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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3

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Department: search.filters.department.Department of PhysicsSubject: search.filters.subject.Applied physics

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Now showing 1 - 10 of 27
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    Survival probability in a quantum walk on a one-dimensional lattice with partially absorbing traps
    (American Scientific Publishers, 2013) Gonulol, Meltem; Aydiner, Ekrem; Shikano, Yutaka; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674
    Time dependence of the survival probability in a one dimensional lattice with randomly distributed and partial absorbing traps is analyzed as a function of concentration and absorption probability of the traps. The short and long time behaviors of the non-interacting quantum walks are identified with stretched exponentials. Dynamical scaling laws of the short and long time regimes as well as the crossover time between them are characterized. It is found that the short time behavior is more sensitive to the absorption probability and the crossover takes longer time for more transparent traps. Moreover, the stretching exponents increase with the transparency of the traps.
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    Vortex lattice of a Bose-Einstein condensate as a photonic band gap material
    (Institute of Physics (IOP) Publishing, 2009) Tasgin, M. E.; Oktel, M. O.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674
    Photonic crystal behavior of a rotating Bose-Einstein condensate with a triangular vortex lattice is reviewed and a scheme for getting much wider band gaps is proposed. It is shown that photonic band gaps can be widened an order of magnitude more by using a Raman scheme of index enhancement, in comparison to previously considered upper level microwave scheme.
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    Influence of doping concentration on the power performance of diode-pumped continuous-wave Tm 3+:YAlO 3 lasers
    (IEEE-Inst Electrical Electronics Engineers Inc, 2005) N/A; N/A; Department of Physics; Department of Physics; Kalaycıoğlu, Hamit; Sennaroğlu, Alphan; Kurt, Adnan; PhD Student; Faculty Member; Teaching Faculty; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 23851; 194455
    We investigated the effect of thulium ion concentration on the continuous-wave (CW) power performance of diode single-end-pumped thulium-doped YAlO3 (Tm:YAP) lasers. Three samples with 1.5%, 3%, and 4% Tm3+ concentration were examined at 18 ◦C. Lifetime and fluorescence measurements were further performed to assess the strength of cross relaxation and nonradiative decay. Our results showed that in single-end-pumped configurations, the best CW power performance was obtained with the 1.5% Tm:YAP sample, and laser performance of the samples degraded monotonically with increasing Tm3+ concentration. By using 9.5 W of incident pump power at 797 nm, a maximum of 1430 mW of output power was obtained with the 1.5% Tm:YAP sample and 2% output coupler. We discuss how the effects of cross relaxation, reabsorption, nonradiative decay, and internal heating vary with increasing concentration. Spectroscopic measurements and rate-equation analysis suggest that cross relaxation should already be effective in samples with 1.5% Tm3+ ion concentration and doping concentrations larger than 4% will lead to degradation in power performance due to higher nonradiative decay rates and larger reabsorption losses.
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    Optofluidic FRET microlasers based on surfacesupported liquid microdroplets
    (Iop Publishing Ltd, 2014) Jonas, A.; N/A; N/A; Department of Physics; Özelci, Ersan; Aas, Mehdi; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 22542
    We demonstrate optofluidic microlasers using highly efficient non-radiative Forster resonance energy transfer (FRET) for pumping of gain medium placed within liquid microdroplets situated on a superhydrophobic surface. Microdroplets generated from a mixture of ethylene glycol, glycerol, and water and stained with the FRET donor-acceptor dye pair Rhodamine 6G-Rhodamine 700 serve as active optical resonant cavities hosting high-quality whispering gallery modes. Upon direct optical pumping of the donor with a pulsed laser, lasing is observed in the emission band of the acceptor as a result of efficient FRET coupling between the acceptor and donor molecules. FRET lasing is characterized for different acceptor and donor concentrations, and threshold pump fluences of acceptor lasing as low as 6.3 mJ cm(-2) are demonstrated. We also verify the dominance of the non-radiative FRET over cavity-assisted radiative energy transfer for the range of parameters studied in the experiments.
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    Symmetric meandering distributed feedback structures for silicon photonic circuits
    (Ieee-Inst Electrical Electronics Engineers Inc, 2020) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Physics; Chaudhry, Muhammad Rehan; Zakwan, Muhammad; Onbaşlı, Mehmet Cengiz; Serpengüzel, Ali; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; N/A; 258783; 27855
    Fano lineshapes and electro-magnetically induced transparency-like peaks in the transmittance of a transverse electric polarization silicon-on-insulator symmetric meandering distributed feedback photonic structure are demonstrated. The coupling constants at the five identical directional couplers are varied to obtain the desired spectral responses. The numerically simulated and experimentally measured transmittance spectra are in good agreement with each other. The numerically calculated and experimentally measured insertion loss for the symmetric meandering distributed feedback structure with directional coupler coupling length L-c = 10 mu m are respectively -5 dB and -17 dB, including the grating couplers. Fano lineshapes with mode splitting is observed at directional coupler coupling constant value C of 0.24. For coupling constant value of C similar to 0.78, electro-magnetically induced transparency-like peaks are observed, and spectrally adjusted by varying the directional coupler coupling length. Fano lineshapes show an extinction ratio of more than 26 dB and slope ratio of 368 dB/nm. Electro-magnetically induced transparency-like peaks show a quality-factor on the order of 5 x 10(4). The symmetric meandering distributed feedback structure shows promise for possible applications as an optical switch, and an optical filter in wavelength division multiplexing and data networks, as well as optical sensors in optical diagnostics, using silicon photonics.
