Browsing by Author "Demircan, Ayhan"
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- ItemAccelerated rogue solitons triggered by background radiation(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2015) Demircan, Ayhan; Amiranashvili, Shalva; Brée, Carsten; Morgner, Uwe; Steinmeyer, Günter[no abstract available]
- ItemAdjustable pulse compression scheme for generation of few-cycle pulses in the mid-infrared(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Demircan, Ayhan; Amiranashvili, Shalva; Brée, Carsten; Morgner, Uwe; Steinmeyer, GünterAn novel adjustable adiabatic soliton compression scheme is presented, enabling a coherent pulse source with pedestal-free few-cycle pulses in the infrared or mid-infrared regime. This scheme relies on interaction of a dispersive wave and a soliton copropagating at nearly identical group velocities in a fiber with enhanced infrared transmission. The compression is achieved directly in one stage, without necessity of an external compensation scheme. Numerical simulations are employed to demonstrate this scheme for silica and fluoride fibers, indicating ultimate limitations as well as the possibility of compression down to the single-cycle regime. Such output pulses appear ideally suited as seed sources for parametric amplification schemes in the mid-infrared.
- ItemAll-optical supercontinuum switching(London : Springer Nature, 2020) Melchert, Oliver; Brée, Carsten; Tajalli, Ayhan; Pape, Alexander; Arkhipov, Rostislav; Willms, Stephanie; Babushkin, Ihar; Skryabin, Dmitry; Steinmeyer, Günter; Morgner, Uwe; Demircan, AyhanEfficient all-optical switching is a challenging task as photons are bosons and cannot immediately interact with each other. Consequently, one has to resort to nonlinear optical interactions, with the Kerr gate being the classical example. However, the latter requires strong pulses to switch weaker ones. Numerous approaches have been investigated to overcome the resulting lack of fan-out capability of all-optical switches, most of which relied on types of resonant enhancement of light-matter interaction. Here we experimentally demonstrate a novel approach that utilizes switching between different portions of soliton fission induced supercontinua, exploiting an optical event horizon. This concept enables a high switching efficiency and contrast in a dissipation free setting. Our approach enables fan-out, does not require critical biasing, and is at least partially cascadable. Controlling complex soliton dynamics paves the way towards building all-optical logic gates with advanced functionalities. © 2020, The Author(s).
- ItemAnalysis of the interplay between soliton fission and modulation instability in supercontinuum generation(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Demircan, Ayhan; Bandelow, UweWe investigate the generation mechanisms for ultrawide spectra in nonlinear optical fibers. Soliton fission and modulation instability represent fundamental mechanisms for the generation process. The primary origin of the spectral broadening changes with the pump-pulse duration. Soliton fission dominates for low input power and short pulses. Its efficiency for supercontinuum generation and especially the extend to the blue side can be increased by proper design of the dispersion profile. The modulation instability has a strong impact for high input powers and greatly enhances the generation process, but leads to a degradation of the coherence properties. Also for short pulses with durations of 60 fs the modulation instability is present and can hardly be suppressed. The interplay between these two effects leads to various characteristics of the resulting spectra, which are modified by to the relative impact of the modulation instability.
- ItemAsymptotic pulse shapes in filamentary propagation of intense femtosecond pulses(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2008) Krüger, Carsten; Demircan, Ayhan; Steinmeyer, GünterSelf-compression of intense ultrashort laser pulses inside a self-guided filament is discussed. The filament self-guiding mechanism requires a balance between diffraction, plasma self-defocusing and Kerr-type self-focusing, which gives rise to asymptotic intensity profiles on axis of the filament. The asymptotic solutions appear as the dominant pulse shaping mechanism in the leading part of the pulse, causing a pinch of the photon density close to zero delay, which substantiates as pulse compression. The simple analytical model is backed up by numerical simulations, confirming the prevalence of spatial coupling mechanisms and explaining the emerging inhomogeneous spatial structure. Numerical simulations confirm that only spatial effects alone may already give rise to filament formation. Consequently, self-compression is explained by a dynamic balance between two optical nonlinearities, giving rise to soliton-like pulse formation inside the filament.
