Selcuk Akturk

Istanbul Technical University, İstanbul, Istanbul, Turkey

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Publications (89)130.47 Total impact

  • Ramazan Sahin, Ergun Simsek, Selcuk Akturk
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    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.
    CLEO: Science and Innovations; 06/2014
  • Ramazan Sahin, Selcuk Akturk, Ergun Simsek
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    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.
    Applied Physics A 06/2014; · 1.69 Impact Factor
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    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.
    Journal of Cultural Heritage 05/2014; 15(3):258–265. · 1.18 Impact Factor
  • R. Sahin, E. Simsek, S. Akturk
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    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.
    Applied Physics Letters 01/2014; 104(5). · 3.79 Impact Factor
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    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.
    Applied Physics Letters 01/2014; 104(9):091123-091123-4. · 3.79 Impact Factor
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    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.
    Journal of Biomedical Optics 09/2013; 18(9):98003. · 2.88 Impact Factor
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    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.
    Applied Physics Letters 05/2013; 102(19). · 3.79 Impact Factor
  • R. Sahin, E. Simsek, S. Akturk
    The European Conference on Lasers and Electro-Optics; 05/2013
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    T. Ersoy, B. Yalizay, S. Akturk
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    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.
    Journal of Quantitative Spectroscopy and Radiative Transfer 12/2012; 113(18):2470–2475. · 2.38 Impact Factor
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    ABSTRACT: We report nanometer-scale fabrication on metal thin films using ablation by femtosecond laser pulses, with Bessel beam profiles. Choosing the laser fluence around ablation threshold allows control of the structure size below the diffraction limit. We show that using Bessel beams has several advantages. Bessel beams have focal spot sizes insensitive to longitudinal position, which significantly relaxes alignment constraints. Tighter foci are easier to generate, less costly, and less prone to aberrations. Scaling the method to shorter wavelengths, and hence increasing the resolution is also straightforward. By using the proposed method, we generate structures with resolution below 200 nm.
    Applied Physics Letters 01/2012; 100(3). · 3.79 Impact Factor
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    ABSTRACT: We present the first experimental evidence of anisotropic photosensitivity of an isotropic homogeneous medium under uniform illumination. Our experiments reveal fundamentally new type of light induced anisotropy originated from the hidden asymmetry of pulsed light beam with a finite tilt of intensity front. We anticipate that the observed phenomenon, which enables employing mutual orientation of a light polarization plane and pulse front tilt to control interaction of matter with ultrashort light pulses, will open new opportunities in material processing.
    Optics Express 10/2011; 19(21):20657-64. · 3.55 Impact Factor
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    ABSTRACT: of Airy beams in turbid media has not yet been explored comprehensively. In this study, propagation of Gaussian, Bessel and Airy beams in turbid media was investigated experimentally. In experiments, we used variable concentration intralipid emulsion as turbid media. Intralipid emulsion samples diluted in distilled water at different densities were prepared. The sample was placed in a quartz cuvette with 10 mm optical path. We investigated change of intensity and beam profile with varying density. We used a He-Ne laser as a coherent light source. Bessel beams were produced by a conical lens (axicon). In order to generate Airy beams, we used a special optical element presented
    05/2011;
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    ABSTRACT: We show that planar hollow waveguides can be used to compress pulses to few-cycles, in energy up-scalable manner. Controlling the beam size in the free direction allows stable compression without compromising the spatial mode quality.
    High Intensity Lasers and High Field Phenomena; 02/2011
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    Ergun Simsek, Selcuk Akturk
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    ABSTRACT: Precise ablation of metals using tightly focused femtosecond laser pulses with intensities close to the damage threshold can yield sub-wavelength, nanometer-sized holes or craters. These structures in metals can exhibit plasmonic effects, thereby affecting the interactions involved. We numerically simulate light propagation inside such holes and model the ablation process. We show that surface plasmon resonances can be excited at near-infrared and visible wavelengths. At resonance wavelengths, significant enhancement of aspect ratio is possible. Our results show that plasmonic effects are essential for the understanding of precision laser processing of metals, and they can be exploited to significantly enhance the performance of laser micro- and nano-machining. KeywordsLaser ablation–Micro- and nano-cavities–Surface plasmons–Plasmonic enhancement
