Browsing by Subject "Ultrafast optics"
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Item Open Access All-fiber low-noise high-power femtosecond Yb-fiber amplifier system seeded by an all-normal dispersion fiber oscillator(Institute of Electrical and Electronics Engineers, 2009) Mukhopadhyay, P.K.; Özgören, K.; Budunoğlu, I. L.; İlday, F. Ö.We report an all-fiber, high-power, low-noise amplifier system seeded by an all-normal-dispersion-mode-locked Yb-doped fiber laser oscillator. Up to 10.6 W of average power is obtained at a repetition rate of 43 MHz with diffraction-limited beam quality. Amplified pulses are dechirped to sub-160-fs duration in a grating compressor. It is to our knowledge the first high-power source of femtosecond pulses with completely fiber-integrated amplification comprising commercially available components. Long-term stability is excellent. Short-term stability is characterized and an integrated laser intensity noise of $$0.2% is reported. We also conclude that all-normal dispersion fiber oscillators are low-noise sources, suitable as seed for fiber amplifiers. Detailed numerical modeling of both pulse generation in the oscillator and propagation in the amplifier provide very good agreement with the experiments and allow us to identify its limitations. © 2006 IEEE.Item Open Access Collective pulse amplification in burst mode fiber laser amplifiers in gain-managed nonlinearity regime(Bilkent University, 2023-08) Maghsoudi, AmirhosseinUltrafast lasers have diverse applications, ranging from optical metrology and spectroscopy to microscopy. Outside of the research laboratory, the most important application continues to be material processing, particularly precision micromachining. In traditional ultrafast processing, high-energy pulses at low repetition rates are used. The recently introduced ablation-cooled regime achieves greater speeds and material removal efficiencies through the use of moderate-energy pulses at much higher repetition rates. However, higher repetition rates also demand short pulses, and higher speeds require higher average powers, such as sub-50 fs pulses at kilowatt average powers. Such parameters are far beyond the current state of the art, but there appears to be no fundamental reason such performance could not be achieved. One common approach to exploit the ablation-cooled regime is to utilized bursts, or groups of pulses. However, such burst-mode amplifiers have resulted in relatively pulse durations to date. This thesis aims to overcome this limitation by implementing burst-mode operation in another recently discovered regime, namely, that of gain-managed nonlinear amplification. In ultrafast laser material processing, sub-50 femtosecond pulse widths and kW average powers are desirable. However, such lasers have yet to be reported in the literature due to the complexity of such systems. For obtaining sub-50 femtosecond pulses, the pulse evolution needs to be well-engineered. Additionally, kW average powers require active cooling systems. A practical method to decrease the average powers in the laser systems yet achieve the same pulse energies is to amplify bursts of pulses instead of a continuous stream of them. These bursts allow the energy to be more confined in time and the average power to be lower. In the no-burst case, various nonlinear pulse amplification regimes aid the design processes and produce high-quality pulses. One such regime is the gain-managed nonlinearity, observed after shifting the gain spectrum towards longer wavelengths accompanied by nonlinear spectral broadening. This process results in very broad optical spectra and short pulses for the amplified pulses. Obtaining sub-50 fs pulses in the continuous case is often complicated, and the results are hard to reproduce. However, with the gain-managed nonlinearity regime, sub-50 femtosecond pulses can be routinely obtained by correctly choosing the amplifier parameters. Despite that, with the inclusion of bursts, pulse parameters tend to be much worse, mainly due to having non-uniform pulses within a burst. Hence, obtaining sub-50 femtosecond pulses in burst-mode lasers is very challenging, and so far, no such lasers have been reported. Combining this regime with continuously pumped signal burst lasers, we have obtained pulses with 900 nJ energies and sub-50 femtosecond pulse widths with pulse repetition rates as high as 240 MHz and burst repetition rate of 1 MHz. The design process is aided by gaining knowledge regarding the nonlinear amplification process and the gain medium’s response time through mathematical modeling and numerical simulations. Burst-mode amplification in the gain-managed nonlinearity regime leads to new physical effects, whereby the amplification of one pulse depends on the other pulses constituting a burst.Item Open Access Long-term repetition-frequency stabilization of all-normal-dispersion Yb-doped fiber laser to the cesium standard(OSA, 2010) Ülgüdür, Coşkun; İlday, Ömer Fatih; Hamid, R.Repetition-frequency stabilization of a Yb-doped fiber laser to the Cesium standard is reported. Laser amplitude and phase noise is characterized. Performance is limited to 2x10-14 at 100000 averaging time by intrinsic stability of the Cs-standard.Item Open Access Nonlinear laser lithography for enhanced tribological properties(IEEE, 2015-05) Gnilitskyi, I.; Pavlov, Ihor; Rotundo, F.; Orazi, L.; Martini, C.; İlday, Fatih ÖmerThis 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.Item 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 ÖmerSummary 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.Item Open Access Response of porcine articular cartilage to irradiation by an ultrafast, burst-mode laser(Optical Society of America (OSA), 2019) Dzelzainis, T.; Hammouti, S.; Prickaerts, M.; Cassidy, K.; İlday, F. Ömer; Kalaycıoğlu, Hamit; Yavaş, S.; Karamuk, Ş.; Golaraei, A.; Barzda, V.; Akens, M.; Lilge, L.; Marjoribanks, R.Plasma-mediated ablation by ultrafast pulses is generally considered to be a material-independent process. We show that, in certain circumstances, this assumption may be invalid. Physical processes involved and the impact on applications are discussed.Item Open Access Ultra-low timing-jitter passively mode-locked fiber lasers for long-distance timing synchronization(SPIE, 2006) İlday, F. Ömer; Winter, A.; Kim J.-W.; Chen, J.; Schmüser, P.; Schlarb, H.; Kärtner, F. X.One of the key challenges for the next-generation light sources such as X-FELs is to implement a timing stabilization and distribution system to enable ∼ 10 fs synchronization of the different RF and laser sources distributed in such facilities with distances up to a few kilometers. These requirements appear to be beyond the capability of traditional RF distribution systems based on temperature-stabilized coaxial cables. A promising alternative is to use an optical transmission system: A train of pulses generated from a laser with low timing jitter is distributed over length-stabilized fiber links to remote locations. The repetition frequency of the pulse train and its higher harmonics contain the synchronization information. At the remote locations, RF signals are extracted simply by using a photodiode and a suitable bandpass filter to pick the desired harmonic of the laser repetition rate. Passively mode-locked Er-doped fiber lasers provide excellent long-term stability. The laser must have extremely low timing jitter, particularly at high frequencies (>1 kHz). Ultimately, the timing jitter is limited by quantum fluctuations in the number of photons making up the pulse and the incoherent photons added in the cavity due to spontaneous emission. The amplitude and phase noise of a home-built laser, generating 100-fs, 1-nJ pulses, was characterized. The measured phase noise (timing jitter) is sub-10 fs. from 1 kHz to Nyquist frequency. In addition to synchronization of accelerators, the ultra-low timing jitter pulse source can find applications in next-generation telecommunication systems.