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- 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.
- ItemStability of quantum linear logic circuits against perturbations(Bristol : IOP Publ., 2020) Babushkin, Ihar; Morgner, Uwe; Demircan, AyhanHere we study transformation of waveshapes of photons under the action of the linear logic circuits and other related architectures involving only linear optical networks and measurements. We show that the gates are working well not only in the case when all photons are separable and located in the same mode, but in some more general cases. For instance, the photonic waveshapes are allowed to be slightly different in different channels; in this case, Zeno effect prevents the photons from decoherence after the measurement, and the gate thus remains neutral to the small waveshape perturbations. © 2020 The Author(s). Published by IOP Publishing Ltd Printed in the UK
- 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.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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]
- ItemSymmetry breaking and strong persistent plasma currents via resonant destabilization of atoms(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2017) Brée, Carsten; Hofmann, Michael; Babushkin, Ihar; Demircan, Ayhan; Morgner, Uwe; Kosareva, Olga G.; Savelev, Andrei B.; Husakou, Anton; Ivanov, MishaThe ionization rate of an atom in a strong optical field can be resonantly enhanced by the presence of long-living atomic levels (so called Freeman resonances). This process is most prominent in the multiphoton ionization regime meaning that ionization event takes many optical cycles. Nevertheless, here we show that these resonances can lead to fast subcycle-scale plasma buildup at the resonant values of the intensity in the pump pulse. The fast buildup can break the cycletocycle symmetry of the ionization process, resulting in generation of persistent macroscopic plasma currents which remain after the end of the pulse. This, in turn, gives rise to a broadband radiation of unusual spectral structure forming a comb from terahertz (THz) to visible. This radiation contains fingerprints of the attosecond electronic dynamics in Rydberg states during ionization.