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    Bulk Nd³+ -doped tellurite glass laser at 1.37 μm
    (Springer, 2010) N/A; Department of Physics; Çankaya, Hüseyin; Sennaroğlu, Alphan; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851
    We have demonstrated, for the first time to our knowledge, lasing at 1.37 mu m in a tellurite-based glass host doped with 0.5 mol.% neodymium: Nd3+:(0.8)TeO2-(0.2)WO3. The gain-switched laser could be operated with 59 mu J threshold pulse energy as well as 5.5% slope efficiency. As high as 6 mu J-pulses with a duration of 1.74 mu s were obtained. The pulse repetition rate was 1 kHz. The emission cross section from the threshold analysis turned out to be 1.57x10(-20) cm(2) at 1370 nm by taking into account excited-state absorption from F-4(3/2) to (4)G(7/2) energy level. Furthermore, the ratio of excited-state absorption to the emission cross section was found out to be 0.78 by using the slope efficiency value.
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    Comparison of the NMR and neutron scattering experiments on cuprates with nonmagnetic impurities
    (World Scientific Publ Co Pte Ltd, 2000) Department of Physics; Department of Physics; Bulut, Nejat; Yaz, Ümit; Faculty Member; Undergraduate Student; Department of Physics; College of Sciences; College of Sciences; 4963; N/A
    The NMR and neutron scattering experiments on YBa2Cu3O7 with U and Zn impurities are compared using a simple framework exhibiting short-range antiferomagnetic correlations. The model parameters are determined by fitting the NMR rate T-2(-1) of the pure system, and the effective impurity potential is approximated by a static extended form. The results of the calculations are compared with the experimental data, and their implications are discussed.
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    Aerogels for optofluidic waveguides
    (MDPI, 2017) Jonas, Alexandr; N/A; Department of Physics; Department of Chemical and Biological Engineering; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 29633; 22542
    Aerogels-solid materials keeping their internal structure of interconnected submicron-sized pores intact upon exchanging the pore liquid with a gas-were first synthesized in 1932 by Samuel Kistler. Overall, an aerogel is a special form of a highly porous material with a very low solid density and it is composed of individual nano-sized particles or fibers that are connected to form a three-dimensional network. The unique properties of these materials, such as open pores and high surface areas, are attributed to their high porosity and irregular solid structure, which can be tuned through proper selection of the preparation conditions. Moreover, their low refractive index makes them a remarkable solid-cladding material for developing liquid-core optofluidic waveguides based on total internal reflection of light. This paper is a comprehensive review of the literature on the use of aerogels for optofluidic waveguide applications. First, an overview of different types of aerogels and their physicochemical properties is presented. Subsequently, possible techniques to fabricate channels in aerogel monoliths are discussed and methods to make the channel surfaces hydrophobic are described in detail. Studies in the literature on the characterization of light propagation in liquid-filled channels within aerogel monoliths as well as their light-guiding characteristics are discussed. Finally, possible applications of aerogel-based optofluidic waveguides are described.
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    Miniature droplet-based FRET lasers stabilized by superhydrophobic surfaces
    (IEEE, 2014) Jonas, A.; N/A; N/A; Department of Physics; Özelci, Ersan; Aas, Mehdi; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 22542
    We demonstrate optofluidic microlasers based on liquid microdroplets stabilized by a superhydrophobic surface. Lasing is achieved using highly efficient non-radiative Forster resonance energy transfer between donor and acceptor molecules placed within the droplets.
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    Strain modulated band gaps of semiconducting zigzag single walled carbon nanotubes
    (Natl Inst Optoelectronics, 2015) Eyecioğlu, Önder.; Mısırlıoğlu, Banu Süngü; Department of Physics; Dereli, Gülay; Other; Department of Physics; College of Sciences; N/A
    Strain can alter the electronic properties of materials. At the nanoscale, small displacements of atoms could have large effects. In this study, we have examined how elastic strain can modify the energy band gaps of semiconducting zigzag Single Walled Carbon Nanotubes (SWCNTs). The electronic structure of SWCNTs have been computed for each deformed configurations by means of real space, Order(N) Tight Binding Molecular Dynamic (O(N) TBMD) simulations. During the applications of uniaxial strain, carbon atoms are moved slightly from their equilibrium positions, but their atomic bonds are not broken. Three different kinds of semiconducting zigzag SWCNTs are chosen. (12,0) SWCNT, although a semiconducting SWCNT, is quasi-metallic in its pristine state. Application of stretching and compression opens its band gap. Thus under strain (12,0) SWCNT shows metallic-semiconducting transitions. (13,0) and (14,0) zigzag SWCNTs are semiconductors having energy band gap values of 0.44eV and 0.55eV in their pristine state. The energy band gap of (13,0) SWCNT decreases with increasing absolute value of compression. On the other hand, the energy band gap of (14,0) SWCNT decreases with increasing value of tension. So in both cases, the energy band gap closes and semiconducting metallic transitions are observed. Flexibilities of the stretched hexagonal network of SWCNTs are displayed in terms of carbon-carbon bond-lengths, bond-angles and radial distribution functions. Correlations between the strain induced structural changes and the electronic properties of SWCNTs are discussed.