- ItemCascaded self-compression of femtosecond pulses in filaments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Brée, Carsten; Bethge, Jens; Skupin, Stefan; Demircan, Ayhan; Steinmeyer, GünterHighly nonlinear wave propagation scenarios hold the potential to serve for energy concentration or pulse duration reduction of the input wave form, provided that a small range of input parameters be maintained. In particular when phenomena like rogue-wave formation or few-cycle optical pulses generation come into play, it becomes increasingly difficult to maintain control of the waveforms. Here we suggest an alternative approach towards the control of waveforms in a highly nonlinear system. Cascading pulse self-compression cycles at reduced nonlinearity limits the increase of input parameter sensitivity while still enabling an enhanced compression effect. This cascaded method is illustrated by experiments and in numerical simulations of the Nonlinear Schrödinger Equation, simulating the propagation of short optical pulses in a self-generated plasma.
- ItemCompression limit by third-order dispersion in the normal dispersion regime(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Demircan, Ayhan; Kroh, Marcel; Bandelow, Uwe; Hüttl, Bernd; Weber, Hans-GeorgBroad-band continua at gigahertz rates generated in high-nonlinear dispersion flattened fibers in the normal dispersion regime near the zero-dispersion wavelength can be used for a subsequent efficient pulse compression, leading to stable high-repetition-rate trains of femtosecond pulses. We show experimentally and theoretically that third-order dispersion defines a critical power, where beyond further compression is inhibited. This fundamental limit is caused by a pulse-breakup.
- ItemThe Effect of Chirp on Pulse Compression at a Group Velocity Horizon(New York, NY : IEEE, 2016) Babushkin, Ihar; Amiranashvili, Shalva; Bree, Carsten; Morgner, Uwe; Steinmeyer, Gunter; Demircan, AyhanGroup-velocity matched cross-phase modulation between a fundamental soliton and a dispersive wave packet has been previously suggested for optical switching applications similar to an optical transistor. Moreover, the nonlinear interaction in the resulting group-velocity horizon can be exploited for adiabatic compression of the soliton down into the few-cycle regime. Here, we study the delicate phase- and frequency-matching mechanism of soliton/dispersive wave interaction by controlling the input chirp of the dispersive wave. We demonstrate that such a modification of the dispersive wave can significantly alter the soliton dynamics. In particular, we show that it allows a decrease of the fiber length needed for the best compression and, to some extent, control of the trajectory of the soliton. The mechanism of such an influence is related to the modification of the phase-matching condition between the soliton and dispersive wave.
- ItemEffect of higher-order dispersion on modulation instability, soliton propagation and pulse splitting(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2007) Demircan, Ayhan; Pietrzyk, Monika; Bandelow, UweBy solving numerically the extended nonlinear Schrödinger equation we investigate the influence of higher-order dispersion effects on the propagation of optical pulses in highly nonlinear fibers. In the anomalous dispersion regime third-order dispersion can, in general, induce soliton fission and yields asymmetric spectra, whereas modulation instability can be slightly suppressed. In the normal dispersion regime we demonstrate pulse splitting by third-order dispersion, as well as its later suppression by fourth-order dispersion.
- ItemFemtosecond Field‐Driven On‐Chip Unidirectional Electronic Currents in Nonadiabatic Tunneling Regime(Weinheim : Wiley VCH, 2021) Shi, Liping; Babushkin, Ihar; Husakou, Anton; Melchert, Oliver; Frank, Bettina; Yi, Juemin; Wetzel, Gustav; Demircan, Ayhan; Lienau, Christoph; Giessen, Harald; Ivanov, Misha; Morgner, Uwe; Kovacev, MilutinRecently, asymmetric plasmonic nanojunctions have shown promise as on-chip electronic devices to convert femtosecond optical pulses to current bursts, with a bandwidth of multi-terahertz scale, although yet at low temperatures and pressures. Such nanoscale devices are of great interest for novel ultrafast electronics and opto-electronic applications. Here, the device is operated in air and at room temperature, revealing the mechanisms of photoemission from plasmonic nanojunctions, and the fundamental limitations on the speed of optical-to-electronic conversion. Inter-cycle interference of coherent electronic wavepackets results in a complex energy electron distribution and birth of multiphoton effects. This energy structure, as well as reshaping of the wavepackets during their propagation from one tip to the other, determine the ultrafast dynamics of the current. It is shown that, up to some level of approximation, the electron flight time is well-determined by the mean ponderomotive velocity in the driving field.
