7 results
Search Results
Now showing 1 - 7 of 7
- ItemHamiltonian framework for short optical pulses(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Amiranashvili, ShalvaPhysics of short optical pulses is an important and active research area in nonlinear optics. In what follows we theoretically consider the most extreme representatives of short pulses that contain only several oscillations of electromagnetic field. Description of such pulses is traditionally based on envelope equations and slowly varying envelope approximation, despite the fact that the envelope is not ?slow? and, moreover, there is no clear definition of such a ?fast? envelope. This happens due to another paradoxical feature: the standard (envelope) generalized nonlinear Schrödinger equation yields very good correspondence to numerical solutions of full Maxwell equations even for few-cycle pulses, a thing that should not be. In what follows we address ultrashort optical pulses using Hamiltonian framework for nonlinear waves. As it appears, the standard optical envelope equation is just a reformulation of general Hamiltonian equations. In a sense, no approximations are required, this is why the generalized nonlinear Schrödinger equation is so effective. Moreover, the Hamiltonian framework greatly contributes to our understanding of ?fast? envelope, ultrashort solitons, stability and radiation of optical pulses. Even the inclusion of dissipative terms is possible making the Hamiltonian approach an universal theoretical tool also in extreme nonlinear optics.
- ItemVerbundprojekt: Grundlegende Untersuchungen zu neuen Konzepten für Ultrakurzpuls-Laser, Teilvorhaben: Abstimmbare diodengepumpte Ultrakurzpulslaser im NIR (1.1-1.6[my]): Modensynchronisation von Cr4+-dotierten Festkörpermaterialien : Abschlußbericht(Berlin : Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 2001) Noack, Frank; Jäger, Frank[no abstract available]
- ItemFemtosecond filamentation by intensity clamping at a Freeman resonance(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Hofmann, Michael; Brée, Carsten[no abstract available]
- ItemTailoring THz radiation by controlling tunnel photoionization events in gases(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Babushkin, Ihar; Skupin, Stefan; Husakou, Anton; Köhler, Christian; Cabrera-Granado, Eduardo; Bergé, Luc; Herrmann, JoachimjApplications ranging from nonlinear terahertz spectroscopy to remote sensing require broadband and intense THz radiation which can be generated by focusing two-color laser pulses into a gas. In this setup, THz radiation originates from the buildup of the electron density in sharp steps of attosecond duration due to tunnel ionization, and subsequent acceleration of free electrons in the laser field. We show that the spectral shape of the THz pulses generated by this mechanism is determined by superposition of contributions from individual ionization events. This provides a straightforward analogy with linear diffraction theory, where the ionization events play the role of slits in a grating. This analogy offers simple explanations for recent experimental observations and opens new avenues for THz pulse shaping based on temporal control of the ionization events. We illustrate this novel technique by tailoring the spectral width and position of the resulting radiation using multi-color pump pulses.
- ItemDirectionality of THz emission from photoinduced gas plasmas(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Köhler, Christian; Cabrera-Granado, Eduardo; Babushkin, Ihar; Bergé, Luc; Herrmann, Joachim; Skupin, StefanForward and backward THz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semi-analytical model based on Jefimenko's equation and rigorous Maxwell simulations in one and two dimensions. We find the emission in backward direction having a much smaller spectral bandwidth than in forward direction and explain this by interference effects. Forward THz radiation is generated predominantly at the ionization front and is thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model.
- ItemImpact of spatial inhomogeneities on on-axis pulse reconstruction in femtosecond filaments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Brée, Carsten; Kretschmar, Martin; Nagy, Tamas; Kurz, Heiko G.; Morgner, Uwe; Kovačev, MilutinWe demonstrate a strong influence of the spatial beam profile on the vacuum-propagated on-axis pulse shapes for a femtosecond filament in argon. The effects can be minimized by transmitting the filament into the far-field by a laser-drilled pinhole setup. Using this method, we can monitor the pulse compression dynamics along the entire longitudinal extension of the filament, including the ionization-induced plasma channel.
- ItemAdditive splitting methods for parallel solution of evolution problems(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2020) Amiranashvili, Shalva; Radziunas, Mindaugas; Bandelow, Uwe; Busch, Kurt; Čiegis, RaimondasWe demonstrate how a multiplicative splitting method of order P can be used to construct an additive splitting method of order P + 3. The weight coefficients of the additive method depend only on P, which must be an odd number. Specifically we discuss a fourth-order additive method, which is yielded by the Lie-Trotter splitting. We provide error estimates, stability analysis, and numerical examples with the special discussion of the parallelization properties and applications to nonlinear optics.