Bulend Ortac
@bilkent.edu.tr
Bilkent University
RESEARCH INTERESTS
Laser, fiber optic, nanotechnology
Scopus Publications
Scopus Publications
Saliha Mutlu, Bülend Ortaç, Dogukan Hazar Ozbey, Engin Durgun, Sevil Savaskan Yılmaz, and Nergis Arsu
MDPI AG
In this study, we designed a platform based on a laser-driven approach for fast, efficient, and controllable MOF synthesis. The laser irradiation method was performed for the first time to synthesize Zn-based MOFs in record production time (approximately one hour) compared to all known MOF production methods with comparable morphology. In addition to well-known structural properties, we revealed that the obtained ZnMOFs have a novel optical response, including photoluminescence behavior in the visible range with nanosecond relaxation time, which is also supported by first-principles calculations. Additionally, photocatalytic degradation of methylene blue with ZnMOF was achieved, degrading the 10 ppm methylene blue (MB) solution 83% during 1 min of irradiation time. The application of laser technology can inspire the development of a novel and competent platform for a fast MOF fabrication process and extend the possible applications of MOFs to miniaturized optoelectronic and photonic devices.
Esra Kendir Tekgül and Bülend Ortaç
Elsevier BV
Timuçin Emre Tabaru, Ali Karatutlu, and Bülend Ortaç
Elsevier BV
Ali Aytac Seymen, Ezgi Gulten, Erol Ozgur, Bülend Ortaç, Irem Akdemir, Gule Cinar, Elif Mukime Saricaoglu, Gulen Guney-Esken, Erman Akkus, Fusun Can,et al.
Springer Science and Business Media LLC
AbstractCoronavirus Disease-19 (COVID-19) is a highly contagious infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The development of rapid antigen tests has contributed to easing the burden on healthcare and lifting restrictions by detecting infected individuals to help prevent further transmission of the virus. We developed a state-of-art rapid antigen testing system, named DIAGNOVIR, based on immune-fluorescence analysis, which can process and give the results in a minute. In our study, we assessed the performance of the DIAGNOVIR and compared the results with those of the qRT-PCR test. Our results demonstrated that the sensitivity and specificity of the DIAGNOVIR were 94% and 99.2%, respectively, with a 100% sensitivity and 96.97% specificity, among asymptomatic patients. In addition, DIAGNOVIR can detect SARS‑CoV‑2 with 100% sensitivity up to 5 days after symptom onset. We observed that the DIAGNOVIR Rapid Antigen Test’s limit of detection (LoD) was not significantly affected by the SARS‑CoV‑2 variants including Wuhan, alpha (B1.1.7), beta (B.1.351), delta (B.1.617.2) and omicron (B.1.1.529) variants, and LoD was calculated as 8 × 102, 6.81 × 101.5, 3.2 × 101.5, 1 × 103, and 1 × 103.5 TCID50/mL, respectively. Our results indicated that DIAGNOVIR can detect all SARS-CoV-2 variants in just seconds with higher sensitivity and specificity lower testing costs and decreased turnover time.
Leila Graini and Bülend Ortaç
Optica Publishing Group
We numerically investigated a nonlinear Kerr beam self-cleaning (KBSC) dynamics accompanied by self-similar propagation regimes, which leads to single-mode parabolic pulse reshaping and simultaneously high beam quality based on KBSC, for special distributions of initially excited modes in graded-index multimode fiber (GRIN-MMF). We coupled a Gaussian pulse at 1060 nm, with 100 fs duration, into GRIN-MMF supporting 10 modes that fall into four discrete mode groups. As a result, by using initial powers below the KBSC threshold reported in the literature, the output spatial beam evolves from a speckled pattern into a bell-shaped beam; hence, the generated parabolic pulse is mainly carried by the fundamental mode, which is boosted by the KBSC process. We also provide promising indications for KBSC on different higher-order modes.
