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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Sub-100-fs pulse generation from a Kerr-lens mode-locked Alexandrite laser(Optica Publishing Group (formerly OSA), 2018) Demirbaş Ümit; N/A; N/A; N/A; Department of Physics; Cihan, Can; Muti, Abdullah; Toker, Işınsu Baylam; Sennaroğlu, Alphan; PhD Student; 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; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 23851We report, to the best of our knowledge, the shortest pulses obtained from a Kerr-lens mode-locked multipass-cavity Alexandrite laser operating near 750 nm. The resonator produced 70-fs pulses with a time-bandwidth product of 0.331.Publication Metadata only Characterization of fluid mixtures at high pressures using frequency response of microcantilevers(2017) Bozkurt, Asuman Aşıkoğlu; Jonas, Alexandr; Department of Chemical and Biological Engineering; N/A; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Eris, Gamze; Baloch, Shadi Khan; Kiraz, Alper; Alaca, Burhanettin Erdem; Erkey, Can; Researcher; PhD Student; Faculty Memeber; Faculty Member; Faculty Member; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Engineering; N/A; N/A; 22542; 115108; 29633The frequency response of ferromagnetic nickel microcantilevers immersed in binary mixtures of carbon dioxide (CO2) and nitrogen (N-2) at 308 K and pressures up to 23 MPa was investigated. Experimental data were analyzed using the model developed by Sader for a clamped oscillatory beam immersed in a fluid and a very good agreement between the measured resonant frequencies and quality factors (Q factors) and the theoretical predictions of the model with cantilever characteristic parameters regressed from experimental data was observed. This suggested that the data could be used to simultaneously measure the density and the viscosity of fluid mixtures over a wide range of pressures. Subsequently, density and viscosity of binary mixtures of CO2 and N-2 were determined using N-2 as the reference fluid and compared to the predictions of Gerg equation of state and Chung equation, respectively. For the studied fluids with different compositions, the average relative difference between the experimental density values and the values predicted using Gerg equation of state and NIST database ranged from 1.0 to 13%. The average relative difference between the experimental viscosity values and the values obtained using Chung equation and NIST database ranged from 2.4 to 15%. Since the resonant frequency and Q factor were found to vary with composition at a fixed temperature and pressure, the technique can in principle also be used to measure the composition of a binary mixture at a fixed temperature and pressure. The study represents the first systematic attempt to use microcantilevers for the characterization of high-pressure fluid mixtures and paves the way for devising portable sensors for in-line monitoring of thermophysical properties and composition of fluid mixtures under a wide range of environmental conditions. (C) 2017 Elsevier B.V. All rights reserved.Publication Metadata only Graphene mode-locked femtosecond Cr:LiSAF laser(Optical Society of America (OSA), 2015) Kakenov, N.; Kocabas, C.; Demirbas, U.; N/A; Department of Physics; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851We report the first demonstration of femtosecond pulse generation from a Cr:LiSAF laser mode-locked with a monolayer graphene saturable absorber. Nearly transform-limited 72-fs pulses were generated at 850 nm with only two 135-mW pump diodes.Publication Metadata only Symmetric meandering distributed feedback structures for silicon photonic circuits(Ieee-Inst Electrical Electronics Engineers Inc, 2020) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Physics; Chaudhry, Muhammad Rehan; Zakwan, Muhammad; Onbaşlı, Mehmet Cengiz; Serpengüzel, Ali; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; N/A; 258783; 27855Fano lineshapes and electro-magnetically induced transparency-like peaks in the transmittance of a transverse electric polarization silicon-on-insulator symmetric meandering distributed feedback photonic structure are demonstrated. The coupling constants at the five identical directional couplers are varied to obtain the desired spectral responses. The numerically simulated and experimentally measured transmittance spectra are in good agreement with each other. The numerically calculated and experimentally measured insertion loss for the symmetric meandering