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Publication Open Access A MEMS based visible-NIR Fourier transform microspectrometer - art. no. 61860C(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Wolter, A.; Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; Işıkman, Serhan Ömer; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579; N/ADesign, fabrication and characterization of a novel out-of-plane vertical comb-drive actuator based Fourier transform microspectrometer (FTS) is presented. The spectrometer utilizes resonant mode vertical comb actuators as a variable-depth diffraction grating and a single photodetector to monitor the 0th order of the diffraction pattern. The spectrum of the source illuminating the gratings is computed by Fourier transforming the 0th order intensity as a function of the optical path difference. The vertical comb actuators have a travel range of 100 mu m under atmospheric pressure with 28V excitation, which yields a theoretical spectral resolution of 0.5nm in the visible and better than 5nm in the telecom wavelengths.Publication Open Access Acoustic superradiance from an optical-superradiance-induced vortex in a Bose-Einstein condensate(American Physical Society (APS), 2014) Ghazanfari, Nader; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We consider the scattering of an acoustic wave from a vortex induced by optical superradiance. The vortex is created by pumping a large amount of angular momentum with a Laguerre-Gaussian light beam in an atomic Bose-Einstein condensate. We derive the mean-field dynamical equations of the light-superfluid system, and obtain the equations governing the elementary excitation of the system, which result in a massless Klein-Gordon equation with source terms. This equation describes the propagation of the sound wave in an effective space-time. Employing a simplifying draining bathtub model for the vortex, we investigate the scattering of the acoustic wave in the vortex phase and obtain a condition for the acoustic superradiance. We conclude that Laguerre-Gaussian-beam-induced sudden transition from homogeneous to vortex state in the superfluid leads to a prominent observation of the acoustic superradiance.Publication Open Access Active invisibility cloaks in one dimension(American Physical Society (APS), 2015) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; Department of Physics; College of Sciences; 4231We outline a general method of constructing finite-range cloaking potentials which render a given finite-range real or complex potential, v(x), unidirectionally reflectionless or invisible at a wave number, k(0), of our choice. We give explicit analytic expressions for three classes of cloaking potentials which achieve this goal while preserving some or all of the other scattering properties of v(x). The cloaking potentials we construct are the sum of up to three constituent unidirectionally invisible potentials. We discuss their utility in making v(x) bidirectionally invisible at k(0) and demonstrate the application of our method to obtain antireflection and invisibility cloaks for a Bragg reflector.Publication Open Access Addendum to 'Unidirectionally invisible potentials as local building blocks of all scattering potentials'(American Physical Society (APS), 2014) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; Department of Physics; College of Sciences; 4231In [Phys. Rev. A 90, 023833 (2014)], we offer a solution to the problem of constructing a scattering potential v(x) which possesses scattering properties of one's choice at an arbitrarily prescribed wave number. This solution involves expressing v(x) as the sum of n <= 6 finite-range unidirectionally invisible potentials. We improve this result by reducing the upper bound on n from 6 to 4. In particular, we show that we can construct v(x) as the sum of up to n = 3 finite-range unidirectionally invisible potentials, unless if it is required to be bidirectionally reflectionless.Publication Open Access Adiabatic series expansion and higher-order semiclassical approximations in scattering theory(Institute of Physics (IOP) Publishing, 2014) Department of Mathematics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; College of Sciences; 4231The scattering properties of any complex scattering potential, nu: R -> C, can be obtained from the dynamics of a particular non-unitary two-level quantum system. S-nu. The application of the adiabatic approximation to S-nu yields a semiclassical treatment of the scattering problem. We examine the adiabatic series expansion for the evolution operator of S-v and use it to obtain corrections of arbitrary order to the semiclassical formula for the transfer matrix of S-nu. This results in a high-energy approximation scheme that unlike the semiclassical approximation can be applied for potentials with large derivatives.Publication Open Access Advanced materials and device architectures for magnetooptical spatial light modulators(Wiley-VCH, 2019) N/A; Department of Electrical and Electronics Engineering; Kharratian, Soheila; Onbaşlı, Mehmet Cengiz; Ürey, Hakan; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; N/A; 258783; 8579Faraday and Kerr rotations are magnetooptical (MO) effects used for rotating the polarization of light in transmission and reflection from a magnetized medium, respectively. MO effects combined with intrinsically fast magnetization