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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.Electrical electronics engineering

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    Optical modulation with silicon microspheres
    (IEEE-Inst Electrical Electronics Engineers Inc, 2009) Gürlü, Oğuzhan; N/A; Department of Physics; Yüce, Emre; Serpengüzel, Ali; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; 245435; 27855
    In this letter, a silicon microsphere coupled to a silica optical fiber half coupler has been characterized for electrooptical modulation in the L-band at 1.55 mu m. Electrooptical modulation of the transmitted and the 90 degrees elastic scattered signals for both the TE and the TM polarizations of the microsphere resonances has been observed.
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    Investigation of the ultrafast response and saturable absorption of voltage-controlled graphene
    (Optica Publishing Group (formerly OSA), 2018) Kakenov N.; Kocabas C.; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD Student; 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; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 23851
    Ultrafast pump-probe measurements show that at a bias voltage of 1V, voltage reconfigurable graphene supercapacitors can operate as fast saturable absorbers with adjustable insertion loss over an ultrabroad spectral range from 630 to 1100 nm.
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    Mid-infrared elastic scattering from germanium microspheres
    (IEEE, 2016) N/A; N/A; N/A; N/A; Department of Physics; Zakwan, Muhammad; Bayer, Mustafa Mert; Anwar, Muhammad Sohail; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; PhD Student; Master Student; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 27855
    Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, especially in the mid-infrared (mid-IR) wavelengths. As a semiconductor material for microphotonics applications [1], germanium is particularly attractive owing to its large nonlinearity, high optical damage threshold compared with traditional nonlinear glass materials, and above all, its broad transparency window, extending from the near-IR into the mid-IR. Germanium based optical components have found numerous applications in imaging systems operating in the mid-IR wavelengths, where the principal natural greenhouse gases do not exhibit strong absorption. These applications include rapid sensing and diagnosis [2,] [3], industrial process controls, environmental monitors to hazardous chemical detection [4]. Germanium also is a good electromagnetic shielding material, an attribute that has become increasingly important for modern military applications, where other signals (within the millimeter and centimeter wavelength range) can be strong enough to interfere with nearby IR systems. Elastic light scattering from a germanium microsphere has already been observed in the near-IR [5]. Here, elastic light scattering from a germanium microsphere in the mid-IR region is numerically analyzed using generalized Lorenz-Mie theory (GLMT) [6]. Light interaction with microspheres of various materials is of much interest because of their photonic properties [7]. Germanium has a refractive index of 4, which is even higher than the refractive index of silicon (3.5) in the mid-IR region. The higher refractive index results in higher quality factor morphology dependent resonances (MDRs). A higher value of Q indicates a longer lifetime of the photons trapped inside the cavity and a narrower MDR. Here, the MDRs are observed numerically in the transverse magnetically (TM) and transverse electrically (TE) polarized 90° elastic scattering and 0° transmission for a 40 µm radius germanium microsphere in the mid-IR wavelengths ranging from 5.4 µm to 5.6 µm [8]. The mode spacing of approximately 41 nm between the resonances with the same radial mode order and consecutive polar mode number shows good correlation with the optical size of the germanium microsphere. The germanium microsphere with its high quality factor MDRs can be suitable for optical monitoring and sensing applications in the mid-IR, which require a high spectral resolution [9].
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    Ruby microsphere and liquid cyrstal based tunable optical filter
    (Ieee, 2009) Beccherelli, Romeo; Department of Physics; N/A; N/A; Serpengüzel, Ali; Murib, Mohammed Sharif; Hüseyinoğlu, Ersin; Faculty Member; PhD Student; Master Student; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 27855; N/A
    A microsphere placed in a liquid crystal is used as an optical filter. By changing the refractive index of the liquid cyrstal, the resonance frequency of the sphere is controlled.
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    Graphene supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Society of America (OSA), 2014) Ozharar, Sarper; Ozan Polat E.; Kocabas, Coskun; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; 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; 23851
    For the first time to our knowledge, we employed a graphene supercapacitor as a voltage controlled saturable absorber at bias voltages of 0.5-1V to generate 84-fs pulses from a solid-state laser near 1255 nm.
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    Experimental and numerical investigation of thermal effects in end-pumped Cr/sup 4+/: forsterite lasers near room temperature
    (IEEE-Inst Electrical Electronics Engineers Inc, 1998) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/A
    The results of a study which employs both experimental and theoretical methods to investigate the role of thermal effects in room-temperature Cr4+:forsterile lasers are presented. A novel model was developed to calculate the incident threshold pump power required to attain oscillation by taking into account absorption saturation and pump-induced thermal loading in the gain medium, Experimentally, the incident threshold pump power was measured as a function of the crystal boundary temperature for three Cr4+:forsterite laser crystals with different small-signal differential absorption coefficients alpha(p0) and/or cross-sectional areas. Excellent agreement was obtained between theory and experiment for values of the stimulated emission cross section comparable to those from previously reported data. The model was then used to numerically determine the optimum value of alpha(p0) which minimizes the incident threshold pump power in room-temperature Cr4+:forsterite lasers, At a crystal boundary temperature of 15 degrees C, the optimum value of alpha(p0) was determined to be 0.64 cm(-1) for a 2-cm-long Cr4+:forsterite crystal, corresponding to an unsaturated absorption of 72%. The use of crystals with an optimum absorption coefficient should lead to the realization of highly efficient CW Cr4+:forsterite lasers at room temperature.
