Selcuk Akturk

Istanbul Technical University, İstanbul, Istanbul, Turkey

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Publications (111)

  • Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We discussed two main approaches for generation of nanometer-scale structures using pulsed lasers. In the first, a bulk material is ablated in vacuum, gas or liquid and consequent re-solidification of the evaporated material in clusters generate the desired nanoparticles. While one can play with various experimental parameters (laser powers, type of liquids, background gas etc.) to control particle sizes, there is always a relatively broad distribution of particle sizes. Nevertheless, particles with sizes down to few nanometers are achievable. In the second approach, fs lasers are used to pattern material surfaces. This process is more controlled in the sense that the desired geometries are generated by scanning of the sample. On the other hand, best achievable resolutions are worse as compared to the former approach. Resolutions better than 100 nm over large surfaces is very difficult. Finally, special beam shaping methods forms an interesting frontier in pushing forward the fs laser nanomachining methods towards broader practical uses.
    Chapter · Jan 2016
  • Ceren Altıngöz · Berna Yalızay · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources.
    Article · Sep 2015 · Journal of the Optical Society of America A
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    Berna Yalizay · Yagiz Morova · Koray Dincer · [...] · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We report on the fabrication and characterization of versatile light waveguides exploiting filaments of a polar liquid confined within hydrophobic silica aerogels. Aerogels are highly porous materials with extremely low refractive index which makes them suitable as rigid cladding of liquid-core optofluidic waveguides based on total internal reflection of light. In this article, we introduce a new microfabrication technique that allows direct and precise processing of monolithic silica aerogels by ablation with femtosecond laser pulses. Using fast scanning of the focused laser ablation beam synchronized with the motion of the processed aerogel sample, we created high-quality straight microchannels of ∼5 mm length with controlled cross-sections inside monolithic aerogels. After the ablation, we filled the channels with high-refractive index ethylene glycol, forming multimode liquid core – solid cladding optofluidic waveguides. Subsequently, we carried out light-guiding experiments to measure overall optical attenuation of these waveguides. The characterization of waveguide transmission yielded values of propagation losses lower than , demonstrating that the liquid-core waveguides with laser-ablated aerogel cladding represent an attractive alternative in optofluidic applications targeting controlled routing of light along arbitrary three-dimensional paths.
    Full-text Article · Sep 2015 · Optical Materials
  • Tansu Ersoy · Çetin Yaman · Mehmet Uguryol · [...] · Selcuk Akturk
    Conference Paper · Jun 2015
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    C L Arnold · S Akturk · A Mysyrowicz · [...] · P Di Trapani
    [Show abstract] [Hide abstract] ABSTRACT: We investigate experimentally and numerically the nonlinear propagation of intense Bessel– Gauss vortices in transparent solids. We show that nonlinear Bessel–Gauss vortices preserve all properties of nonlinear Bessel–Gauss beams while their helicity provides an additional control parameter for single-shot precision micro structuring of transparent solids. For sufficiently large cone angle, a stable hollow tube of intense light is formed, generating a plasma channel whose radius and density are increasing with helicity and cone angle, respectively. We assess the potential of intense Bessel vortices for applications based on the generation of hollow plasma channels.
    Full-text Article · May 2015 · Journal of Physics B Atomic Molecular and Optical Physics
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    C L Arnold · Selcuk Akturk · André Mysyrowicz · [...] · Paolo Di Trapani
    [Show abstract] [Hide abstract] ABSTRACT: We investigate experimentally and numerically the nonlinear propagation of intense Bessel– Gauss vortices in transparent solids. We show that nonlinear Bessel–Gauss vortices preserve all properties of nonlinear Bessel–Gauss beams while their helicity provides an additional control parameter for single-shot precision micro structuring of transparent solids. For sufficiently large cone angle, a stable hollow tube of intense light is formed, generating a plasma channel whose radius and density are increasing with helicity and cone angle, respectively. We assess the potential of intense Bessel vortices for applications based on the generation of hollow plasma channels.
