Browsing by Author "Pavlov, Ihor"

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Open Access
10 W, 10 ns, 50 kHz all-fiber laser at 1.55 µm
(Optical Society of America, 2012) Pavlov, Ihor; Dülgergil, E.; İlbey, Emrah; İlday, Fatih Ömer
We report on an all-fiber, singlemode MOPA system at 1.55 µm producing 10-ns, 200-µJ pulses with 20 kW of peak power and utilize it to micromachine crystalline Si, which is largely transparent at this wavelength.
Open Access
10-W, 156-MHz all-fiber-integrated Er-Yb-doped fiber laser-amplifier system
(Optical Society of America, 2012) Pavlov, Ihor; İlbey, Emrah; Dülgergil, Ebru; İlday, Fatih Ömer
We demonstrate all-fiber, high-power chirped-pulse-amplifier system, operating at 1550 nm. 156-MHz soliton oscillator seeds a two-stage single-mode amplifier with output power of 10 W. After external compression, pulse duration is 0.6 ps. © 2012 Optical Society of America.
Open Access
The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography
(Taylor and Francis, 2018) Pavlov, Ihor; Rybak, A.; Dobrovolskiy, A.; Kadan, V.; Blonskiy, I.; İlday, Fatih Ömer; Kazantseva, Z.; Gvozdovskyy, I.
It is well known that the alignment of liquid crystals (LCs) can be realised by rubbing or photoalignment technologies. Recently, nonlinear laser lithography (NLL) was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time, the usage of the NLL as a perspective method of the alignment of nematics was presented. By NLL, nanogrooves with about 0.92 μm period were formed on Ti layer. The nanostructured Ti layer (NSTL) was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of NSTLs were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy (AE) of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal AE, obtained for pure NSTL, is comparable with photoalignment technology. It was found that the deposition of polyimide film on NSTL leads to the gain effect of the azimuthal AE. Also, atomic force microscopy (AFM) study of aligning surfaces was carried out.
Open Access
Balancing gain narrowing with self phase modulation: 100-fs, 800-nJ from an all-fiber-integrated Yb amplifier
(IEEE, 2013) Pavlov, Ihor; Rybak, A.; Cenel, C.; İlday, F. Ömer
There is much progress in Yb-fiber oscillator-amplifier systems, which enable generation of high-repetition-rate, microjoule energies and sub-picosecond pulse widths [1,2]. Given the extremely large total gain factors to reach microjoules starting from nanojoules, which is often in the range of 40-60 dB, due to losses, and the impact of mismatched high-order dispersion as temporal stretching and compression of pulses by large factors (30-40 dB) need to be employed. As a result of these challenges, most of the Yb-fiber amplifiers have resulted in pulse durations of several 100 fs or longer. While pulse durations in this range are suited for some applications, there are many cases where 100-fs or shorter pulses in microjoule range are required. Gain narrowing can be effectively countered by self-phase modulation (SPM) [3] by limiting amplification factor in each stage of amplification and through careful optimization of SPM and inversion level along the gain fiber. The conceptual template is readily present in the evolution of the pulse inside the oscillator cavity, where gain factors are often in the 10-50 range per roundtrip. To the extend that the B-integral and the gain distribution along the amplifier can be kept identical to the oscillator by proper scaling of the chirped pulse width and fiber mode area, the original oscillator can be preserved in arbitrary number of amplification stages. Here, we demonstrate a highly fiber-integrated master-oscillator power-amplifier (MOPA) system, from which - 1 μJ pulses are extracted and externally compressed to 100 fs by arranging amplification in each stage as close as possible to the intra-cavity evolution. To our knowledge, these results are the shortest demonstrated from all-fiber-integrated amplifier at the microjoule level. © 2013 IEEE.
Open Access
Computer-generated holograms embedded in bulk silicon with nonlinear laser lithography
(IEEE, 2016) Turnalı, Ahmet; Tokel, Onur; Makey, Ghaith; Pavlov, Ihor; İlday, Fatih Ömer
Recently, we have showed a direct laser writing method to form subsurface structures inside silicon by exploiting nonlinear interactions. Here, we demonstrate utilization of this phenomenon to create computer-generated holograms buried in silicon.
