Browsing by Author "Elahi, Parviz"

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Open Access
1.06μm-1.35μm coherent pulse generation by a synchronously-pumped phosphosilicate Raman fiber laser
(OSA, 2017) Elahi, Parviz; Makey, Ghaith; Turnalı, Ahmet; Tokel, Onur; İlday, Fatih Ömer
Summary form only given. Rare-earth-doped fiber lasers are attractive for microscopy and imaging applications and have developed over the past decades rapidly. They are unable to cover near-infra-red region entirely and therefore Raman and parametric process are promising for producing new wavelengths which are out of emission band of the current fiber lasers. Here, we demonstrate a synchronously-pumped Raman laser system for producing coherent signals spanning from 1.06 μm to 1.35 μm. The laser system comprises a passively-mode-locked oscillator, two stages of amplifier and a phosphosilicate Raman oscillator. The schematic of experimental setup is shown in Fig. 1(a). A mode locked oscillator operating at 37 MHz is using as a seed source. The output pulse duration and central wavelength are 6 ps and 1065 nm, respectively. 6 mW output from oscillator is launched to pre amplifier comprises 85-cm long Yb 401-PM pumped by a single mode diode through a PM wavelength division multiplexer (WDM). The power amplifier consists of a 3.5-m long Yb 1200-DC-PM with 6 μm core diameter and 125 μm cladding diameter pumped by a temperature stabilized, high power multimode diode laser via a multimode pump-signal combiner (MPC). A 30/70 coupler is employed for delivering pump signal at 1060 nm to the Raman oscillator comprises 4.2-m long ph-doped fiber. To synchronize pump and Raman and achieve coherent pulses, we adjust the length of cavity by a precise translation stage. By using proper filter inside the Raman cavity, different wavelengths are achieved.
Open Access
1.7-GHz intra-burst repetition rate Yb-fiber amplifier system
(IEEE, 2015) Kalaycıoğlu, Hamit; Elahi, Parviz; Kerse, Can; Akçaalan, Önder; İlday, F. Ömer
Material processing efficiency of ultrafast pulses increases dramatically with repetition rate of the pulses, if the conditions are adjusted correctly to avoid excessive plasma and particulate shielding. However, given that there is a minimum pulse energy requirement, continuous operation at high repetition rates can be detrimental due to too much average power leading to heat accumulation. Burst-mode operation of lasers, wherein the amplifier periodically produces a group of pulses (a burst), which are very closely spaced in time, avoids this problem. However, ultrafast burst-mode lasers are typically limited to several 100 MHz intra-burst repetition rates. While this is sufficient for most materials, metals with high thermal conductivity require higher repetition rates.
Open Access
3.5-W, 42-MHz, single-mode chirped pulse amplification fiber laser system at 1560 nm
(OSA, 2017) Elahi, Parviz; Li, Huihui; İlday, Fatih Ömer
There is much interest in the development of high power ultra-short fiber laser systems due to their significant properties and applications. Among them, Er-doped fiber lasers are showing more attention, especially in silicon processing and photovoltaic industries. Chirp pulse amplification (CPA) is the most common approach to establish high-power/high energy fiber lasers. Here, we demonstrate a CPA fiber laser system operating at 1560 nm. The system provides 3.5 W average output power at 42 MHZ pulse repetition rate corresponds to 83 nJ pulse energy. The laser system comprises a passively mode-locked oscillator and two amplifier stages, where the power amplifier is based on claddingpumped 10 μm-core EY co-doped fiber. The output pulses are compressible to 180 fs by using of two compressor gratings. The schematic of experimental setup is shown in Fig. 1(a). Seed source is a home-built dispersion-managed passively mode-locked oscillator delivering 5-ps long pulses at 42 MHZ repletion rate and 8 mW average power. We are using 70-cm long positive dispersion fiber (OFS, R2=56.7 fs2 /mm) after the gain fiber to manage group velocity dispersion delay (GDD) of the cavity and achieve broad spectrum. The output from oscillator delivers to stretch fiber including a 10-m long fiber (OFS). 30-ps long pulses after that delivers to the first stage amplifier, which consists of 1-m long Er 80-4/125 (CorActive) pumped by a single-mode diode laser at 976 nm via a wavelength-division-multiplexer (WDM). The first stage amplifier generates 120 mW of average power. The power amplifier is based on 1.4-m long Er-Yb co-doped fiber with 10 μm core and 128 μm cladding diameter. The pump source is a 16-W wavelength-stabilized diode laser at 976 nm. The pump and signal are combined with a multimode pump signal combiner (MPC). A 10/128 fiber pigtailed collimator is used to collimate output beam.