reversal, which can go down to a few tens of femtoseconds or less, can be applied in magnetooptical spatial light modulators (MOSLMs) promising for nonvolatile, ultrafast, and high-resolution spatial modulation of light. With the recent progress in low-power switching of magnetic and MO materials, MOSLMs may lead to major breakthroughs and benefit beyond state-of-the-art holography, data storage, optical communications, heads-up displays, virtual and augmented reality devices, and solid-state light detection and ranging (LIDAR). In this study, the recent developments in the growth, processing, and engineering of advanced materials with high MO figures of merit for practical MOSLM devices are reviewed. The challenges with MOSLM functionalities including the intrinsic weakness of MO effect and large power requirement for switching are assessed. The suggested solutions are evaluated, different driving systems are investigated, and resulting device architectures are benchmarked. Finally, the research opportunities on MOSLMs for achieving integrated, high-contrast, and low-power devices are presented.Publication Open Access Advanced solid-state lasers 2019: focus issue introduction(Optical Society of America (OSA), 2020) Goodno, Gregory; Mirov, Sergey; Nilsson, Johan; Petersen, Alan; Sorokina, Irina; Taccheo, Stefano; Department of Electrical and Electronics Engineering; Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; College of Sciences; 23851This joint issue of Optics Express and Optical Materials Express features 17 state-of-the art articles written by authors who participated in the international conference Advanced Solid-State Lasers held in Vienna, Austria, from September 29 to October 3, 2019. This introduction provides a summary of these articles that cover numerous areas of solid-state lasers from materials research to sources and from design to experimental demonstration.Publication Open Access Analysis and optimization of diode end-pumped solid-state lasers: applicationto Nd3+ : YVO4 lasers at 1064 and 1342 nm(Society of Photo-optical Instrumentation Engineers (SPIE), 2005) Buhours, S.; Department of Physics; Department of Electrical and Electronics Engineering; Sennaroğlu, Alphan; Kurt, Adnan; Faculty Member; Teaching Faculty; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; 23851; 194455We describe a systematic procedure that uses experimental and numerical methods to analyze the continuous-wave power performance of diode end-pumped solid-state lasers. For the general case, saturation, excited-state absorption, and thermal lensing effects are considered and integral equations are derived to study the evolution of the pump and laser beams in the gain medium. As an application of the method, we consider two different diode end-pumped Nd3+:YVO4 lasers operating at 1064 and 1342 nm. Experimental efficiency data were first analyzed to determine the stimulated emission cross sections and the resonator losses. The best-fit laser parameters were then used to calculate the optimum crystal length that maximizes the output power of the laser. The described method should prove useful in the design of a wide range of efficient diode-pumped solid-state lasers.Publication Open Access Angular-momentum-driven chaos in small clusters(American Physical Society (APS), 1998) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The effects of the rotational motion on the chaotic behavior of triatomic Lennard-Jones clusters are studied. A set of initial momentum distributions with tunable parameters is chosen to correspond to various rigid-body rotations around symmetry axes of the cluster. By smoothly varying the direction of the initial kicks given to the cluster, periodic transitions between regular and chaotic regimes are obtained. A study of initial conditions leading up to such transitions shows that the major factor that determines the extent of the chaotic behavior is the initial partitioning of the kinetic energy between the rotational and vibrational motion. From the analysis of the time evolution of various properties it is concluded that the basic role of this initial partitioning is to control the energy transfer between the kinetic and the potential energy.Publication Open Access Antibunching via cooling by heating(American Physical Society (APS), 2022) Department of Physics; Müstecaplıoğlu, Özgür Esat; Naseem, Muhammad Tahir; Faculty Member; Department of Physics; College of Sciences; 1674; N/AWe investigate statistics of the photon (phonon) field undergoing linear and nonlinear damping processes. An effective two-photon (phonon) nonlinear "cooling by heating"process is realized from linear damping by spectral filtering of the heat baths present in the system. This cooling process driven by incoherent quantum thermal noise can create quantum states of the photon field. In fact, for high temperatures of the spectrally filtered heat baths, sub-Poissonian statistics with strong antibunching in the photon (phonon) field are reported. This notion of the emergence and control of quantumness by incoherent thermal quantum noise is applied to a quantum system comprised of a two-level system and a harmonic oscillator or analogous optomechanical setting. Our analysis may provide a promising direction for the preparation and protection of quantum features via nonlinear damping that can be controlled with incoherent thermal quantum noise.