Open Access
Controlling laser-induced self-organized patterns via engineered defects
(IEEE, 2015) Ergecen, E.; Yavuz, Özgün; Tokel, Onur; Pavlov, Ihor; Rızaoğlu, Anıl; İlday, F. Ömer
Nanoscale periodic surface structures are of paramount importance in material science [1]. The recently demonstrated Nonlinear Laser Lithography (NLL) technique allows creating nanostructure arrays over indefinitely large surfaces with remarkable periodicity, not attainable by conventional laser induced periodic surface structure (LIPSS) methods [2]. Using NLL with linearly polarized femtosecond pulses, nanolines parallel to polarization emerge from initial surface roughness, and propagate on the surface as the laser beam is scanned. Here, we demonstrate that the final surface patterns depend not only on the polarization, but also on the surface morphology, which is controllable by introducing artificial defects. We use line defects as a control parameter to select a surface tiling from a set of available ones.
Open Access
Direct laser writing of volume fresnel zone plates in silicon
(IEEE, 2015) Turnalı, Ahmet; Tokel, Onur; Pavlov, Ihor; İlday, F. Ömer
Functional optical elements fabricated on silicon (Si) constitute fundamental building blocks of Si photonics [1]. For the fabrication of these elements, conventional lithography and etching techniques are used. In spite of the success of these techniques, a functional optical element embedded inside silicon simply does not exist. Here, we present a maskless, one-step laser writing technique for creating phase-type Fresnel zone plates in the bulk of Si. Due to their effectiveness over a broad spectra, Fresnel zone plates (FZPs) are widely used in various micro-imaging applications [2]. Similar lenses have been fabricated inside silica [3,4], but are limited to the transparency window of silica. The silicon counterpart of these elements have been impossible to fabricate so far. By exploiting nonlinear absorption within the focal volume of a tightly focused laser, we generated permanent refractive index changes in Si. The imprinted high-index contrast was then used to fabricate a FZP inside Si. This three dimensional (3D) method can allow for alignment-free multilens systems. Moreover, using silicon as the lens material is fully CMOS compatible and applicable to silicon integrated optics, including single and array detectors.
Open Access
Doppler effect on nanopatterning with nonlinear laser lithography
(OSA, 2017) Yavuz, Özgün; Kara, Semih; Tokel, Onur; Pavlov, Ihor; İlday, Fatih Ömer
Summary form only given. Just five years after invention of the laser, laser induced periodic structures (LIPSS) had been reported. However, the structure period is not very uniform in LIPSS. Recently, with nonlinear laser lithography (NLL), long range ordered periodic surface structures had been maintained by exploiting various feedback mechanisms and nonlinearities. Albeit, fine tuning of structure period remains challenging. Here, we present an analogy between Doppler effect and structure period of the NLL which adds a capability of changing the structure period.
Open Access
Generation of 2-μ J 410-fs pulses from a single-mode chirped-pulse fiber laser operating at 1550 nm
(Springer Verlag, 2018) Pavlova, S.; Rezaei, Hossein; Pavlov, Ihor; Kalaycıoğlu, Hamit; İlday, Fatih Omer
We report on a simple, robust, femtosecond chirped-pulse-amplification system, based on Er- and Er-Yb-doped fibers, operating at a central wavelength of 1555 nm. The entire system is constructed from commercially available fiber components, except the grating compressor, for easy duplication by other researchers. The laser system produces chirped pulses with up to 4μJ of pulse energy at 250 kHz. After dechirping, the pulse duration is 410 fs and the pulse energy is reduced to 2μJ. The repetition rate of the laser is electronically tunable between 125 kHz and 60 MHz, limited by strong amplified spontaneous emission (ASE) generation at the low end. The amplifier system is almost completely fiber integrated, except for the pump delivery into the final amplifier stage, which is free-space backward-pumped to reduce undesired nonlinear effects, and the compressor which was designed using the gratings. The laser is practically free of misalignment and has exhibited excellent long-term stability during its use in various experiments for more than 600 working hours.