Ali Karatutlu, Timuçin Emre Tabaru, and Bülend Ortaç
Wiley
Bülend Ortaç, Saliha Mutlu, Taylan Baskan, Sevil Savaskan Yilmaz, Ahmet Hakan Yilmaz, and Burcu Erol
MDPI AG
Thermally conductive phase-change materials (PCMs) were produced using the crosslinked Poly (Styrene-block-Ethylene Glycol Di Methyl Methacrylate) (PS-PEG DM) copolymer by employing boron nitride (BN)/lead oxide (PbO) nanoparticles. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) methods were used to research the phase transition temperatures, the phase-change enthalpies (melting enthalpy (ΔHm), and crystallization enthalpies (ΔHc)). The thermal conductivities (λ) of the PS-PEG/BN/PbO PCM nanocomposites were investigated. The λ value of PS-PEG/BN/PbO PCM nanocomposite containing BN 13 wt%, PbO 60.90 wt%, and PS-PEG 26.10 wt% was determined to be 18.874 W/(mK). The crystallization fraction (Fc) values of PS-PEG (1000), PS-PEG (1500), and PS-PEG (10,000) copolymers were 0.032, 0.034, and 0.063, respectively. XRD results of the PCM nanocomposites showed that the sharp diffraction peaks at 17.00 and 25.28 °C of the PS-PEG copolymer belonged to the PEG part. Since the PS-PEG/PbO and the PS-PEG/PbO/BN nanocomposites show remarkable thermal conductivity performance, they can be used as conductive polymer nanocomposites for effective heat dissipation in heat exchangers, power electronics, electric motors, generators, communication, and lighting equipment. At the same time, according to our results, PCM nanocomposites can be considered as heat storage materials in energy storage systems.
Oguzhan Karakurt, Eda Alemdar, Mert Can Erer, Duygu Cevher, Selin Gulmez, Umut Taylan, Sevki Can Cevher, Gonul Hizalan Ozsoy, Bulend Ortac, and Ali Cirpan
Elsevier BV
Pinar Beyazkilic, Samet Akcimen, Caglar Elbuken, Bülend Ortaç, Shengqiang Cai, and Emre Bukusoglu
Wiley
Targeted, on‐demand delivery has been of interest using materials responsive to environmental stimuli. A delivery technique based on precise release of aqueous microdroplets from a liquid crystal (LC) medium with contactless stimulation is presented. A nematic LC is doped with a photothermal dye that produces heat under near IR light exposure. The heat is used to overcome the elastic strains in the LC phase, promoting the release of initially entrapped water droplets to the neighboring aqueous solution. Designing the geometry of LC‐based emulsions and tuning the light intensity and position allows for manipulation of the release in two distinct modes defined as pulsated and continuous. In the pulsated mode, water droplets are released transiently from the casted water‐in‐LC emulsion layer based on sweeping by the moving isotropic‐nematic phase boundary controlled by light. In the continuous mode, water droplets are ejected continuously from a droplet‐shaped water‐in‐LC emulsion, due to a heating‐induced internal flow controlled by light. The droplet release by contactless stimulation is used for the on‐demand dosing of dopamine and its oxidizing reagent from isolated reservoirs to obtain an in situ reaction signal for a hydrogen peroxide assay. A new dual‐mode release system developed with photothermal LCs holds potential in drug release, controlled mixing, and photothermal therapy.