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    Dual-wavelength temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser
    (IEEE-Inst Electrical Electronics Engineers Inc, 2018) N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Canbaz, Ferda; Sennaroğlu, Alphan; 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; 23851
    We provide a detailed experimental investigation of the energy efficiency and rich temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser pumped near 800 nm. A tunable Ti3+:sapphire laser was used to determine the full excitation spectrum and the optimum pumping bands for the 1.5% Tm3+:Lu2O3 ceramic gain medium. These bands were centered at 774, 796, and 811 nm. The highest output pulse energy was obtained when the pump wavelength was set to 796 nm. In the experiments, a free-running x-cavity was used to investigate the energy efficiency of the Tm3+:Lu2O3 ceramic laser. Extracavity grating-dispersed output and prism-tuned resonator were used to further assess the role of cross-relaxation for the 1.5% Tm3+:Lu2O3 ceramic. Finally, we demonstrate that as the pump energy was increased, a transition occurred from-single-wavelength output (2068 nm) to dual-wavelength multipulse output (2068 and 1968 nm). We performed systematic temporal and spectral characterization measurements by using the free-running resonator, extracavity-grating-dispersed laser output, and prism-tuned resonator to investigate how the laser pulses at 1968 and 2068 nm evolved in time. A plane-wave rate equation model was further used to investigate the temporal dynamics of the Tm3+:Lu2O3 ceramic laser and provided predictions in qualitative agreement with experimental data.
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    Photonic studies on polymer-coated sapphire-spheres: a model system for biological ligands
    (Elsevier, 2015) Murib, M. S.; Yeap, W. S.; Martens, D.; Liu, X.; Bienstman, P.; Fahlman, M.; Schöning, M. J.; Michiels, L.; Haenen, K.; Wagner, P.; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855
    In this study we show an optical biosensor concept, based on elastic light scattering from sapphire micro-spheres. Transmitted and elastic scattering intensity of the microspheres (radius 500 mu m, refractive index 1.77) on an optical fiber half coupler is analyzed at 1510 nm. The 0.43 nm angular mode spacing of the resonances is comparable to the angular mode spacing value estimated using the optical size of the microsphere. The spectral linewidths of the resonances are in the order of 0.01 am, which corresponds to quality factors of approximately 10(5). A polydopamine layer is used as a functionalizing agent on sapphire microspherical resonators in view of biosensor implementation. The varying layer thickness on the microsphere is determined as a function of the resonance wavelength shift. It is shown that polymer functionalization has a minor effect on the quality factor. This is a promising step toward the development of an optical biosensor.
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    Optical channel dropping with a silicon microsphere
    (Ieee-Inst Electrical Electronics Engineers Inc, 2005) N/A; N/A; Department of Physics; Department of Physics; Yılmaz, Yiğit Ozan; Demir, Abdullah; Kurt, Adnan; Serpengüzel, Ali; Master Student; Master Student; Teaching Faculty; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 194455; 27855
    We report the observation of morphology-dependent resonances from silicon microspheres. The dropped channels are observed both in the transmission and elastic scattering spectra in the O-band. The filter drops approximately 23% of the power at the resonance wavelength. The highest observed quality factor for the morphology-dependent resonances was on the order of 10(5). These resonances have a linewidth of 0.007 nm and a mode spacing of 0.19 nm.
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    Direct experimental determination of the optimum chromium concentration in continuous-wave Cr2(+): ZnSe lasers
    (Institute of Electrical and Electronics Engineers (IEEE), 2007) Demirbaş, Ümit; Department of Physics; Department of Chemistry; Department of Chemistry; Sennaroğlu, Alphan; Somer, Mehmet Suat; Kurt, Adnan; Faculty Member; Faculty Member; Teaching Faculty; Department of Physics; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; 23851; 178882; 194455
    We employed several experimental techniques to measure the concentration dependence of the important laser parameters, and directly determine the optimum ion concentration for continuous-wave (CW) operation in room temperature Cr2+:ZnSe lasers. By using diffusion doping, 40 polycrystalline Cr2+ :ZnSe samples with ion concentrations in the range of 0.8 x 10(18) to 66 x 10(18) ions/cm(3) were prepared and used in this paper. Based on the spectroscopic measurements, empirical formulae showing the concentration dependence of the passive laser losses, fluorescence lifetime, and the fluorescence efficiency were obtained. By using the fluorescence efficiency data, the optimum chromium concentration, which maximizes the 2400-nm fluorescence intensity at a fixed excitation power, was determined to be 6 x 10(18) ions/cm(3). The dependence of the optimum concentration on sample length was further discussed. The CW power performance of the samples was also evaluated. At an incident pump power of 2.1 W, the optimum concentration for lasing was determined to be 8.5 X 10(18) ions/cm' that was in good agreement with the fluorescence measurements. The predictions of the fluorescence analysis and laser power measurements were in good agreement at low chromium concentrations. The observed discrepancy at higher doping levels was attributed to thermal loading.