Open Access
Highly stable periodic structures using nonlinear laser lithography
(IEEE, 2016) Yavuz, Oğuzhan; Pavlov, Ihor; Tokel, Onur; Ergeçen, E.; Rızaoğlu, Anıl; İlday, Fatih Ömer
Nonlinear laser lithography (NLL) emerged as a novel surface structuring method allowing long-range periodic order. We present mathematical formalism for NLL, analysis of structure stability to perturbations and a way to control final tiling patterns.
Open Access
Holograms deep inside Silicon
(Optical Society of America, 2016) Makey, Ghaith; Tokel, Onur; Turnalı, Ahmet; Pavlov, Ihor; Elahi, Parviz; Yavuz, Ozg ¨ un; İlday, F. Ömer
Through the Nonlinear Laser Lithography method, we demonstrate the first computer generated holograms fabricated deep inside Silicon. Fourier and Fresnel holograms are fabricated buried inside Si wafers, and a generation algorithm is developed for hologram fabrication. © OSA 2016.
Open Access
Laser writing deep inside silicon for 3D information Processing
(IEEE, 2015) Tokel, Onur; Turnalı, Ahmet; Pavlov, Ihor; İlday, F. Ömer
Micromachining of silicon (Si) with lasers is being investigated since the 1970s [1]. So far, generation of controlled subsurface modification in the bulk of Si with high precision has not been achieved. This is highly desirable since successful integration of Si photonics and data transfer elements with conventional Si integrated circuits is proposed to lead to new generations of microprocessors [2,3]. Available techniques fabricate these optical and electronic elements on the top layer of the silicon-on-insulator platform. Despite the remarkable successes of conventional techniques, none of the available methods make use of the bulk of Si for positioning functional elements. Here, we report a method for photo-inducing deeply buried (down 1 mm) structures in Si wafers with pulsed infrared lasers. We demonstrate large aspect-ratio structures with 1-µm widths and long range order over millimetre scales. We further demonstrate multilevel spatial information encoding capabilities in subsurface barcodes.
Open Access
Laser-patterning stainless steel with nonlinear laser lithography for enhanced tribological properties
(IEEE, 2015) Gnilitskyi, I.; Pavlov, Ihor; Rotundo, F.; Orazi, L.; İlday, Serim; Martini, C.; İlday, F. Ömer
The production of nanostructures on different materials attracts much attention in different fields of manufacturing as a result of increased availability, affordability and technical capability of laser-based methods [1,2]. However, some shortcomings such as relatively low speed of processing, problems with material control, and lack of uniformity and/or repeatability over large areas continue to limit their practical adaptation.
Open Access
Laser-slicing of silicon with 3D nonlinear laser lithography
(OSA, 2017) Tokel, Onur; Turnalı, Ahmet; Çolakoğlu, T.; İlday, Serim; Borra, M. Z.; Pavlov, Ihor; Bek, A.; Turan, R.; İlday, Fatih Ömer
Recently, we have showed a direct laser writing method that exploits nonlinear interactions to form subsurface modifications in silicon. Here, we use the technique to demonstrate laser-slicing of silicon and its applications.
Open Access
Mathematical model of nonlinear laser lithography
(IEEE, 2015) Yavuz, Özgün; Ergecen, E.; Tokel, Onur; Pavlov, Ihor; İlday, F. Ömer
Laser induced periodic surface structures (LIPSS) had been observed just five years after the invention of laser [1]. Among the numerous LIPSS techniques none of them could maintain long-range order [2]. However, it has recently been demonstrated that long order periodic surface structures can be produced using nonlinear laser lithography (NLL) [3]. Here, we present a mathematical foundation for NLL.