    Full-text Article · Apr 2015
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    B. Yalizay · Y. Morova · Y. Ozbakir · [...] · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We present a new method to form liquid-core optofluidic waveguides inside hydrophobic silica aerogels. Due to their unique material properties, aerogels are very attractive for a wide variety of applications; however, it is very challenging to process them with traditional methods such as milling, drilling, or cutting because of their fragile structure. Therefore, there is a need to develop alternative processes for formation of complex structures within the aerogels without damaging the material. In our study, we used focused femtosecond laser pulses for high-precision ablation of hydrophobic silica aerogels. During the ablation, we directed the laser beam with a galvo-mirror system and, subsequently, focused the beam through a scanning lens on the surface of bulk aerogel which was placed on a three-axis translation stage. We succeeded in obtaining high-quality linear microchannels inside aerogel monoliths by synchronizing the motion of the galvo-mirror scanner and the translation stage. Upon ablation, we created multimode liquid-core optical waveguides by filling the empty channels inside low-refractive index aerogel blocks with highrefractive index ethylene glycol. In order to demonstrate light guiding and measure optical attenuation of these waveguides, we coupled light into the waveguides with an optical fiber and measured the intensity of transmitted light as a function of the propagation distance inside the channel. The measured propagation losses of 9.9 dB/cm demonstrate the potential of aerogel-based waveguides for efficient routing of light in optofluidic lightwave circuits.
    Full-text Article · Feb 2015 · Proceedings of SPIE - The International Society for Optical Engineering
  • Ramazan Sahin · Tansu Ersoy · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: Femtosecond lasers can provide submicron ablation resolution, making them suitable and attractive for various micro/nanofabrication applications. Laser beam shaping lends further advantages and increases the versatility of these sources. In this work, we report on the use of femtosecond laser pulses with first-order Bessel function (Bessel vortex) beam profiles in ablation of metal thin films. The diffraction-free nature of Bessel beams provides significant convenience regarding alignment and repeatability. Ablation profiles with Bessel vortex beams generally consist of single or multiple concentric rings, determined by pulse fluence on target. We investigate single-pulse ablation behavior with two laser wavelengths (1,030 and 515 nm) and three different Bessel beam cone angles. For each case, we measure inner and outer ring diameters and compare our results with theoretical calculations.
    Article · Oct 2014 · Applied Physics A
  • Article · Oct 2014
  • Ramazan Sahin · Yagiz Morova · Ergun Simsek · Selcuk Akturk
    Conference Paper · Jul 2014
  • Ramazan Sahin · Ergun Simsek · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We report nanometer-size patterning of various thin films by femtosecond pulsed Bessel beams. Nanoslit arrays fabricated on gold films exhibit excitation of surface plasmon polaritons. We extend the approach to single-atomic-layer systems such as graphene.
    Conference Paper · Jun 2014
  • Ramazan Sahin · Selcuk Akturk · Ergun Simsek
    [Show abstract] [Hide abstract] ABSTRACT: The influence of beam intensity on laser ablation quality and ablation size is experimentally studied on graphene-coated silicon/silicon dioxide substrates. With an amplified femtosecond-pulsed laser system, by systematically decreasing the average power, periodic stripes with decreasing widths are ablated. Histogram analyses of the untouched and ablated regions of scanning electron microscope images of the fabricated structures make it possible to quantify the ablation quality. These analyses reveal that submicron ablation can be achieved while maintaining 75 % ablation accuracy by adjusting the beam intensity around the ablation threshold.
