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Publication Metadata only 5-nj Femtosecond Ti3+:sapphire laser pumped with a single 1 W green diode(Iop Publishing Ltd, 2018) N/A; N/A; Department of Physics; Department of Physics; Muti, Abdullah; Kocabaş, Aşkın; Sennaroğlu, Alphan; PhD Student; Faculty Member; Faculty Member; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 227753; 23851We report a Kerr-lens mode-locked, extended-cavity femtosecond Ti3+:sapphire laser directly pumped at 520 nm with a 1 W AlInGaN green diode. To obtain energy scaling, the short x-cavity was extended with a q-preserving multi-pass cavity to reduce the pulse repetition rate to 5.78 MHz. With 880 mW of incident pump power, we obtained as high as 90 mW of continuous-wave output power from the short cavity by using a 3% output coupler. In the Kerr-lens mode-locked regime, the extended cavity produced nearly transform-limited 95 fs pulses at 776 nm. The resulting energy and peak power of the pulses were 5.1 nJ and 53 kW, respectively. To our knowledge, this represents the highest pulse energy directly obtained to date from a mode-locked, single-diode-pumped Ti3+:sapphire laser.Publication Metadata only 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; 22542Aerogels-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.Publication Metadata only Analysis of the knight shift data on Li and Zn substituted YBa2Cu3O6+x(Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/AThe Knight shift data on Li and Zn substituted YBa2Cu3O6+x are analyzed using an itinerant model with short-range antiferromagnetic correlations. The model parameters, which are determined by fitting the experimental data on the transverse nuclear relaxation rate T-2(-1) of pure YBa2Cu3O6+x, are used to calculate the Knight shifts for various nuclei around a nonmagnetic impurity located in the CuO2 planes. The calculations are carried out for Li and Zn impurities substituted into optimally doped and underdoped YBa2Cu3O6+x. The results are compared with the Li-7 and Y-89 Knight shift measurements on these materials. (C) 2001 Elsevier Science B.V. All rights reserved.Publication Open Access Bistable behavior of a two-mode Bose-Einstein condensate in an optical cavity(Maik Nauka/Interperiodica Publishing, 2013) Safaei, S.; Tanatar, B.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We consider a two-component Bose-Einstein condensate in a one-dimensional optical cavity. Specifically, the condensate atoms are taken to be in two degenerate modes due to their internal hyperfine spin degrees of freedom and they are coupled to the cavity field and an external transverse laser field in a Raman scheme. A parallel laser also excites the cavity mode. When the pump laser is far detuned from its resonance atomic transition frequency, an effective nonlinear optical model of the cavity-condensate system is developed under the discrete mode approximation (DMA), while matter-field coupling has been considered beyond the rotating wave approximation. By analytical and numerical solutions of the nonlinear dynamical equations, we examine the mean cavity field and population difference (magnetization) of the condensate modes. The stationary solutions of both the mean cavity field and normalized magnetization demonstrate bistable behavior under certain conditions for the laser pump intensity and matter-field coupling strength.Publication Metadata only Bose-einstein condensate in a harmonic trap with an eccentric dimple potential(Institute of Physics (IOP) Publishing, 2008) Uncu, H.; Tarhan, D.; Demiralp, E.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We investigate Bose-Einstein condensation of noninteracting gases in a harmonic trap with an offcenter dimple potential. We specifically consider the case of a tight and deep dimple potential, which is modeled by a point interaction. This point interaction is represented by a Dirac delta function. The atomic density, chemical potential, critical temperature and condensate fraction, and the role of the relative depth and the position of the dimple potential are analyzed by performing numerical calculations.Publication Open Access Broadly tunable continuous-wave solid-state red source based on intracavity-doubled Cr (4+): forsterite laser(Society of Photo-optical Instrumentation Engineers (SPIE), 2002) Department of Physics; Sennaroğlu, Alphan; Faculty Member; Department of Physics; College of Sciences; 23851This work describes the development and characterization of a continuous-wave (cw) room-temperature intracavity-doubled Cr4+:forsterite laser which produces broadly tunable red radiation. Such a source is potentially important in spectroscopy, display technologies, and medical applications. In the experiments, a 2-cm-long Cr4+:forsterite crystal was placed in an astigmatically compensated x-cavity which was end-pumped by a 1064-nm Nd:YAG laser. The crystal which had a small-signal pump absorption of 68% was maintained at 20 degreesC. An intracavity Brewster-cut SF10 prism was used to tune the output of the laser. Intracavity frequency doubling was achieved by using a periodically poled lithium niobate (PPLN) crystal which had 8 different poling periods. The PPLN crystal was placed inside the resonator between a curved folding mirror and the curved output coupler. The transmission of the output coupler was 2.6% at 1260 nm. The PPLN temperature was maintained at 188 degreesC. By translating the PPLN crystal through sections with different poling periods, second harmonic generation was obtained in the wavelength region between 613 and 655 run. With an incident pump power of 6.8 W at 1064 rim, the Cr4+:forsterite laser produced 245 mW of cw output power at 1260 nm and intracavity frequency doubling yielded 45 mW at 630 nm.Publication Metadata only 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; 23851We 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.Publication Open Access Collective excitations of a laser driven atomic condensate in an optical cavity(Maik Nauka/Interperiodica Publishing, 2013) Öztop, B.; Türeci, H. E.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We theoretically examine collective excitations of an optically driven atomic Bose-Einstein condensate, coupled to a high-finesse optical cavity. This open system has been recently used for the experimental demonstration of the Dicke superradiance of cavity photons, which is simultaneously and mutually triggered by spontaneous breaking of translational symmetry of the condensate into a crystalline order. We first develop a Hartree-Fock mean field dynamical model of the physical system. Using this model, we compute the dynamics of the cavity photons, the condensate density profile and the Dicke phase transition diagram. Both the imaginary-time and real-time evolution methods are used in the calculations. Collective excitations are determined by the solving Bogoliubov-de Gennes equations. The spectrum, softening of the modes and energetic hierarchy of excitations are determined.Publication Metadata only 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/AThe 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.Publication Open Access Controlled photoluminescence in amorphous-silicon-nitride microcavities(American Institute of Physics (AIP) Publishing, 2001) Tanrıseven, S.; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855Narrow-band and enhanced photoluminescence have been observed in hydrogenated amorphous-silicon-nitride microcavities. The distributed Bragg reflectors were fabricated using alternating layers of hydrogenated amorphous-silicon nitride and hydrogenated amorphous-silicon oxide. The microcavity resonance wavelength was designed to be at the maximum of the bulk hydrogenated amorphous-silicon-nitride luminescence spectrum. At the microcavity resonance, the photoluminescence amplitude is enhanced, while the photoluminescence linewidth is reduced with respect to the bulk hydrogenated amorphous-silicon nitride. (C) 2001 American Institute of Physics.