Open Access
Nonlinear chirped-pulse amplification of a soliton-similariton laser to ~1 µJ at 1550 nm
(Optical Society of America, 2012) İlbey, Emrah; Pavlov, Ihor; Dülgergil, E.; Öktem, Bülent; Yavas, Seydi; Rybak, Andrii; Zhang, Zuxing; İlday, Fatih Ömer
We demonstrate all-fiber-integrated nonlinear CPA system operating at 1550 nm, seeded by a soliton-similariton laser. Chirped 2-μJ pulses are compressed to 700-fs, 0.5-μJ pulses at 1 MHz. Amplifier output is through a strictly singlemode fiber. © 2012 OSA.
Open Access
Nonlinear laser lithography for enhanced tribological properties
(IEEE, 2015-05) Gnilitskyi, I.; Pavlov, Ihor; Rotundo, F.; Orazi, L.; Martini, C.; İlday, Fatih Ömer
This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL). © 2015 OSA.
Open Access
Nonlinear laser lithography for photonic design of si solar cells
(IEEE, 2015) Pavlov, Ihor; Çolakoğlu, T.; Es, F.; Bek, A.; Turan, R.; Gnilitskyi, I.; İlday, F. Ömer
Nowadays Si-based solar cell (SC) remains the main source of solar energy in the world due to low cost of material and relatively simple, industrially acceptable technology. Despite of significant progress on increasing efficiency of these devices (the best laboratory samples demonstrated efficiency as much as 43.5%), for most of industrially manufactured SC’s the efficiency remains in the range of 10–18% [1]. A promising way to minimize thermodynamic losses for high efficiency Si-based photovoltaic devices, is photonic design of the device surfaces. The last one causes light trapping into the device, due to light interaction with micro- nano-structured surfaces, thus increasing effective light path interaction. However, the most of proposed methods for Si surface modification do not match industrial production requirements: such as fast manufacturing, environmental issues, and low cost per watt for final devices.
Open Access
Nonlinearity management: from fiber oscillators to amplifiers
(IEEE, 2016) İlday, Fatih Ömer; Şenel, Ç.; Hamid, R.; Teamir, Tesfay G.; Pavlov, Ihor; Teğin, Uğur; Ergeçen, E.; Elahi, Parviz; Iegorov, R.
While the standard approach to performance scaling in fiber lasers seeks to reduce nonlinear effects through chirping or mode scaling, I will review recent progress in a complementary approach, whereby the governing dynamics are meticulously exploited towards achieving superior performance.
Open Access
Optical waveguides written deep inside silicon by femtosecond laser
(OSA, 2017) Pavlov, Ihor; Tokel, Onur; Pavlova, S.; Kadan, V.; Makey, Ghaith; Turnalı, Ahmet; Çolakoğlu, T.; Yavuz, O.; İlday, Fatih Ömer
Summary form only given. Photonic devices that can guide, transfer or modulate light are highly desired in electronics and integrated silicon photonics. Through the nonlinear processes taking place during ultrafast laser-material interaction, laser light can impart permanent refractive index change in the bulk of materials, and thus enables the fabrication of different optical elements inside the material. However, due to strong multi-photon absorption of Si resulting delocalization of the light by free carriers induced plasma defocusing, the subsurface Si modification with femtosecond laser was not realized so far [1, 2]. Here, we demonstrate optical waveguides written deep inside silicon with a 1.5-μm high repetition rate femtosecond laser. Due to pulse-to-pulse heat accumulation for high repetition rate laser, additional thermal lensing prevents delocalization of the light around focal point, allowing the modification. The laser with 2-μJ pulse energy, 350-fs pulse width, operating at 250 kHz focused in Si produces permanent modifications. The position of the focal point inside of the sample is accurately controlled with pumpprobe imaging during processing. Optical waveguides of ~20-μm diameter, and up to 5.5-mm elongation are fabricated by translating the beam focal position along the optical axis. The waveguides are characterized with a 1.5-μm continuous-wave laser, through optical shadow-graphy (Fig. 1 a-b, e) and direct light coupling (Fig.1 c-d, f). The measured refractive index change obtained by quantitative shadow-graphy is ~6×10 -4 . The numerical aperture of the waveguide measured from decoupled light is 0.05.