Open Access
3.5-W, femtosecond chirped pulse amplification fiber laser system at 1560 nm
(IEEE, 2017) Elahi, Parviz; Li, Huihui; İlday, Fatih Ömer
We report a single-mode, 42 MHz, 3.5-W average power chirped pulse amplification fiber laser system operating at 1560 nm. The laser system comprises a dispersion-managed mode-locked oscillator and twoamplifier stages. The output pulses are compressed to 180 fs by using two diffraction gratings.
Open Access
50-W, 1.6-GHz pulse repetition rate from a burst-mode Yb-doped fiber laser
(IEEE, 2017) Elahi, Parviz; Ertek, A. C.; Eken, K.; İlday, Fatih Ömer
We report a 50-W average power Yb-doped fiber laser amplifier system. The laser system produces bursts at a minimum rate of 200 kHz, with 1.6 GHz intraburst repetition rate. The total energy delivers in a burst is 250 μJ and the individual pulse energy is about 0.4 μJ. The output pulses are compressed to 270 fs by using two compressor gratings.
Open Access
Ablation-cooled material removal at high speed with femtosecond pulse bursts
(OSA, 2015) Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Akçaalan, Önder; Yavaş, S.; Aşık, M. D.; Kesim, Deniz Koray; Yavuz, Koray; Çetin, Barbaros; İlday, Fatih Ömer
We report exploitation of ablation cooling, a concept well-known in rocket design, to remove materials, including metals, silicon, hard and soft tissue. Exciting possibilities include ablation using sub-microjoule pulses with efficiencies of 100-mJ pulses.
Open Access
Applying the principle of orthogonality of high dimensional random vectors to obtain high-density, large-volume 3D holographic display
(OSA, 2018) Makey, Ghaith; Yavuz, Özgün; Kesim, Denizhan Koray; Turnalı, Ahmet; Elahi, Parviz; Toumi, J.; El-Daher, M. S.; Ilday, Serim; Tokel, Onur; İlday, F. Ömer
The efforts toward truly 3D displays are far from exploiting the full potential of holography. Here, we apply the principle of orthogonality of high dimensional random vectors to obtain unprecedented dense, large volume holograms.
Open Access
Breaking crosstalk limits to dynamic holography using orthogonality of high-dimensional random vectors
(Nature Publishing Group, 2019) Makey, Ghaith; Yavuz, Özgün; Kesim, Denizhan K.; Turnalı, Ahmet; Elahi, Parviz; İlday, Serim; Tokel, Onur; İlday, F. Ömer
Holography is the most promising route to true-to-life three-dimensional (3D) projections, but the incorporation of complex images with full depth control remains elusive. Digitally synthesized holograms1,2,3,4,5,6,7, which do not require real objects to create a hologram, offer the possibility of dynamic projection of 3D video8,9. Despite extensive efforts aimed at 3D holographic projection10,11,12,13,14,15,16,17, however, the available methods remain limited to creating images on a few planes10,11,12, over a narrow depth of field13,14 or with low resolution15,16,17. Truly 3D holography also requires full depth control and dynamic projection capabilities, which are hampered by high crosstalk9,18. The fundamental difficulty is in storing all the information necessary to depict a complex 3D image in the 2D form of a hologram without letting projections at different depths contaminate each other. Here, we solve this problem by pre-shaping the wavefronts to locally reduce Fresnel diffraction to Fourier holography, which allows the inclusion of random phase for each depth without altering the image projection at that particular depth, but eliminates crosstalk due to the near-orthogonality of large-dimensional random vectors. We demonstrate Fresnel holograms that form on-axis with full depth control without any crosstalk, producing large-volume, high-density, dynamic 3D projections with 1,000 image planes simultaneously, improving the state of the art12,17 for the number of simultaneously created planes by two orders of magnitude. Although our proof-of-principle experiments use spatial light modulators, our solution is applicable to all types of holographic media.
Open Access
Buried waveguides written deep inside silicon
(OSA, 2017) Turnalı, Ahmet; Tokel, Onur; Kesim, Denizhan Koray; Makey, Ghaith; Elahi, Parviz; İlday, Fatih Ömer
Summary form only given. Silicon waveguides are widely used as optical interconnects and they are particularly important for Si-photonics. Si-based devices, along with other optical elements, are entirely fabricated on the top surface of Si wafers. However, further integration of photonic and electronic devices in the same chip requires a new approach. One alternative is to utilize the bulk of the wafer for fabricating photonic elements. Recently, we reported a direct-laser-writing method that exploits nonlinear interactions and can generate subsurface modifications inside silicon without damaging the surface. Using this method, we fabricated several functional optical elements including gratings, lenses, and holograms. In this work, we demonstrate optical waveguides entirely embedded in Si.
