.
- Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acidDickerson, B. D.; Irving, D. M.; Herz, E.; Claus, Richard O.; Spillman, William B. Jr.; Meissner, K. E. (AIP Publishing, 2005-04-01)A diffusion-barrier model described the early evolution of size-dependent photoluminescence emission from CdSe quantum dots formed by organometallic synthesis. Emission peak widths, emission redshift rates, and nanocrystal growth rates all decreased to a minimum at a reaction completion time. Growth after the completion time by Ostwald ripening was marked by a doubling of the activation energy. The temperature dependence of both reaction completion rates and photoluminescence redshift rates followed Arrhenius behavior governed by activation energies that increased with solvent molecular weight, in this limited case. In stearic acid and in trioctylphosphine oxide, the typical activation energies were 0.6 +/- 0.1 and 0.92 +/- 0.26 eV/molecule, respectively. (c) 2005 American Institute of Physics.
- Thickness dependence of second-harmonic generation in thin films fabricated from ionically self-assembled monolayersHeflin, James R.; Figura, C.; Marciu, D.; Liu, Y.; Claus, Richard O. (AIP Publishing, 1999-01-01)An ionically self-assembled monolayer (ISAM) technique for thin-film deposition has been employed to fabricate materials possessing the noncentrosymmetry that is requisite for a second-order, chi((2)), nonlinear optical response. As a result of the ionic attraction between successive layers, the ISAM chi((2)) films self-assemble into a noncentrosymmetric structure that has exhibited no measurable decay of chi((2)) at room temperature over a period of more than one year. The second-harmonic intensity of the films exhibits the expected quadratic dependence on film thickness up to at least 100 bilayers, corresponding to a film thickness of 120 nm. The polarization dependence of the second-harmonic generation yields a value of 35 degrees for the average tilt angle of the nonlinear optical chromophores away from the surface normal. (C) 1999 American Institute of Physics; [S0003-6951(99)02904-6].
- Three-Dimensional Microscopy And Sectional Image Reconstruction Using Optical Scanning HolographyLam, Edmund Y.; Zhang, Xin; Vo, Huy; Poon, Ting-Chung; Indebetouw, Guy J. (Optical Society of America, 2009-08-01)Fast acquisition and high axial resolution are two primary requirements for three-dimensional microscopy. However, they are sometimes conflicting: imaging modalities such as confocal imaging can deliver superior resolution at the expense of sequential acquisition at different axial planes, which is a time-consuming process. Optical scanning holography (OSH) promises to deliver a good trade-off between these two goals. With just a single scan, we can capture the entire three-dimensional volume in a digital hologram; the data can then be processed to obtain the individual sections. An accurate modeling of the imaging system is key to devising an appropriate image reconstruction algorithm, especially for real data where random noise and other imaging imperfections must be taken into account. In this paper we demonstrate sectional image reconstruction by applying an inverse imaging sectioning technique to experimental OSH data of biological specimens and visualizing the sections using the OSA Interactive Science Publishing software. (C) 2009 Optical Society of America
- Three-Dimensional Point Spread Functions Of an Optical Heterodyne Scanning Image ProcessorPoon, Ting-Chung; Indebetouw, Guy J. (Optical Society of America, 2003-10-01)We study the three-dimensional (3-D) imaging properties of an optical heterodyne scanning image processor. The image processor is a two-pupil optical system capable of 3-D imaging coherently or incoherently, depending on the detection scheme used. We derive the imaging properties in terms of the two pupils and then show an important 3-D imaging application in scanning holography by deriving its 3-D point spread functions and compare them with conventional 3-D imaging systems. (C) 2003 Optical Society of America.
- Transient pulses from exploding primordial black holes as a signature of an extra dimensionKavic, Michael; Simonetti, John H.; Cutchin, Sean E.; Ellingson, Steven W.; Patterson, Cameron D. (IOP, 2008-11-01)An evaporating black hole in the presence of an extra spatial dimension would undergo an explosive phase of evaporation. We show that such an event, involving a primordial black hole, can produce a detectable, distinguishable electromagnetic pulse, signaling the existence of an extra dimension of size L ∼ 10−18 − 10−20 m. We derive a generic relationship between the Lorentz factor of a pulse-producing “fireball” and the TeV energy scale. For an ordinary toroidally compactified extra dimension, transient radio-pulse searches probe the electroweak energy scale (∼0.1 TeV), enabling comparison with the Large Hadron Collider.
- Two-Dimensional Textural Edge Detection Using Ω-Gaussian FilterPark, Jinwoo; Poon, Ting-Chung; Indebetouw, Guy J. (Optical Society of America, 1986-11-01)A textural edge detection frequency domain filter is proposed to locate the boundary between two textural domains modulated by different spatial frequencies. This filter is derived from a zero-order prolate spheroidal function which can be approximated by a _-Gaussian shape. The extension to a 2-D rotational symmetric filter capable of locating textural edges independently of the relative orientation of the textural frequencies is demonstrated. Results show that the proposed filter is more effective at concentrating the output energy around the edge than the filter proposed by Shanmugan et al., which was derived with an additional constraint of evenness in the design of the filter function.