Browsing by Author "Pavlov, I."

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Open Access
Diffraction-limited, 10-W, 5-ns, 100-kHz, all fiber laser at 1.55 um
(Optical Society of America, 2014-04-25) Pavlov, I.; Dulgergil, E.; Ilbey, E.; Ilday, F. O.
This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 mu m producing 5-ns, 100-mu J pulses. These pulses are generated at a 100 kHz repetition rate, corresponding to 10 W of average power. The seed source is a low-power, current-modulated, single-frequency, distributed feedback semiconductor laser. System output is obtained from a standard single-mode fiber (Corning SMF-28). Consequently, the beam is truly diffraction limited, which was independently proven by M-2 measurements. Further increase of peak power is limited by onset of significant spectral broadening due to nonlinear effects, primarily four-wave mixing. Numerical simulations based on six-level rate equations with full position-and time-dependence were developed to model propagation of pulses through the amplifier chain. This capability allows minimization of the amplified spontaneous emission, which can be directly measured using a fast acousto-optic modulator to gate the pulses. (C) 2014 Optical Society of America
Open Access
Femtosecond laser written waveguides deep inside silicon
(Optical Society of America, 2017) Pavlov, I.; Tokel, O.; Pavlova, S.; Kadan, V.; Makey, G.; Turnalı, A.; Yavuz, Ö.; Ilday, F. Ö.
Photonic devices that can guide, transfer, or modulate light are highly desired in electronics and integrated silicon (Si) photonics. Here, we demonstrate for the first time, to the best of our knowledge, the creation of optical waveguides deep inside Si using femtosecond pulses at a central wavelength of 1.5 μm. To this end, we use 350 fs long, 2 μJ pulses with a repetition rate of 250 kHz from an Er-doped fiber laser, which we focused inside Si to create permanent modifications of the crystal. The position of the beam is accurately controlled with pump-probe imaging during fabrication. Waveguides that were 5.5 mm in length and 20 μm in diameter were created by scanning the focal position along the beam propagation axis. The fabricated waveguides were characterized with a continuous-wave laser operating at 1.5 μm. The refractive index change inside the waveguide was measured with optical shadowgraphy, yielding a value of 6 × 10−4, and by direct light coupling and far-field imaging, yielding a value of 3.5 × 10−4. The formation mechanism of the modification is discussed.
Open Access
High-power-high-repetition-rate-single-mode Er-Yb-doped fiber laser system
(Optical Society of America, 2012) Pavlov, I.; Ilbey, E.; Dulgergil, E.; Bayri, A.; Ilday, F. O.
We demonstrate an all-fiber-integrated, high-power chirped-pulse-amplification system operating at 1550 nm. The seed source is a soliton fiber laser with 156 MHz repetition rate. Two-stage single mode amplifier provides an amplification of more than 40 dB without significant spontaneous amplified emission. The power amplifier is based on cladding-pumped 10 mu m-core Er-Yb co-doped fiber, the output of which was spliced into standard singlemode fiber. We obtain 10 W average power in a strictly singlemode operation. After dechirping with a grating compressor, near transform-limited, 450 fs-long pulses are obtained. The laser source exhibits excellent short and long-term intensity stability, with relative intensity noise measurements characterizing the short-term stability. (C) 2012 Optical Society of America
Open Access
In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon
(Nature Publishing Group, 2017) Tokel, O.; Turnalı, A.; Makey, G.; Elahi, P.; Çolakoǧlu, T.; Ergeçen E.; Yavuz, Ö.; Hübner R.; Borra, M. Z.; Pavlov, I.; Bek, A.; Turan, R.; Kesim, D. K.; Tozburun, S.; Ilday, S.; Ilday, F. Ö.
Silicon is an excellent material for microelectronics and integrated photonics 1-3, with untapped potential for mid-infrared optics 4 . Despite broad recognition of the importance of the third dimension 5,6, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements 7, electronic devices and better electronic-photonic integration are lacking 8 . Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-μm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface - that is, 'in-chip' - microstructures for microfluidic cooling of chips, vias, micro-electro-mechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances.
Open Access
LIPSS for SERS: Metal coated direct laser written periodic nanostructures for surface enhanced raman spectroscopy
(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-11-18) Erkızan, S. N.; İdikut, F.; Demirtaş, Ö.; Goodarzi, A.; Demir, Ahmet Kemal; Borra, M.; Pavlov, I.; Bek, A.
A novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is introduced which yields densely nanostructured surfaces utilizing laser-induced periodic surface structuring (LIPSS) of crystalline silicon (Si). Two different interaction regimes yield low spatial frequency (LSFL) and high spatial frequency (HSFL) LIPSS patterns. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50–70 nm thick Ag layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by LSFL and HSFL nature of the structure. The SERS substrates are found to be capable of detecting a Raman analyte down to 10−11 m. SERS performance of the Ag deposited substrates at 532, 660, and 785 nm excitation wavelengths is compared. Both LSFL and HSFL Si surfaces with 70 nm thick Ag are found to exhibit the strongest SERS under 660 nm excitation exhibiting Raman enhancement factors (EFs) as high as 109. The Raman EFs are calculated both by SERS spectra experimentally, and using finite-elements method simulation of the electric field enhancement where a good agreement is found.
Open Access
Nano patterning of AISI 316L stainless steel with nonlinear laser lithography: sliding under dry and oil-lubricated conditions
(Elsevier Ltd, 2016) Gnilitskyi, I.; Rotundo, F.; Martini, C.; Pavlov, I.; Ilday, S.; Vovk, E.; Ilday, F. Ö.; Orazi, L.