Open Access
Compact 1.5-GHz intra-burst repetition rate Yb-doped all-PM-fiber laser system for ablation-cooled material removal
(OSA, 2017) Akçaalan, Önder; Kalaycıoğlu, Hamit; Elahi, Parviz; Deminskyi, Petro; İlday, Fatih Ömer
Summary form only given. Femtosecond (fs) laser pulse sources have become increasingly popular in the last decade as a result of their practical features, such as insensitivity to environmental variations, versatile designs, high power outputs. However, much of the progress is with non-integrated specialty fibers, which involve some compromise on these practical features. Monolithic fiber chirped pulse amplification (CPA) systems are very attractive for industrial and scientific applications due to the features such as compactness, reliability and robustness. Although fs fiber laser systems are powerful technologies for material and tissue processing, limited ablation rates and high energy are drawbacks. Recently, we identified a new regime of laser-material interaction, ablation cooled material removal [1], where the repetition rate has to be high enough so that the targeted spot size cannot cool down substantially by heat conduction which scales down ablation threshold by several orders of magnitude and reduces thermal effects to the bulk of the target. Here, we demonstrate a compact all-PM-fiber laser amplifier system with an intra-burst repetition rate of 1.5 GHz able to produce bursts ranging from 20-ns to 65-ns duration with 20 μJ to 80 μJ total energy, respectively, and pulses with up to 1 μJ individual energy at burst repetition rates ranging from 25 kHz to 200 kHz (Fig. 1(a)). The seed signal is generated by a home-built all-normal dispersion oscillator with a spectrum centered at 1035 nm and 20-nm (FWHM), 100 mW output and 385 MHz repetition rate (Fig. 1(b)). After the oscillator, rest of the system is built of polarization maintaining (PM) components and a single-mode pre-amplifier controls both dispersion and nonlinearity in the amplifier system. The pulses are stretched with a 110 m-long fiber after this pre-amplifier and raised to a repetition rate of 1.5 GHz by a multiplier. The signal is amplified again by a second single-mode pre-amplifier before converted into burst-mode via an acousto-optic modulator (AOM). Finally, a forward-pumped double-clad power amplifier, built of PM 10/125 Yb 1200 DC (nLight) fiber and pumped by a 18-W wavelength stabilized diode, boosts the optical power. To compress the pulses, a pair of 1200 line/mm transmission gratings is preferred to denser gratings to limit third order dispersion (TOD). Further, fiber lengths are shortened as much as possible to minimize nonlinear effects including Raman scattering and thus the power conversion efficiency is relatively low, around 20% for the power amplifier. The autocorrelation measurement for the compressed pulses indicates a width of ~250 fs (Fig. 1(d)). The amplified output spectrum of FWHM of 14 nm is shown in (Fig. 1(c)).
Open Access
Controlling active brownian particles in complex settings
(OSA, 2017) Velu, Sabareesh K. P.; Pinçe, Erçağ; Callegari, Agnese; Elahi, Parviz; Gigan, S.; Volpe, Giovanni; Volpe, G.
We show active Brownian particles (passive Brownian particles in a bacterial bath) switches between two long-term behaviors, i.e. gathering and dispersal of individuals, in response to the statistical properties of the underlying optical potential.
Open Access
Dissipative solitons generated from a mode-locked Raman laser
(IEEE, 2015) Teğin, Uğur; Elahi, Parviz; Şenel, Ç.; Ergeçen, Emre; İlday, F. Ömer
Stolen, et al. introduced synchronously pumped oscillators where gain was achieved through stimulated Raman scattering (SRS) as a method to reach wavelengths outside of the limited range covered by laser gain media [1]. Raman lasers are thus pumped by another laser source and generate a frequency-shifted Stokes (or anti Stokes) wave. Raman solitons which are generated by this technique typically require km-long cavities, require anomalous-dispersion fibers and are limited to low pulse energies [2]. Self-similarly evolving parabolic pulses have also been generated, but required km-long fibers and achieved 6 ps duration [3]. Here, we present a new type of Raman oscillator, which supports dissipative solitons, does not require anomalous dispersion and a km-long cavity.
Open Access
Generation of dissipative solitons in normal-dispersion Raman fiber laser
(IEEE, 2016) Teğin, Uğur; Elahi, Parviz; Şenel, Ç.; Ergeçen, E.; İlday, Fatih Ömer
Dissipative soliton pulses in a synchronously pumped all-normal-dispersion Raman fiber laser is presented theoretically and experimentally. The laser generates 7.1 nJ intra-cavity pulses at 1.12 μm and is compressed to 136 fs.