    Article · Jun 2014 · Applied Physics A
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    Tansu Ersoy · Tugba Tunay · Mehmet Uğuryol · [...] · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: Lasers have served as cleaning tools for historical objects and artworks for about 40 years. In many cases, superior results of laser cleaning were achieved with respect to traditional methods. In this technique, contaminations on the surface of the object are ablated by laser irradiation. In order to apply laser cleaning method to fragile materials such as paper made of cellulose or parchment, heat deposition to the bulk should be minimal, to prevent damage. In this work, it is demonstrated that laser pulses with femtosecond (fs) duration can exhibit non-thermal ablation of contaminants on paper samples. In particular, laser cleaning studies are concentrated on paper samples with sizing. Fs laser cleaning is performed on artificially soiled and aged samples, as well as on historical ones. The laser used in the experiments has pulse duration of 550 fs and 1030 nm center wavelength. The fluence of the laser is varied and the post-cleaning statuses of samples are investigated. The analyses are color changes, fiber integrity, chemical composition changes and mechanical strengths. These results show that fs lasers can be very efficient in cleaning paper samples, yielding minimal discoloration and no damage to fibers distinguishable on microscopic examination. The presence of sizing also provides further protection against possible side effects.
    Full-text Article · May 2014 · Journal of Cultural Heritage
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    Alexandr Jonas · Berna Yalizay · Selcuk Akturk · Alper Kiraz
    [Show abstract] [Hide abstract] ABSTRACT: We report on the preparation and characterization of free-standing optofluidic waveguides created on solid superhydrophobic (SH) substrates with patterned wetting properties. In order to locally modify the liquid-solid contact angle, we employed selective laser ablation of SH layers deposited on magnesium-fluoride substrates with low refractive index. Upon ablation, surfaces with hydrophilic channels surrounded by SH areas were obtained. Subsequently, we created liquid optical waveguides based on total internal reflection using ethylene glycol, a polar liquid with high refractive index spreading spontaneously along the hydrophilic surface channels. We evaluated the light guiding performance and losses of these optofluidic waveguides.
    Full-text Article · Mar 2014 · Applied Physics Letters
  • R. Sahin · E. Simsek · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We report on nanometer-scale patterning of single layer graphene on SiO2/Si substrate through femtosecond laser ablation. The pulse fluence is adjusted around the single-pulse ablation threshold of graphene. It is shown that, even though both SiO2 and Si have more absorption in the linear regime compared to graphene, the substrate can be kept intact during the process. This is achieved by scanning the sample under laser illumination at speeds yielding a few numbers of overlapping pulses at a certain point, thereby effectively shielding the substrate. By adjusting laser fluence and translation speed, 400 nm wide ablation channels could be achieved over 100 μm length. Raster scanning of the sample yields well-ordered periodic structures, provided that sufficient gap is left between channels. Nanoscale patterning of graphene without substrate damage is verified with Scanning Electron Microscope and Raman studies.
    Article · Jan 2014 · Applied Physics Letters
  • Ayse Sena Kabas · Tansu Ersoy · Murat Gülsoy · Selcuk Akturk
    [Show abstract] [Hide abstract] ABSTRACT: The aim is to investigate femtosecond laser ablation as an alternative method for enamel etching used before bonding orthodontic brackets. A focused laser beam is scanned over enamel within the area of bonding in a saw tooth pattern with a varying number of lines. After patterning, ceramic brackets are bonded and bonding quality of the proposed technique is measured by a universal testing machine. The results are compared to the conventional acid etching method. Results show that bonding strength is a function of laser average power and the density of the ablated lines. Intrapulpal temperature changes are also recorded and observed minimal effects are observed. Enamel surface of the samples is investigated microscopically and no signs of damage or cracking are observed. In conclusion, femtosecond laser exposure on enamel surface yields controllable patterns that provide efficient bonding strength with less removal of dental tissue than conventional acid-etching technique.
    Article · Sep 2013 · Journal of Biomedical Optics
  • R. Sahin · Y. Morova · E. Simsek · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: Nanoslit arrays are fabricated on thin metal film coated glass slides using femtosecond laser pulses with Bessel beam profiles. The optical properties of the fabricated structures with different periodicities are characterized with transmission spectroscopy. Experimental results reveal the existence of two separate surface plasmon resonance modes occurring at the metal-air and metal-glass interfaces. These two resonance modes cause two minima in the high transmission spectra of the sub-skin depth thick thin films in the visible and near infrared regions. The existence of double surface plasmon resonance modes is verified with additional experiments, theoretical and numerical studies. Due to its relaxed alignment constraints, reduced aberrations, scalability property to shorter wavelengths, and resulting shorter dimensions, nanofabrication with diffraction-free Bessel beams is an easy, cheap, and advantageous alternative to regular lithography techniques to fabricate nanoslit arrays. The shift of the resonance wavelength with a change in the refractive index of the surrounding medium can be exploited for enhanced sensing.