Femtosecond laser-based Nonlinear Laser Lithography (NLL) was applied to AISI 316L stainless steel, which requires surface modification to achieve satisfactory tribological behaviour. NLL advances over the well-known Laser Induced Periodic Surface Structures (LIPSS) in terms of uniformity and long-range order of high speeds, over large areas. A galvanometric scanner head was used for an high production rate. Dry and lubricated sliding tests, considering different orientations of the nanotexture showed that COF values after NLL treatment are significantly lower. In lubricated tests, COF values of NLL-treated surfaces are nearly half the values of untreated surfaces, whereas the difference further increases when measured in dry conditions, where the orientation of the surface texturing influences the results.
Open Access
NLL-Assisted Multilayer Graphene Patterning
(American Chemical Society, 2018) Kovalska, E.; Pavlov, I.; Deminskyi, P.; Baldycheva, A.; İlday, Fatih Ömer; Kocabas, C.
The range of applications of diverse graphene-based devices could be limited by insufficient surface reactivity, unsatisfied shaping, or null energy gap of graphene. Engineering the graphene structure by laser techniques can adjust the transport properties and the surface area of graphene, providing devices of different nature with a higher capacitance. Additionally, the created periodic potential and appearance of the active external/inner/edge surface centers determine the multifunctionality of the graphene surface and corresponding devices. Here, we report on the first implementation of nonlinear laser lithography (NLL) for multilayer graphene (MLG) structuring, which offers a low-cost, single-step, and high-speed nanofabrication process. The NLL relies on the employment of a high repetition rate femtosecond Yb fiber laser that provides generation of highly reproducible, robust, uniform, and periodic nanostructures over a large surface area (1 cm2/15 s). NLL allows one to obtain clearly predesigned patterned graphene structures without fabrication tolerances, which are caused by contacting mask contamination, polymer residuals, and direct laser exposure of the graphene layers. We represent regularly patterned MLG (p-MLG) obtained by the chemical vapor deposition method on an NLL-structured Ni foil. We also demonstrate tuning of chemical (wettability) and electro-optical (transmittance and sheet resistance) properties of p-MLG by laser power adjustments. In conclusion, we show the great promise of fabricated devices, namely, supercapacitors, and Li-ion batteries by using NLL-assisted graphene patterning. Our approach demonstrates a new avenue to pattern graphene for multifunctional device engineering in optics, photonics, and bioelectronics.
Open Access
Nonlinear laser lithography for indefinitely large-area nanostructuring with femtosecond pulses
(Nature publishing group, 2013) Öktem, B.; Pavlov, I.; Ilday, S.; Kalaycıoǧlu, H.; Rybak, A.; Yavaş, S.; Erdoǧan, M.; Ilday F. Ö.
Dynamical systems based on the interplay of nonlinear feedback mechanisms are ubiquitous in nature. Well-understood examples from photonics include mode locking and a broad class of fractal optics, including self-similarity. In addition to the fundamental interest in such systems, fascinating technical functionalities that are difficult or even impossible to achieve with linear systems can emerge naturally from them if the right control tools can be applied. Here, we demonstrate a method that exploits positive nonlocal feedback to initiate, and negative local feedback to regulate, the growth of ultrafast laser-induced metal-oxide nanostructures with unprecedented uniformity, at high speed, low cost and on non-planar or flexible surfaces. The nonlocal nature of the feedback allows us to stitch the nanostructures seamlessly, enabling coverage of indefinitely large areas with subnanometre uniformity in periodicity. We demonstrate our approach through the fabrication of titanium dioxide and tungsten oxide nanostructures, but it can also be extended to a large variety of other materials.
Open Access
Nonlinear laser lithography to control surface properties of stainless steel
(Elsevier BV, 2015) Orazi, L.; Gnilitskyi, I.; Pavlov, I.; Serro, A. P.; Ilday, S.; Ilday, F. O.
In the present work a novel method to improve the surface properties of stainless steel is presented and discussed. The method, based on the use of a high repetition rate femtosecond Yb fibre laser, permits generation of highly reproducible, robust, uniform and periodic nanoscale structures over a large surface area. The technique is characterized by high productivity, which, in its most simple form, does not require special environmental conditioning. Surface morphology is scrutinized through SEM and AFM analyses and wettability behaviour is investigated by means of the sessile drop method using distilled-deionized water. It is shown that optimization of process parameters promotes anisotropic wetting behaviour of the material surface.
Open Access
Slicing crystalline silicon wafer by deep subsurface laser processing and selective chemical etching
(Institute of Electrical and Electronics Engineers Inc., 2019) Borra, M. Z.; Nasser, H.; Çiftpınar, E. H.; Turnalı, Ahmet; Deminskyi, Petro; Çolakoğlu, T.; Tokel, Onur; İlday, Fatih Ömer; Pavlov, I.; Turan, R.; Bek, A.
In this work, we demonstrate use of laser-induced silicon slicing (LASIS) technique to fabricate crystalline silicon (c-Si) slices [1]. In LASIS method, a nanosecond-pulsed fiber laser operating at 1.55 μm wavelength, focused deep in Si subsurface induces structural modifications near the focal point due to multiphoton absorption. The raster scan of the focal position inside of the sample, positioned in cross-sectional plane with respect to laser beam, produces a quasi-2D modified Si region. The modified Si region is then etched by cupper nitrite (Cu(NO 3 ) 2 )-based selective chemical etchant which selectively targets the laser-modified regions. In order to achieve high etch rate, smooth and defect-free surface; different concentrations of etchant components and etch durations were investigated.