Open Access
High energy dissipative raman soliton laser through XPM stabilization
(Optical Society of America (OSA), 2015-10) Ergeçen, E.; Tegin, Uğur; Elahi, Parviz; Şenel, Ç.; İlday, F. Ömer
Dispersion, nonlinearity and gain determine the intracavity pulse behaviour. We show that pump depletion and XPM play a significant role in the stabilization of high energy dissipative Raman solitons. Using this theoretical knowledge, we predict and demonstrate 7-nJ femtosecond pulses at 1120 nm. © OSA 2015.
Embargo
High-precision laser focus positioning of rough surfaces by deep learning
(Elsevier Ltd, 2023-05-18) Polat, Can; Yapici, Gizem Nuran; Elahi, Sepehr; Elahi, Parviz
This work presents a precise positioning detection based on a convolutional neural network (CNN) to control the laser focus in laser material processing systems. The images of the diffraction patterns measured at different positions of the laser focus concerning the workpiece are classified in the range of the Rayleigh length of the focusing lens with an increment of about 7% of it. The experiment was carried out on different materials with different levels of surface roughness, such as copper, silicon, and steel, and over 99% accuracy in the positioning detection was achieved. Considering surface roughness and camera noise, a theoretical model is established, and the effects of these parameters on the accuracy of focus detection are also presented. The proposed method exhibits a noise-robust focus detection system and the potential for many precise positioning detection systems in industry and biology. © 2023 Elsevier Ltd.
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
Influence of modulation of pump and seed signals on fiber amplification of broadband pulses
(OSA, 2011) Gürel, Kutan; Elahi, Parviz; Budunoğlu, İbrahim Levent; Şenel, Çağrı; Paltani, Punya Prasanna; İlday, Fatih Ömer
We report on characterization of the transfer of pump and seed signal modulations, including noise, during fiber amplification. We demonstrate experimentally and theoretically that pump (signal) modulations are transferred only below (above) a cut-off frequency.
Open Access
Influence of pump noise on mode-locked fiber oscillators
(OSA, 2015) Teamir, Tesfay G.; Elahi, Parviz; Budunoğlu, İbrahim Levent; Gürel, Kutan; İlday, Fatih Ömer
Pump modulation transfer function (MTF), and its dependence on pump power are investigated for all normal dispersion, dispersion managed and soliton-like mode-locked oscillator both in experiment and simulation. We find that cavity losses and pulse instabilities such as multiple pulsing influence noise transfer, strongly.
Open Access
Intracavity optical trapping of microscopic particles in a ring-cavity fiber laser
(Nature Publishing Group, 2019-06) Kalantarifard, Fatemeh; Elahi, Parviz; Makey, Ghaith; İlday, F. Ömer; Volpe, Giovanni; Maragò, O. M.
Standard optical tweezers rely on optical forces arising when a focused laser beam interacts with a microscopic particle: scattering forces, pushing the particle along the beam direction, and gradient forces, attracting it towards the high-intensity focal spot. Importantly, the incoming laser beam is not affected by the particle position because the particle is outside the laser cavity. Here, we demonstrate that intracavity nonlinear feedback forces emerge when the particle is placed inside the optical cavity, resulting in orders-of-magnitude higher confinement along the three axes per unit laser intensity on the sample. This scheme allows trapping at very low numerical apertures and reduces the laser intensity to which the particle is exposed by two orders of magnitude compared to a standard 3D optical tweezers. These results are highly relevant for many applications requiring manipulation of samples that are subject to photodamage, such as in biophysics and nanosciences.
Open Access
Machine learning-based high-precision and real-time focus detection for laser material processing systems
(S P I E - International Society for Optical Engineering, 2022-05-17) Polat, Can; Yapıcı, Gizem Nuran; Elahi, Sepehr; Elahi, Parviz
This work explores a real-time and high precision focus finding for the ultrafast laser material processing for a different types of materials. Focus detection is essential for laser machining because an unfocused beam cannot affect the material and, at worst, a destructive effect. Here, we compare CNN and non-CNN-based approaches to focus detection, ultimately proposing a robust CNN model that can achieve high performance when only trained on a portion of the dataset. We use an ordinary lens (11 mm focal length, 0.25 NA) and a CMOS camera. Our robust CNN model achieved a focus prediction accuracy of 95% when identifying focus distances in -150, -140,...,0,...,150 µm, each step is about 7% of the Rayleigh length, and a high processing speed of 1000+ Hz on a CPU.