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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Ultraslow optical modes in Bose-Einstein condensates(Society of Photo-optical Instrumentation Engineers (SPIE), 2007) Tarhan, Devrim; Postacıoğlu, Nazmi; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674Light can be slowed down to ultraslow speeds via electromagnetically induced transparency in atomic Bose-Einstein condensates. This is thought to be useful for storage of quantum information for weak probe pulses. We investigate the effects of inhomogeneous density profile of-the condensate on propagation of such ultraslow pulses. We find that spatial density of an atomic condensate leads to a graded refractive index profile, for an off-resonant probe pulse when condensate parameters are suitably chosen. Within the window of negligible absorption, conditions for degenerate multiple waveguide modes are determined. Both analytical and numerical studies are presented to reveal the effects of experimentally controllable parameters, such as temperature and interatomic interaction strength on the number of modes. Group velocity dispersion and modal dispersion are discussed. The effect of waveguide dispersion, in addition to usual material dispersion, on ultraslow pulses is pointed out.Publication Open Access Observation of two-photon interference using the zero-phonon-line emission of a single molecule(Institute of Physics (IOP) Publishing, 2006) Ehrl, M.; Hellerer, Th.; Brauchle, C.; Zumbusch, A.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Kiraz, Alper; Faculty Member; Faculty Member; Department of Physics; College of Sciences; 1674; 22542We report the results of coincidence counting experiments at the output of a Michelson interferometer using the zero-phonon-line emission of a single molecule at 1.4 K. Under continuous wave excitation, we observe the absence of coincidence counts as an indication of two-photon interference. This corresponds to the observation of Hong-Ou-Mandel correlations.Publication Open Access Quantum state transfer among crystallographic groups of N-V centers in diamond(Society of Photo-optical Instrumentation Engineers (SPIE), 2011) Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We investigate collections of Nitrogen-Vacancy (N-V) Centers in diamond crystals coupled to a circuit QED system of a coplanar waveguide (CPWG) resonator. Our analysis reveals that different symmetry axes oriented N-V centers in the diamond host can be grouped into bosonic modes of collective quasi-spin wave excitations so that the hybrid system can be described as an analog of an exciton-polariton type cavity QED model. We examine such model for quantum state transfer among distinct crystallographic groups of N-V centers in a single diamond as well as two spatially distant diamonds. Rabi oscillations, mode entanglement, possible use of N-V classes as spin ensemble qubits and an implementation of continuous-time quantum random walk are discussed.Publication Open Access Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling(American Physical Society (APS), 2013) Subaşı, Ahmet Levent; Department of Physics; Işkın, Menderes; Faculty Member; Department of Physics; College of Sciences; 29659We analyze the effects of in-and out-of-plane Zeeman fields on the BCS-Bose-Einstein condensation (BEC) evolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit coupling (SOC). We show that the ground state of the system involves gapless superfluid phases that can be distinguished with respect to the topology of the momentum-space regions with zero excitation energy. For the BCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros may correspond to one or two doubly degenerate spheres, two or four spheres, two or four concave spheroids, or one or two doubly degenerate circles, depending on the combination of Zeeman fields and SOC. Such changes in the topology signal a quantum phase transition between distinct superfluid phases and leave their signatures on some thermodynamic quantities. We also analyze the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform superfluid phases with finite center-of-mass momentum and obtain an even richer phase diagram.Publication Open Access Silicon photonics with microspheres(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Department of Physics; N/A; Serpengüzel, Ali; Akatlar, Onur; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; College of Sciences; College of Engineering; 27855; N/A; 194455Silicon microspheres coupled to optical fibers have been used for optical channel dropping in the near-IR. The observed morphology dependent resonances had quality factors of 100000. These optical resonances provide the necessary narrow linewidths, that are needed for high resolution optical filtering applications in the near-IR. In addition to filtering, detection, and switching applications of this photonic system is studied in the near-IR as well as far-IR. The silicon microsphere shows promise as a building block for silicon photonics in the near-IR as well as, mid-IR, and far-IR.Publication Open Access Dynamical properties of a coupled nonlinear dielectric waveguide-surface-plasmon system as another type of Josephson junction(Society of Photo-optical Instrumentation Engineers (SPIE), 2011) Department of Physics; Özok, Yasa Ekşioğlu; Müstecaplıoğlu, Özgür