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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 Silicon microsphere photonics - art. no. 65931J(Society of Photo-optical Instrumentation Engineers (SPIE), 2007) Department of Physics; Department of Electrical and Electronics Engineering; Serpengüzel, Ali; Kurt, Adnan; Ayaz, Ulaş Kemal; Faculty Member; Teaching Faculty; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; 27855; 194455; N/AElectrophotonic integrated circuits (EPICs), or alternatively, optoelectronic integrated circuit (OEICs) are the natural evolution of the microelectronic integrated circuit (IC) with the added benefit of photonic capabilities. Traditionally, the microelectronics IC industry has been based on group IV silicon, whereas the microphotonics industry on group III-V semiconductors. However, silicon based photonic microdevices have been making strands in "siliconizing" photonics. Silicon microspheres with their high quality factor whispering gallery modes (WGMs), are ideal candidates for wavelength division multiplexing (WDM) in the standard near-infrared telecommunications bands. In our experiments, we are using silicon microspheres with a refractive index of 3.48 and a radius of 500 micrometers. The optical resonances of the silicon microspheres provide the necessary narrow linewidths, that are needed for high resolution WDM applications. Potential WDM applications include filters, modulators, switches, detectors, and possibly light sources.Publication Open Access Effects of Bloch's hydrodynamic model on surface plasmon polariton dispersion curve and enhanced transmission of light through single nano-apertures(Society of Photo-optical Instrumentation Engineers (SPIE), 2009) Department of Physics; Çetin, Arif Engin; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; N/A; 1674We have studied the surface plasmon theory with Bloch's hydrodynamic model. The results of the analysis done by Bloch model have been compared with the ones done with Drude model and the dominant differences between two models in valid frequency range have been shown. The transmittance of the slit embedded in a metal layer has been investigated by these models and the differences have been emphasized. An electron density dependent parameter defined by Bloch model has been used to control the transmission behavior of the light through nano-apertures. A system consisting of a nano-slit formed in a metal layer with a periodically textured surface used for beam focusing has been introduced and how the focusing capacity of the system is controlled by the parameter defined by Bloch model has been shown.Publication Open Access Temperature control in dissipative cavities by entangled dimers(American Chemical Society (ACS), 2019) Dağ, Ceren B.; Niedenzu, Wolfgang; Özaydın, Fatih; Kurizki, Gershon; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We show that the temperature of a cavity field can be drastically varied by its interaction with suitably entangled atom pairs (dimers) traversing the cavity under realistic atomic decoherence. To this end we resort to the hitherto untapped resource of naturally entangled dimers whose state can be simply controlled via molecular dissociation, collisions forming the dimer, or unstable dimers such as positronium. Depending on the chosen state of the dimer, the cavity-field mode can be driven to a steady-state temperature that is either much lower or much higher than the ambient temperature, despite adverse effects of cavity loss and atomic decoherence. Entangled dimers enable much broader range of cavity temperature control than single "phaseonium" atoms with coherently superposed levels. Such dimers are shown to constitute highly caloric fuel that can ensure high efficiency or power in photonic thermal engines. Alternatively, they can serve as controllable thermal baths for quantum simulation of energy exchange in photosynthesis or quantum annealing.Publication Open Access Large spectral tuning of liquid microdroplets by local heating with a focused infrared laser(Society of Photo-optical Instrumentation Engineers (SPIE), 2008) Department of Physics; Department of Electrical and Electronics Engineering; Kiraz, Alper; Karadağ, Yasin; Yorulmaz, Saime Çiğdem; Muradoğlu, Metin; Faculty Member; PhD Student; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; 22542; N/A; N/A; 46561Large deformations can easily be introduced in liquid microdroplets by applying relatively small external forces or controlling the evaporation/condensation kinetics. This makes liquid microdroplets attractive to serve as the building blocks of largely tunable optical switches or filters that are essential in optical communication systems based on wavelength division multiplexing. Solid optical microcavities have not found large use in these applications, mainly due to their rigid nature. The fact that liquid microdroplets are low-cost and disposable can also prove to be important in mass production of these photonic devices. Here, we show that local heating with an infrared laser can be used to largely tune the whispering gallery modes (WGMs) of water/glycerol or salty water microdroplets standing on a superhydrophobic surface. In the scheme presented, a liquid microdroplet kept in a humidity chamber is stabilized on a superhydrophobic surface, and an infrared laser beam is focused near tire center of the microdroplet. As a, result of the local treating, the temperature of the liquid microdroplet increases, and the water content in the liquid microdroplet evaporates until a new equilibrium is reached. At the new equilibrium state, the non-volatile component, (i.e. glycerol or salt) attains a higher concentration in the liquid microdroplet. We report tunability over large spectral ranges up to 30 run at around 590 nm. For salty water microdroplets the reported spectral timing mechanism is almost fully reversible, while for tire case of glycerol/water microdroplets the spectral timing mechanism can be made highly reversible when the chamber is saturated with glycerol vapor and the relative water humidity approaches unity.Publication Open Access Tunable optofluidic microlasers based on optically stretched emulsion droplets(Society of Photo-optical Instrumentation Engineers (SPIE), 2013) Brzobohaty, Oto; Jezek, Jan; Pilat, Zdenek; Zemanek, Pavel; Department of Physics; Department of Electrical and Electronics Engineering; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; N/A; 