    Plasmonics 01/2011; 6(4):767-772. · 2.43 Impact Factor
  • Berna Yalizay, Burak Soylu, Selcuk Akturk
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    ABSTRACT: We demonstrate an optical element for generation of accelerating Airy beams. The element is conveniently constructed by combination of positive and negative cylindrical lenses of matching radii of curvature. With proper choice of lens curvatures, the resulting surface profile closely follows a cubic polynomial. Passing a gaussian beam through this element and performing optical Fourier transform yields beam profiles close to the Airy function. Our experiments demonstrate parabolic propagation, or acceleration, of the resulting focal spots.
    Journal of the Optical Society of America A 10/2010; 27(10):2344-6. · 1.67 Impact Factor
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    Selcuk Akturk, Xun Gu, Pamela Bowlan, Rick Trebino
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    ABSTRACT: The electric field of an ultrashort laser pulse often fails to separate into a product of purely temporal and purely spatial factors. These so-called spatio-temporal couplings constitute a broad range of physical effects, which often become important in applications. In this review, we compile some recent experimental and theoretical work on the understanding, avoidance and applications of these effects. We first present a discussion of the characteristics of pulses containing spatio-temporal couplings, including their sources, a mathematical description and the interdependence of different couplings. We then review different experimental methods for their characterization. Finally, we describe different applications of spatio-temporal couplings and suggest further schemes for their exploitation and avoidance.
    Journal of optics 08/2010; · 1.99 Impact Factor
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    ABSTRACT: We study in detail the compression of high-energy ultrashort laser pulses to the few-cycle regime in gas-filled planar hollow waveguides. In this scheme, the laser beam is guided in only one transverse dimension, whereas the other dimension is free to adjust, allowing scalability to high pulse energies. We report on various practical aspects of the planar hollow waveguide compression scheme and characterize the dependence of the performance of the method on several experimental parameters: (i) we evaluate different materials for the construction of planar waveguides; (ii) we investigate the dependence of the pulse duration on gas type and pressure; (iii) we measure the spatial intensity and phase; (iv) we characterize the pulse duration along the transverse beam direction; and (v) we investigate the focusability. An output pulse energy of 10.6 mJ at a duration of 10.1 fs (FWHM) in the beam center after compression is demonstrated. A careful estimation reveals that the radiation should be focusable to a relativistic intensity exceeding 1019 W cm−2 in the few-cycle regime. The experimental results are supported by numerical modeling of nonlinear pulse propagation inside planar hollow waveguides. We discuss energy up-scalability exceeding the 100 mJ level.
    New Journal of Physics 07/2010; 12(7):073015. · 4.06 Impact Factor
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    ABSTRACT: Femtosecond laser writing in glass is controlled by the polarization plane azimuth and intensity front tilt of light pulse. Polarization dependent distribution of extraordinary modifications along the light propagation direction is observed.
    05/2010;
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    ABSTRACT: Short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse. Electrons initially ionized from oxygen molecules and subsequently captured by neutral oxygen molecules provide the long-lived reservoir of low affinity allowing this process. A Bessel-like nanosecond-duration laser beam can easily detach these weakly bound electrons and multiply them in an avalanche process. We have experimentally demonstrated such revivals over a channel length of 50 cm by focusing the nanosecond laser with an axicon.
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    ABSTRACT: Short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse. Electrons initially ionized from oxygen molecules and subsequently captured by neutral oxygen molecules provide the long-lived reservoir of low affinity allowing this process. A Bessel-like nanosecond-duration laser beam can easily detach these weakly bound electrons and multiply them in an avalanche process. We have experimentally demonstrated such revivals over a channel length of 50 cm by focusing the nanosecond laser with an axicon.
    Optics Express 08/2009; 17(14):11450-6. · 3.55 Impact Factor

Publication Stats

671 Citations
130.47 Total Impact Points

Institutions

  • 2009–2014
    • Istanbul Technical University
      • Department of Electrical Engineering
      İstanbul, Istanbul, Turkey
  • 2013
    • Bogazici University
      • Institute of Biomedical Engineering
      İstanbul, Istanbul, Turkey
  • 2007–2009
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2008
    • ENSTA Bretagne
      Brest, Brittany, France
  • 2004–2007
    • Georgia Institute of Technology
      • School of Physics
      Atlanta, GA, United States