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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 Analysis of thermal fields in orthogonal machining with infrared imaging(Elsevier Science Sa, 2008) Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Physics; Lazoğlu, İsmail; Serpengüzel, Ali; N/A; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Manufacturing and Automation Research Center (MARC); Manufacturing and Automation Research Center (MARC); N/A; College of Engineering; College of Engineering; College of Sciences; N/A; 179391; 27855The validation of a previously developed finite difference temperature prediction model is carried out for orthogonal machining process with a high precision infrared camera set-up, considering the temperature distribution in the tool. the thermal experiments are conducted with two different materials; al 7075, AISI 1050, with two different tool geometries; inserts having a rake angle of 6 degrees and 18 degrees, for different cutting velocities and feedrates. an infrared camera set-up is utilized for the thermal experiments. the results of the high precision infrared thermal measurements are compared with the outputs of the finite difference temperature model, considering the maximum and the mean temperatures in the tool-chip interface zone and the temperature distributions on the tool take face. the maximum tool-chip interface temperature increases with increasing cutting velocity and feedrate. the relationship between the maximum tool-chip interface temperature and the rake angle of the tool is not distinctive. the experimental results show good agreement with the simulations. (c) 2007 Elsevier B.V. all rights reserved.Publication Metadata only Efficient waveguide taper design with rapid and data-driven eigenmode expansion(Institute of Electrical and Electronics Engineers Inc., 2022) Department of Electrical and Electronics Engineering; N/A; Department of Physics; Mağden, Emir Salih; Oktay, Mehmet Can; Aydoğan, Aytuğ; Faculty Member; PhD Student; Student; Department of Electrical and Electronics Engineering; Department of Physics; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; 276368; N/A; N/AA novel, highly flexible, and data-driven method for designing compact and efficient integrated optical tapers will be discussed and demonstrated through state-of-the-art machine learning algorithms.Publication Metadata only Yağ mikrodamlacıklarının gliserol-su çözeltisinde hidrodinamik tuzaklanması(IEEE, 2014) Tanyeri, M.; N/A; Department of Physics; Department of Physics; Kayıllıoğlu, Oğuz; Erten, Ahmet Can; Kiraz, Alper; PhD Student; Teaching Faculty; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 233923; 22542We demonstrate a novel method for trapping and manipulating microdroplets in liquid media using a hydrodynamic trap. This method enables confinement and long-term observation of biological objects such as cells and macromolecules. / Mikrodamlacıkların sıvı içerisinde tuzaklanmasına ve hareket ettirilmesine olanak sağlayan yeni bir tuzaklama yöntemi sunuyoruz. Geliştirdiğimiz metot hücre ve biyolojik makromoleküllerin sıvı içerisinde tuzaklanması ve uzun süre gözlemlenmesini mümkün kılmaktadır.Publication Metadata only Optical sensor for humidity and hydrogen gas based on polymer microresonators(IEEE, 2016) Karadağ, Y.; Kılınç, N.; Department of Physics; N/A; N/A; Department of Physics; Department of Mechanical Engineering; Kiraz, Alper; Eryürek, Mustafa; Taşdemir, Zuhal; Anand, Suman; Alaca, Burhanettin Erdem; Faculty Member; PhD Student; PhD Student; Researcher; Faculty Member; Department of Physics; Department of Mechanical Engineering; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Science; College of Engineering; 22542; N/A; N/A; N/A; 115108Summary form only given. We report humidity and hydrogen sensors employing elastic polymer (SU-8) optical microresonators fabricated with photolithography. The sensing mechanism relies on monitoring the spectral shifts of the optical whispering gallery modes (WGMs) in the transmission spectra recorded from the microresonators. WGMs are excited through SU-8 waveguides in which a tunable laser light is coupled from an optical fiber.Publication Metadata only Investigating monolayer protein-protein binding using surface enhanced IR spectroscopy(IEEE, 2019) Korkmaz, Semih; Department of Physics; Ramazanoğlu, Serap Aksu; Faculty Member; Department of Physics; College of Sciences; 243745N/APublication 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 Femtosecond laser ablated tracks on smart surfaces for droplet manipulation