- ItemFilamentary pulse self-compression : the impact of the cell windows(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Brée, Carsten; Demircan, Ayhan; Bethge, Jens; Nibbering, Erik T.J.; Skupin, Stefan; Bergé, Luc; Steinmeyer, GünterSelf-compression of multi-millijoule laser pulses during filamentary propagation is usually explained by the interplay of self-focusing and defocusing effects, causing a substantial concentration of energy on the axis of the propagating optical pulse. Recently, it has been argued that cell windows may play a decisive role in the self-compression mechanism. As such windows have to be used for media other than air their presence is often unavoidable, yet they present a sudden non-adiabatic change in dispersion and nonlinearity that should lead to a destruction of the temporal and spatial integrity of the light bullets generated in the self-compression mechanism. We now experimentally prove that there is in fact a self-healing mechanism that helps to overcome the potentially destructive consequences of the cell windows. We show in two carefully conducted experiments that the cell window position decisively influences activation or inhibition of the self-healing mechanism. A comparison with a windowless cell shows that presence of this mechanism is an important prerequisite for the exploitation of self-compression effects in windowed cells filled with inert gases.
- ItemHamiltonian structure of propagation equations for ultrashort optical pulses(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Amiranashvili, Shalva; Demircan, AyhanA Hamiltonian framework is developed for a sequence of ultrashort optical pulses propagating in a nonlinear dispersive medium. To this end a second-order nonlinear wave equation is first simplified using an unidirectional approximation. All non-resonant nonlinear terms are then rigorously eliminated using a suitable change of variables in the spirit of the canonical perturbation theory. The derived propagation equation operates with a properly defined complexification of the real electric field. It accounts for arbitrary dispersion, four-wave mixing processes, weak absorption, and arbitrary pulse duration. Thereafter the so called normal variables, i.e., classical fields corresponding to the quantum creation and annihilation operators, are introduced. Neglecting absorption we finally derive the Hamiltonian formulation. The latter yields the most essential integrals of motion for the pulse propagation. These integrals reflect the time-averaged fluxes of energy, momentum, and classical photon number transferred by the pulse. The conservation laws are further used to control the numerical solutions when calculating supercontinuum generation by an ultrashort optical pulse.
- ItemKramers-Kronig relations and high order nonlinear susceptibilities(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Brée, Carsten; Demircan, Ayhan; Steinmeyer, GünterAs previous theoretical results recently revealed, a Kramers-Kronig transform of multiphoton absorption rates allows for a precise prediction on the dispersion of the nonlinear refractive index $n_2$ in the near IR. It was shown that this method allows to reproduce recent experimental results on the importance of the higher-order Kerr effect. Extending these results, the current manuscript provides the dispersion of $n_2$ for all noble gases in excellent agreement with reference data. It is furthermore established that the saturation and inversion of the nonlinear refractive index is highly dispersive with wavelength, which indicates the existence of different filamentation regimes. While shorter laser wavelengths favor the well-established plasma clamping regime, the influence of the higher-order Kerr effect dominates in the long wavelength regime.
- ItemLimit for pulse compression by pulse splitting(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Demircan, Ayhan; Bandelow, UweWe have detected a fundamental pulse-compression limit for high-nonlinear fibers in the normal dispersion regime near the zero-dispersion wavelength. The desired generation of a broadband continuum by self-phase modulation is limited by already small amounts of third-order dispersion, which results in pulse splitting above a critical pulse power. We investigate the critical fiber length in dependence on pulse- and fiber parameters.
- ItemMethod for computing the nonlinear refractive index via Keldysh theory(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2008) Brée, Carsten; Demircan, Ayhan; Steinmeyer, GünterBy making use of the multiphoton limit of Keldysh theory, we show that for the case of two-photon absorption a Kramers-Kronig expansion can be used to calculate the nonlinear refractive index for different wavelenghts. We apply this method to various inert gases and compare the obtained numerical values to different experimental and theoretical results for the dispersion of the Kerr nonlinearity.