    Article · May 2013 · Applied Physics Letters
  • R. Sahin · E. Simsek · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: Femtosecond laser ablation with Bessel beam profile can yield high quality structures on metal thin films at nanoscale [1]. By adjusting the laser fluence one can control size of ablated structures. Moreover, resolution can go beyond the diffraction limit when the laser energy is adjusted around the ablation threshold [2]. Advantages of using diffraction-free Bessel beams bring us to ablate 125 nm-wide stripes. In this work, we demonstrate potential of Bessel-beam nanofabrication method and optical properties of created structures for plasmonic applications. Nanoslit arrays are structured through ablation by femtosecond laser with Bessel Beams on 25 nm-thick Gold (Au) film evaporated on Fused Silica substrate. We fabricated stripes at nanoscales with different periodicities (p=500 nm, 790 nm and 810 nm). Since the fabrication method does not require high cost focusing optics or any special sample preparation, process is straightforward and well candidate to compete against standard lithographical methods.
    Conference Paper · May 2013
  • T. Ersoy · B. Yalizay · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We experimentally investigate propagation of laser beams with different intensity profiles in highly scattering media. We generate transverse laser amplitude profiles with Gaussian, Bessel and Airy function envelopes. We then propagate these beams through optical phantoms formed with variable density intralipid solutions. At the sample exit, we compare change in maximum intensities, as well as beam profile reconstruction. We show that self-reconstruction properties of Bessel and Airy beams bring about slower decrease in maximum intensity with increasing scatterer density. On the other hand, the beam profiles deteriorate faster, as compared to reference Gaussian beams. Slower decrease in the intensity can be attributed to the wavevector spectra providing a continuous flow of energy to the beam center, while beam deterioration is linked to total beam volume in the scattering medium. These results show that beam shaping methods can significantly enhance delivery of intense light deeper into turbid media, but this enhancement is compromised by stronger speckling of beam profiles.
    Article · Dec 2012 · Journal of Quantitative Spectroscopy and Radiative Transfer
  • A. K. Türkoğlu · T. Ersoy · F. Canbaz · S. Akturk
    [Show abstract] [Hide abstract] ABSTRACT: We investigate the dynamics of femtosecond-laser drilling of metals, both theoretically and experimentally, by taking into account waveguide-like behavior of ablated cavities. In particular, we show that cylindrical holes generated during laser ablation of metals act like hollow optical waveguides. Since the drilling is generally achieved by a large number of consecutive pulses, each pulse is first guided through the channel formed by the previous pulses, and at the end of the channel, it is absorbed by the metal, making its own contribution to ablation. The ablation stops at maximum depth when attenuation in the cavity reduces the pulse fluence to the ablation threshold. We use waveguide theory to calculate attenuation constants, and perform an iterative calculation to model pulse-by-pulse ablation. We also performed detailed experiments and compare the results with the theoretical findings. When only absorption losses are included, the waveguide model predicts significantly deeper structures. On the other hand, when we include scattering losses caused by nanostructures formed on the cavity walls, quantitative agreement with experiments is achieved. The waveguide model is particularly effective at fluences close to ablation threshold, and it can explain several behaviors such as evolution of the depth per pulse and effect of the incoming pulse energy in different focusing configurations.
    Article · Sep 2012 · Applied Physics A

Publication Stats

1k Citations


  • 2012-2014
    • Istanbul Technical University
      • Department of Physics Engineering
      İstanbul, Istanbul, Turkey
  • 2005
    • Georgia Institute of Technology
      • School of Physics
      Atlanta, GA, United States