applications(Institute of Electrical and Electronics Engineers (IEEE), 2018) Coskun, Umut Can; Morova, Yaǧız; Bozkurt, Asuman Asikoglu; Erten, Ahmet Can; Jonas, Alexandr; Aktürk, Selcuk; N/A; Department of Physics; Department of Physics; Rashid, Muhammed Zeeshan; Morova, Berna; Kiraz, Alper; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 22542In droplet based microfluidics, ability of controlling the motion of the droplets insidechips have great importance for the applications such guiding, sorting, mixing and dividing of liquid droplets. In this study, we fabricated hydrophilic microchannels inside the chips by femtosecond laser ablation technique in order to control droplet motion. The laser beam focused on PDMS converts the irradiated regions to hydrophilic by ablating the coating entirely from the surface. Droplets follow the tracks because of the difference in wettability of ablated region and PDMS surfaces together with the topographical profile of the ablated tracks. Within this study, we investigated the manipulation of three kind of liquid droplets (water/surfactant mixture, pure water and pure etylene glycol) along microchannels with depths of 1μm, 1.5μm and 2μm. We verified the experimental results with simulations and analyzed the trajectories of the moving droplets with the different wettability along the tracks of different depths. Our results showed that, while topographical effects play role in droplet guiding for 1.5μm and 2μm tracks, for the case of 1μm depth of channel, surface energy modifications cause the guiding rather than the topographical step on the surface. These results will pioneer for sorting applicaitons of different microdroplets mixed in the same microfluidic chip. / Damla temelli mikroakışkan sistemlerinde, damlaların yonga içerisindeki hareketlerinin kontrolü, yönlendirme, ayrıştırma, birleştirme ve bölme gibi uygulamalarda oldukça önemlidir. Bu çalışmada, damlaların hareketinin kontrolünü sağlamak için mikroakışkan yonga içerisinde hidrofilik mikrokanalları femtosaniye lazer ablasyon tekniği ile ürettik. Polydimethylsiloxane (PDMS) üzerine odakladığımız fs lazer hüzmesi uyarılan bölgeyi tamamen aşındırarak hidrofilik hale getirmektedir. Damlalar, aşındırılan hidrofilik bölge ile PDMS yüzeyi arasındaki ıslanabilirlik ve topografik farklılık sebebiyle bu kanallara eşlenerek ilerlemektedir. Bu çalışma kapsamında, üç farklı polar akışkandan (su/yüzey aktif madde karışımı, saf su ve saf etilen glikol) yağ içerisinde ürettiğimiz damlaların, 1μm, 1.5μm ve 2μm derinliklerine sahip işlenmiş mikrokanallar aracılığıyla yönlendirilmesini araştırdık. Deneysel olarak gerçekleştiridiğimiz çalışmaların sonuçlarını simülasyon değerleri ile karşılaştırdık ve farklı yapıdaki akışkan damlaların farklı derinliklerdeki kanallara sahip yongalardaki hareket yörüngelerini inceledik. Elde ettiğimiz sonuçlarla 1.5μm ve 2μm derinliğindeki kanallarda damlaların yönlendirilmesi hususunda kanal topografisinin etkili olduğunu, 1μm derinliğindeki kanallar için ise kanalın yüzeyde sahip olduğu derinlik yerine yüzey enerjisindeki değişimin etkili olduğunu gösterdik. Elde ettiğimiz bu sonuçlar, aynı yonga içerisinde bulunan farklı ıslanabilirlik özeliklerine sahip akışkanların ayrıştırılması gibi uygulamalara imkan sağlayacaktır.Publication Metadata only Image reconstruction in frequency space using sinusoidal illumination patterns(IEEE, 2020) Aydın, Musa; Department of Physics; N/A; N/A; Department of Physics; Kiraz, Alper; Uysallı, Yiğit; Özgönül, Ekin; Morova, Berna; Faculty Member; PhD Student; PhD Student; Researcher; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; 22542; N/A; N/A; N/AStructured Illumination Patterns is an imaging technique used in microscopic imaging to achieve super-resolution image by exceeding the diffraction limit. In microscopic imaging, the light projected onto the sample to be imaged is modulated into two dimensional sinusoidal illumination patterns and the raw image is obtained. By using this technique, the image reconstruction algorithm applied to the raw images in the frequency space is provided to increase the resolution of the final image up to two times. In this study, to obtain the high resolution target image, convolution multiplication of the structured illumination patterns with a test image is applied and a moire fringe pattern is formed as a result of this product. Next, the steps of the structured illumination microscopy technique algorithm are described. Finally, the algorithm for image reconstruction in frequency space has been developed and the results are shown.