distributed feedback structure with directional coupler coupling length L-c = 10 mu m are respectively -5 dB and -17 dB, including the grating couplers. Fano lineshapes with mode splitting is observed at directional coupler coupling constant value C of 0.24. For coupling constant value of C similar to 0.78, electro-magnetically induced transparency-like peaks are observed, and spectrally adjusted by varying the directional coupler coupling length. Fano lineshapes show an extinction ratio of more than 26 dB and slope ratio of 368 dB/nm. Electro-magnetically induced transparency-like peaks show a quality-factor on the order of 5 x 10(4). The symmetric meandering distributed feedback structure shows promise for possible applications as an optical switch, and an optical filter in wavelength division multiplexing and data networks, as well as optical sensors in optical diagnostics, using silicon photonics.Publication Metadata only Elastic scattering from germanium microspheres in the terahertz region(IEEE, 2016) N/A; N/A; Department of Physics; Bukhari, Syed Sultan Shah; Chaudhry, Muhammad Rehan; Serpengüzel, Ali; 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; 27855N/APublication Metadata only Subpicosecond pulse generation from a chirped-pulse multipass-cavity Cr4+:forsterite oscillator(IEEE, 2011) Aktürk, Selçuk; 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 produced the highest pulse energy directly generated from a room-temperature, mode-locked Cr4+:forsterite oscillator. The chirped-pulse, multipass-cavity, 1261-nm oscillator operated at 4.9 MHz and produced 81-nJ pulses which could be externally compressed to 620 fs.Publication Metadata only Optical sensors based on palladium and polymer-coated optical fiber resonators(Spie-Int Soc Optical Engineering, 2019) Eryürek, Mustafa; N/A; Department of Physics; Department of Chemistry; Department of Chemistry; Department of Physics; Bavili, Nima; Morova, Berna; Yılgör, İskender; Yılgör, Emel; Kiraz, Alper; PhD Student; Researcher; Faculty Member; Researcher; Faculty Member; Department of Chemistry; Department of Physics; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; College of Science; College of Sciences; College of Sciences; College of Sciences; N/A; 152935; 24181; N/A; 22542In this work, we present robust and easy-to-fabricate optical gas and vapor sensors based on optical fiber resonators (OFR) coated with palladium (Pd) thin films, Pd micro-particles and polymer brushes (PB). Pd based sensors are used for hydrogen (H-2) gas detection in concentration range of 0% to 1% and polymer brush-coated OFR are used for detection of vapor in concentration range of 0 to 25%. Sensing mechanism of these sensors is based on spectral shift of resonance wavelength which are called whispering gallery modes (WGMs). This spectral shift is due to volume expansion of the sensing material. Tapered fiber is used in order to excite WGMs in coated OFRs. Good sensitivity and repeatability results are obtained for all three types of sensors.Publication Metadata only Nd3+ -doped tellurite glass laser at 1.37 um(IEEE, 2009) N/A; Department of Physics; Çankaya, Hüseyin; Sennaroğlu, Alphan; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; School of Medicine; N/A; 205925We have demonstrated for the first time to our knowledge, lasing at 1.37 mu m in a neodymium-doped tellurite glass host. the slope efficiency and emission cross section were determined to be 5.5% and 1.57x10(-20)cm(2), respectively.Publication Metadata only Graphene mode-locked diode-pumped Cr: LiSAF laser at 857 nm(Optica Publishing Group (formerly OSA), 2014) Kakenov, N.; Kocabas, C.; Demirbas, U.; N/A; Department of Physics; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851N/APublication Metadata only Gain-matched output couplers (GMOCs) for efficient and Robust Kerr-Lens mode-locking of Cr:LiSAF lasers(Institute of Electrical and Electronics Engineers (IEEE), 2014) Chen, Li-Jin; Sumpf, Bernd; Erbert, Goetz; Leitenstorfer, Alfred; Kaertner, Franz X.; Demirbaş, Ümit; N/A; N/A; N/A; Department of Physics; Cihan, Can; Beyatlı, Ersen; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; PhD 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; College of Sciences; N/A; 229317; N/A; 23851We report efficient and robust Kerr-lens mode-locking of single-mode and tapered diode-pumped Cr:LiSAF lasers by using gain-matched output couplers. Sub-15-fs pulses were generated with peak powers above 60-kW and optical-to-optical conversion efficiencies up to 21%.