Esra Kendir Tekgül, Yakup Midilli, Hüseyin Can Çamiçi, Elif Yapar Yıldırım, Ali Karatutlu, and Bülend Ortaç
Springer Science and Business Media LLC
Leila Graini and Bülend Ortaç
Springer Science and Business Media LLC
Ali Karatutlu, Elif Yapar Yıldırım, Esra Kendir, Yakup Midilli, Samet Akçimen, and Bülend Ortaç
Elsevier BV
Zehra Merve Cinan, Burcu Erol, Taylan Baskan, Saliha Mutlu, Bülend Ortaç, Sevil Savaskan Yilmaz, and Ahmet Hakan Yilmaz
MDPI AG
In this work, gamma-ray shielding features of crosslinked polystyrene-b-polyethyleneglycol block copolymers (PS-b-PEG) blended with nanostructured selenium dioxide (SeO2) and boron nitride (BN) particles were studied. This research details several radiation shielding factors i.e., mass attenuation coefficient (μm), linear attenuation coefficient (μL), radiation protection efficiency (RPE), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP). The irradiation properties of our nanocomposites were investigated with rays from the 152Eu source (in the energy intervals from 121.780 keV to 1408.010 keV) in a high-purity germanium (HPGe) detector system, and analyzed with GammaVision software. Moreover, all radiation shielding factors were determined by theoretical calculus and compared with the experimental results. In addition, the morphological and thermal characterization of all nanocomposites was surveyed with various techniques i.e., nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Acceptable compatibility was revealed and observed in all nanocomposites between the experimental and theoretical results. The PS-b-PEG copolymer and nanostructured SeO2 and BN particles exerted a significant effect in enhancing the resistance of the nanocomposites, and the samples with high additive rates exhibited better resistance than the other nanocomposites. From the achieved outcomes, it can be deduced that our polymer-based nanocomposites can be utilized as a good choice in the gamma-irradiation-shielding discipline.
Bülend Ortaç, Deepak Jain, Rajan Jha, Jonathan Hu, and Bora Ung
Optica Publishing Group
“Invited” labels were added to the titles of two articles appearing in this feature issue [J. Opt. Soc. Am. B 38, F38 (2021)JOBPDE0740-322410.1364/JOSAB.434413; J. Opt. Soc. Am. B 38, F115 (2021)JOBPDE0740-322410.1364/JOSAB.437891].
Bülend Ortaç, Deepak Jain, Rajan Jha, Jonathan Hu, and Bora Ung
Optica Publishing Group
In this introduction, we provide an overview of the papers that were accepted for publication in the feature issue on specialty optical fiber modeling, fabrication, and characterization. A total of 22 papers were published in JOSA B. This feature issue presents cutting-edge research on specialty optical fibers and highlights recent developments in a new generation of optical fibers.
Leila Graini and Bülend Ortaç
MDPI AG
This paper aims to pave the way towards the demonstration of spatiotemporal similariton pulses’ evolution in passive multimode fibers with Raman amplification. We numerically present this issue in graded-index and step-index multimode fibers and provide a first look at the complex spatiotemporal dynamics of similariton pulses. The results showed that the similariton pulses could be generated in both multimode fibers. The temporal and spectral evolution of the pulses can be characterized as parabolic shapes with linear chirp and kW peak power. By compressing these, high-energy femtoseconds pulses can be obtained, starting initial picosecond pulses. A spatial beam profile could be preserved in both multimode fibers with the most energy coupled to the fundamental mode. Specifically, the similariton pulses’ generation with Raman amplification in a graded-index multimode fiber improves the spatial beam self-cleaning process under the different initial modes’ excitation. The observation of a new beam self-cleaning process is another attractor feature of propagation in graded-index multimode fibers.
Ali Karatutlu, Elif Yapar Yildirim, Esra Kendir, and Bulend Ortac
IEEE
Polarization Maintaining (PM) fibers can be produced in different ways in terms of their stress-birefringent geometric structures such as Panda-type, bow-tie and elliptical core [1] . These designs in principal function in the same way causing internal stress on the core and creating birefringence between two orthogonal (slow and fast) axes. In the typical Panda-type PM fibers, polarization extinction ratio (PER) is preserved over 30 dB along the slow axis and there is over ~ 10 dB difference between the fast and slow axes (Region 1 and Region 2, respectively, Fig. 1.b .). On the other hand, elliptical core PM fibers can be produced without boron-doped stress rods and thus they are easier to manufacture than the other two PM fibers with compatible birefringence values. Some of the applications require utilizing PM fiber components in order to developed environmentally-stable laser systems [2] , [3] . For these reasons, a specialty PM fiber structure may be needed in which the properties of both Panda-type and elliptical core geometry PM fibers can be used together.