Esat; Güven, Kaan; Faculty Member; Faculty Member; Department of Physics; College of Sciences; N/A; 1674; 52290We demonstrate that a weakly-coupled nonlinear dielectric waveguide surface-plasmon (DWSP-JJ) system can be formulated in analogy to bosonic Josephson junction of atomic condensates at very low temperatures, yet it exhibits different dynamical features. Such a system can be realized along a metal - dielectric interface where the dielectric medium hosts a nonlinear waveguide (e. g. fiber) for soliton propagation. The inherently dynamic coupling parameter generates novel features in the phase space.Publication Open Access Augmented reality 3d display using head-mounted projectors and transparent retro-reflective screen(Society of Photo-optical Instrumentation Engineers (SPIE), 2017) Department of Electrical and Electronics Engineering; Soomro, Shoaib Rehman; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579A 3D augmented reality display is proposed that can provide glass-free stereo parallax using a highly transparent projection screen. The proposed display is based on a transparent retro-reflective screen and a pair of laser pico projectors placed close to the viewer's head. The retro-reflective screen directs incident light towards its source with little scattering so that each of the viewer's eyes only perceives the content projected by the associated projector. Each projector displays one of the two components (left or right channel) of stereo content. The retro-reflective nature of screen provides high brightness compared to the regular diffused screens. The partially patterned retro-reflective material on clear substrate introduces optical transparency and facilitates the viewer to see the real-world scene on the other side of screen. The working principle and design of the proposed see-through 3D display are presented. A tabletop prototype consisting of an in-house fabricated 60x40cm(2) see-through retro-reflective screen and a pair of 30 lumen pico-projectors with custom 3D printed housings is demonstrated. Geometric calibration between projectors and optimal viewing conditions (eye box size, eye-to-projector distance) are discussed. The display performance is evaluated by measuring the brightness and crosstalk for each eye. The screen provides high brightness (up to 300 cd/ m2 per eye) using 30 lumens mobile projectors while maintaining the 75% screen transparency. The crosstalk between left and right views is measured as < 10% at the optimum distance of 125-175 cm, which is within acceptable range.Publication Open Access Dynamic characterization and damping control of a MEMS structure - art. no. 671509(Society of Photo-optical Instrumentation Engineers (SPIE), 2007) Department of Mechanical Engineering; Alaca, Ilgım Veryeri; Başdoğan, İpek; Faculty Member; Department of Mechanical Engineering; College of Engineering; 50569; 179940Publication Open Access Dynamic accommodation measurement using Purkinje reflections and ML algorithms(Society of Photo-optical Instrumentation Engineers (SPIE), 2023) Department of Electrical and Electronics Engineering; N/A; Aygün, Uğur; Şahin, Afsun; Ürey, Hakan; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; School of Medicine; N/A; N/A; N/A; 171267; 8579We developed a prototype device for dynamic gaze and accommodation measurements based on 4 Purkinje reflections (PR) suitable for use in AR and ophthalmology applications. PR1&2 and PR3&4 are used for accurate gaze and accommodation measurements, respectively. Our eye-model was developed in Zemax and matches the experiments well. Our model predicts the accommodation from 25cm to infinity (<4 diopters) with better than 0,25D accuracy. We performed repeatability tests and obtained accurate gaze and accommodation estimations using 15 subjects. We are generating a large synthetic data set using physically accurate models and machine learning algorithms.Publication Open Access Wavelength selection in measuring red blood cell aggregation based on light transmittance(Society of Photo-optical Instrumentation Engineers (SPIE), 2011) Uyuklu, Mehmet; Canpolat, Murat; Meiselman, Herbert J.; N/A; Başkurt, Oğuz Kerim; Faculty Member; School of Medicine; 2389The reversible aggregation of red blood cells (RBC) is of current basic science and clinical interest. Using a flow channel and light transmittance (LT) through RBC suspensions, we have examined the effects of wavelength (500 to 900 nm) on the static and dynamic aspects of RBC aggregation for normal blood and suspensions with reduced or enhanced aggregation; the effects of oxygenation were also explored. Salient observations include: 1. significant effects of wavelength on aggregation parameters reflecting the extent of aggregation (i.e., number of RBC per aggregate); 2. no significant effects of wavelength on parameters reflecting the time course of RBC aggregation; 3. a prominent influence of hemoglobin oxygen saturation on both extent and time-course related aggregation parameters measured at wavelengths less than 700 nm, but only on the time-course at 800 nm; and 4. the power of parameters in detecting a given alteration of RBC aggregation is affected by wavelength, in general being greater at higher wavelengths. It is recommended that light sources with wavelengths around 800 nm be used in instruments for measuring RBC aggregation via LT.