- ItemModulation instability in filamentary self-compression(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Brée, Carsten; Demircan, Ayhan; Steinmeyer, GünterWe numerically analyze filamentary propagation for various medium- and input pulse parameters and show that temporal self-compression can greatly benefit from refocusing events. Analyzing the dynamical behavior in the second focal spot, it turns out that a dispersive temporal break-up may appear due to the emission of a hyperbolic shock-wave from the self-steepened trailing edge of the pulse. This break-up event enhances the self-compression capabilities of laser filaments, enabling up to 12-fold temporal compression. Only slightly perturbing the input pulse parameters, we further identify a regime in which refocusing events give rise to extended subdiffractive propagation in a weakly ionized channel.
- ItemNon-instantaneous polarization dynamics in dielectric media(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Hofmann, Michael; Hyyti, Janne; Birkholz, Simon; Bock, Martin; Das, Susanta K.; Grunwald, Rüdiger; Hoffmann, Mathias; Nagy, Tamas; Demircan, Ayhan; Jupé, Marco; Ristau, Detlev; Morgner, Uwe; Brée, Carsten; Woerner, Michael; Elsaesser, Thomas; Steinmeyer, GünterThird-order optical nonlinearities play a vital role for generation1,2 and characterization 3-5 of some of the shortest optical pulses to date, for optical switching applications6,7, and for spectroscopy8,9. In many cases, nonlinear optical effects are used far off resonance, and then an instantaneous temporal response is expected. Here, we show for the first time resonant frequency-resolved optical gating measurements1012 that indicate substantial nonlinear polarization relaxation times up to 6.5 fs in dielectric media, i.e., significantly beyond the shortest pulses directly available from commercial lasers. These effects are among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrödinger equation13,14 are in excellent agreement with experimental observations. The simulations indicate that pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect. Moreover, our approach opens an avenue for application of frequency-resolved optical gating as a highly selective spectroscopic probe in high-field physics.
- ItemNon-Raman redshift by pulse splitting in the normal dispersion regime(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2007) Demircan, Ayhan; Kroh, Marcel; Bandelow, UweWhile usually the generation of a Stokes component is attributed to Raman scattering, we present here experimentally and numerically a more fundamental mechanism which can be explained by the nonlinear Schrödinger equation alone. It can be employed to excite new frequency components on the red side, by using pulse splitting in the normal dispersion regime.
- ItemOcean rogue waves and their phase space dynamics in the limit of a linear interference model(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2016) Birkholz, Simon; Brée, Carsten; Veselic, Ivan; Demircan, Ayhan; Steinmeyer, GünterWe reanalyse the probability for formation of extreme waves using the simple model of linear interference of a finite number of elementary waves with fixed amplitude and random phase fluctuations. Under these formation becomes increasingly likely, with appearance frequencies that may even exceed long-term observations by an order of magnitude. For estimation of the effective number of interfering waves, we suggest the Grassberger-Procaccia dimensional analysis of individual time series. For the ocean system, it is further shown that the resulting phase space dimension may vary, such that the threshold for rogue wave formation is not always reached. Time series analysis as well as the appearance of particular focusing wind conditions may enable an effective forecast of such rogue-wave prone situations. In particular, extracting the dimension from ocean time series allows much more specific estimation of the rogue wave probability.
- ItemOcean rogue waves and their phase space dynamics in the limit of a linear interference model([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Birkholz, Simon; Brée, Carsten; Veselić, Ivan; Demircan, Ayhan; Steinmeyer, GünterWe reanalyse the probability for formation of extreme waves using the simple model of linear interference of a finite number of elementary waves with fixed amplitude and random phase fluctuations. Under these model assumptions no rogue waves appear when less than 10 elementary waves interfere with each other. Above this threshold rogue wave formation becomes increasingly likely, with appearance frequencies that may even exceed long-term observations by an order of magnitude. For estimation of the effective number of interfering waves, we suggest the Grassberger-Procaccia dimensional analysis of individual time series. For the ocean system, it is further shown that the resulting phase space dimension may vary, such that the threshold for rogue wave formation is not always reached. Time series analysis as well as the appearance of particular focusing wind conditions may enable an effective forecast of such rogue-wave prone situations. In particular, extracting the dimension from ocean time series allows much more specific estimation of the rogue wave probability.