22542We introduce tunable optofluidic microlasers based on optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. Optically trapped microdroplets of oil emulsified in water and stained with fluorescent dye act as active ultrahigh-Q optical resonant cavities hosting whispering gallery modes (WGMs) which enable dye lasing with low threshold pump powers. In order to achieve tunable dye lasing, the droplets are pumped with a pulsed green laser beam and simultaneously stretched by light in the dual-beam trap. For a given stretching power, the magnitude of the droplet deformation is dictated by the interfacial tension between the droplet and the host liquid which is adjustable by adding surfactants. Increase of power of the dual-beam trap causes a directly proportional change of the droplet stretching deformation. Subsequently, resonant path lengths of different WGMs propagating in the droplet are modified, leading to shifts in the corresponding microlaser emission wavelenghts. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of wavelength tuning depends on the position of the pump beam focus on the droplet, consistent with the deformation of originally spherical droplet towards a prolate spheroid. In addition, we study the effects of changes of the droplet and immersion medium temperature on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength.Publication Open Access Dye lasing in optically manipulated liquid aerosols(Society of Photo-optical Instrumentation Engineers (SPIE), 2013) McGloin, David; Anand, Suman; Department of Physics; Department of Electrical and Electronics Engineering; Karadağ, Yasin; Aas, Mehdi; Jonas, Alexandr; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; N/A; N/A; 22542We present dye lasing from optically manipulated glycerol-water aerosols with diameters ranging between 7.7 and 11.0 mu m confined in optical tweezers. While being optically trapped near the focal point of an infrared laser, the droplets stained with Rhodamine B were pumped with a Q-switched green laser and their fluorescence emission spectra featuring whispering gallery modes (WGMs) were recorded with a spectrograph. Nonlinear dependence of the intensity of the droplet WGMs on the pump laser fluence indicates dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by adjusting the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.Publication Open Access Cadmium-free and efficient Type-II InP/ZnO/ZnS quantum dots and their application for LEDs(American Chemical Society (ACS), 2021) Ritter, Maximilian; Şahin, Mehmet; Ow-Yang, Cleva W.; Lechner, Rainer T.; Department of Electrical and Electronics Engineering; Department of Physics; N/A; N/A; Nizamoğlu, Sedat; Sennaroğlu, Alphan; Eren, Güncem Özgün; Sadeghi, Sadra; Jalali, Houman Bahmani; Han, Mertcan; Toker, Işınsu Baylam; Melikov, Rustamzhon; Önal, Asım; Öz, Fatma; Faculty Member; Faculty Member; PhD Student; PhD Student; Master Student; PhD Student; Department of Electrical and Electronics Engineering; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Engineering; College of Sciences; Graduate School of Sciences and Engineering; 130295; 23851; N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/AIt is a generally accepted perspective that type-II nanocrystal quantum dots (QDs) have low quantum yield due to the separation of the electron and hole wavefunctions. Recently, high quantum yield levels were reported for cadmium-based typeII QDs. Hence, the quest for finding non-toxic and efficient type-II QDs is continuing. Herein, we demonstrate environmentally benign type-II InP/ZnO/ZnS core/shell/shell QDs that reach a high quantum yield of similar to 91%. For this, ZnO layer was grown on core InP QDs by thermal decomposition, which was followed by a ZnS layer via successive ionic layer adsorption. The small-angle Xray scattering shows that spherical InP core and InP/ZnO core/ shell QDs turn into elliptical particles with the growth of the ZnS shell. To conserve the quantum efficiency of QDs in device architectures, InP/ZnO/ZnS QDs were integrated in the liquid state on blue light-emitting diodes (LEDs) as down-converters that led to an external quantum efficiency of 9.4% and a power conversion efficiency of 6.8%, respectively, which is the most efficient QD-LED using type-II QDs. This study pointed out that cadmium-free type-II QDs can reach high efficiency levels, which can stimulate novel forms of devices and nanomaterials for bioimaging, display, and lighting.Publication Open Access Excitation of silicon microspheres resonances with Femtosecond laser fabricated glass waveguides(Society of Photo-optical Instrumentation Engineers (SPIE), 2016) Sotillo, Belen; Bharadwaj, Vibhav; Eaton, Shane M.; Ramponi, Roberta; Department of Physics; Çirkinoğlu, Hüseyin Ozan; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855Optical waveguides were fabricated with femtosecond pulsed lasers on glass and characterized by transmission measurements. Glass waveguides were later used for excitation of the whispering gallery modes in a silicon microsphere. The coupling between the silicon microsphere and the femtosecond laser inscribed optical waveguide was simulated in both 90 degrees elastic scattering and 0 degrees transmission spectra. The silicon microsphere whispering gallery modes are available for both in the transverse electric and transverse magnetic polarizations with a spectral mode spacing of 0.25 nm. Optical resonances on silicon microsphere integrated with femtosecond laser written optical waveguides may lead to future quantum optical communication devices.Publication Open Access Emission tunable, cyto/hemocompatible, near-IR-emitting Ag2S quantum dots by aqueous decomposition of DMSA(Royal Society of Chemistry (RSC), 2014) Sevrin, Chantal; Department of Chemistry; Department of Physics; Birer, Özgür; Hocaoğlu, İbrahim; Kiraz, Alper; Acar, Havva Funda Yağcı; Duman, Fatma Demir; Researcher; PhD Student; Faculty Member; Department of Chemistry; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; College of Sciences; Graduate School of Sciences and Engineering; N/A; N/A; N/A; 22542; N/A; 178902Size tunable aqueous Ag2S quantum dots emitting in the near-infrared region were synthesized through decomposition of meso-2,3-dimercaptosuccinic acid (DMSA) in water. The resulting NIR QDs are highly cyto- and hemocompatible, have quantum yields as high as 6.5% and are effective optical imaging agents based on in vitro evaluation.