Yakup Midilli, Gorkem Liman, Gokhan Demirel, and Bulend Ortac
IEEE
Cladding light stripper (CLS) is a key component for high power fiber laser systems to remove the unwanted light sources out of the system effectively. If they cannot be removed out of the system, the quality of the laser beam is affected severely. For that purpose, the fabrication of CLS has been investigated for years based on two main approaches. One of them is etching method [1] , [2] and the other one is the coating method [3] , [4] . The CLS fabrication based on the recoated polymer has a problem of power scaling whereas the other one is more fragile since the fiber is deformed even though they are more capable of handling power. However, in this work we present a new method to coat a special polymer material on top of the fiber with Chemical Vapor Deposition (CVD) method with a high precision level in the range of nm scale.
Bartu Simsek, Ozan Aktas, Ali Karatutlu, Ahmet Basaran, Elif Yapar Yildirim, Yakup Midilli, and Bulend Ortac
IEEE
Fiber lasers are one of the most preferred of today's efficient coherent light sources in many application areas with their advantages such as stability, compactness, robustness, diffraction-limited beam quality, large available bandwidth, tuneability, and independence from alignment [1] . With the technological and material-based advances in fiber laser, it has become possible to reach multikilowatt output powers. In high-power fiber lasers, cladding light power can reach more than hundreds of watts, this unwanted light may affect system performance and beam quality greatly. The unwanted cladding light can be produced by amplified spontaneous emission (ASE) which cannot guide in the core, signal loss at fiber core caused by excessive bending, unabsorbed pump light in the active medium and splicing loss of the junction points. The elimination process of unwanted cladding light for the high-power fiber amplifiers became an important issue [2] . There are several techniques to extract the unwanted cladding light from the fiber laser system such as surface texturization by using mechanical system and CO 2 laser ablation, chemical etching, soft metal coating and high index polymer coating [3] , [4] .
Yakup Midilli, Bartu Simsek, and Bulend Ortac
IEEE
Pump combiners have been utilized to combine the power of the pump diodes in the high power fiber laser oscillator and amplifier systems. The common way of the fabrication of the pump combiners with signal feed-through are fused taper fiber bundle (TFB) which is based on end pump technique in which the signal fiber are also tapered along with the pump fibers [1] . Therefore, with these type of combiners pumping can only be achieved in one direction; however, recently it has been demonstrated that counter-pumping or bi-directional pumping mechanisms allow the power scaling up with lower non-linear interaction thresholds such as Stimulated Raman Scattering and most recently and importantly Transverse Mode Instability (TMI), such an effect that reduces the beam quality of the laser beam drastically [2] . Alternative one to the end pumping technique making both counter and bi-directional pumping possible is side coupler technique in which the fiber core remains uninterrupted and pump fiber points can be increased more freely than the other one. The most popular side pump combiner fabrication technique is the direct fusion method due to the suitability for high power laser operation [3] , [4] . With this motivation, we have also intended to fabricate a side pump combiner for the first time on a photonic crystal fiber (PCF) in order to open a way to all-fiber monolithic systems with PCFs. For that purpose, we have used a home-made PCF having 45/360 µm core/cladding diameters respectively and a pump fiber having 130 µm cladding diameter. PCF has air holes with 12 µm diameters and a lattice constant of 25 µm and so the ratio of them would be, $\\frac{d}{\\Lambda } = 0.48$ before the CO 2 laser operation.
A. A. Seymen, E. Ozgur, Z. Soran-Erdem, and B. Ortac
Institute of Electrical and Electronics Engineers (IEEE)
Patch-clamp technique is the gold standard for cellular electrophysiological measurements, which is capable of measuring single ion transport events across the cell membrane. However, the measurement possesses significant complexities, and it requires a high level of expertise, while its experimental throughput is nevertheless considerably low. Here, we suggest and experimentally demonstrate a laser-assisted method for performing cellular electrophysiological measurements. Femtosecond laser pulses, coupled to an optical microscope, are used to form a sub-micrometer hole on a thin polymer membrane separating two electrodes, where a nearby cell is subsequently placed onto the hole by negative pressure. Afterwards, the cell is punctured using subsequent laser exposure, revealing the cell membrane over the hole for electrophysiological recording. This system could be used to increase the output amount of the electrophysiological measurements substantially.