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Jacqmin H.,Polytechnic School of Algiers | Jacqmin H.,Thales Alenia | Jullien A.,Polytechnic School of Algiers | Mercier B.,Polytechnic School of Algiers | And 2 more authors.
Journal of the Optical Society of America B: Optical Physics | Year: 2015

We propose a detailed analysis of a temporal multiplexing technique suited to the post-compression of energetic femtosecond laser pulses in gas-filled hollow-core fibers down to the few-cycle regime. Twofold temporal division and combination are achieved using two birefringent plates with specific crystallographic orientation. We demonstrate a simple interferometric method for measuring the relative spectral phase between two replicas, which gives a measure of the phase mismatch in the combining plate, as well as that induced by eventual cross-phase modulation or ionization during propagation in the fiber. We present the experimental conditions required for producing few-cycle pulses with high fidelity. This passive combination technique will aid the energy scaling of hollow fiber compressors to the multi-millijoule level. © 2015 Optical Society of America.

Jacqmin H.,Polytechnic School of Algiers | Jacqmin H.,Thales Alenia | Mercier B.,Polytechnic School of Algiers | Jullien A.,Polytechnic School of Algiers | And 2 more authors.
Applied Physics B: Lasers and Optics | Year: 2016

We demonstrate fourfold coherent combining in a gas-filled hollow-fiber compressor with 92 % efficiency. Our passive approach relies on the use of carefully oriented birefringent plates for temporal pulse dividing and combining. We perform a detailed theoretical and experimental analysis of the effects degrading the combining process, as polarization change or nonlinear interactions between pulse replicas. We show how to overcome these limitations to generate 10-fs output pulses with high temporal quality. © 2016, Springer-Verlag Berlin Heidelberg.

Cserteg A.,Furukawa Electric Institute of Technology Ltd. | Sagi V.,Budapest University of Technology and Economics | Drozdy A.,ELI HU Non Profit Ltd. | Varallyay Z.,Furukawa Electric Institute of Technology Ltd. | Gajdatsy G.,Furukawa Electric Institute of Technology Ltd.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

An ytterbium based all-fiber, all normal dispersion fiber oscillator with integrated SESAM can have several operation modes like mode-locked, Q-switched and noise-like. To know and to control the quality of the mode-locking is essential for the application of such laser oscillators, otherwise the whole laser setup can be damaged or the expected operation characteristics of the oscillator driven systems cannot be achieved. Usually the two-photon signal generated by the short pulses is used to indicate the mode-locked operation, however such detection can be misleading in certain cases and not always able to predict the forthcoming degradation or vanishing of mode-locking. The characterization method that we propose uses only the radio frequency spectrum of the oscillator output and can identify the different operation regimes of our laser setup. The optical spectra measured simultaneously with the RF signals proves the reliability of our method. With this kind of characterization stable mode-locking can be initiated and maintained during the laser operation. The method combined with the ability to align the polarization states automatically in the laser cavity leads to the possibility to record a polarization map where the stability domains can be identified and classified. With such map the region where the mode-locking is self starting and maintainable with minimal polarization alignment can be selected. The developed oscillator reported here with its compact setup and self alignment ability can be a reliable source with long term error free operation without the need of expensive monitoring tools. © 2015 SPIE.

Varallyay Z.,FETI Ltd. | Varallyay Z.,ELI HU Nonprofit Ltd. | Kovacs P.,Budapest University of Technology and Economics
Optical Fiber Technology | Year: 2016

All-silica, photonic crystal fibres consisting of a low index, silica core surrounded by higher index inclusions embedded in a silica matrix to form a photonic bandgap cladding were numerically analysed. The aim of the investigations was to modify the guiding properties of the fibre by introducing resonant structural entities. These structural modifications are realised by altering the refractive index of certain high index inclusions in the photonic crystal cladding resulting in mode coupling between the core mode and the mode propagated in the modified index region. This results in an increased effective core area of the fundamental core mode and consequently decreased nonlinearity as well as modified effective index compared to the effective index of the unmodified structure and resonant dispersion profile that can be used for pulse compression or optical delay purposes. © 2016 Elsevier Inc. All rights reserved.

Szaszko-Bogar V.,University of Szeged | Szaszko-Bogar V.,University of Antwerp | Peeters F.M.,University of Antwerp | Foldi P.,University of Szeged | Foldi P.,ELI HU Non Profit Ltd.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We consider ballistic transport through a lateral, two-dimensional superlattice with experimentally realizable, sinusoidally oscillating, Rashba-type spin-orbit interaction (SOI). The periodic structure of the rectangular lattice produces a spin-dependent miniband structure for static SOI. Using Floquet theory, transmission peaks are shown to appear in the mini-bandgaps as a consequence of the additional, time-dependent SOI. A detailed analysis shows that this effect is due to the generation of harmonics of the driving frequency, via which, e.g., resonances that cannot be excited in the case of static SOI become available. Additionally, the transmitted current shows space- and time-dependent partial spin polarization, in other words, polarization waves propagate through the superlattice. © 2015 American Physical Society.

Majorosi S.,University of Szeged | Czirjak A.,University of Szeged | Czirjak A.,ELI HU Non Profit Ltd.
Computer Physics Communications | Year: 2016

We present a novel numerical method and algorithm for the solution of the 3D axially symmetric time-dependent Schrödinger equation in cylindrical coordinates, involving singular Coulomb potential terms besides a smooth time-dependent potential. We use fourth order finite difference real space discretization, with special formulae for the arising Neumann and Robin boundary conditions along the symmetry axis. Our propagation algorithm is based on merging the method of the split-operator approximation of the exponential operator with the implicit equations of second order cylindrical 2D Crank–Nicolson scheme. We call this method hybrid splitting scheme because it inherits both the speed of the split step finite difference schemes and the robustness of the full Crank–Nicolson scheme. Based on a thorough error analysis, we verified both the fourth order accuracy of the spatial discretization in the optimal spatial step size range, and the fourth order scaling with the time step in the case of proper high order expressions of the split-operator. We demonstrate the performance and high accuracy of our hybrid splitting scheme by simulating optical tunneling from a hydrogen atom due to a few-cycle laser pulse with linear polarization. © 2016 Elsevier B.V.

Nagymihaly R.S.,ELI HU Non Profit Ltd | Chvykov V.,ELI HU Non Profit Ltd
Advanced Solid State Lasers, ASSL 2015 | Year: 2015

Thermal simulations on petawatt scale Ti:Sapphire amplifiers were performed to investigate the thermal limits of thin disk amplification by using finite element method. Several amplifier parameters were investigated, including crystal, cooling, and pump beam properties. © OSA 2015.

Pocsai M.A.,Hungarian Academy of Sciences | Varro S.,Hungarian Academy of Sciences | Varro S.,ELI HU Nonprofit Ltd. | Barna I.F.,Hungarian Academy of Sciences | Barna I.F.,ELI HU Nonprofit Ltd.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2016

A theoretical study of laser and plasma based electron acceleration is presented. An effective model has been used, in which the presence of an underdense plasma has been taken account via its index of refraction nm. In the confines of this model, the basic phenomena can be studied by numerically solving the classical relativistic equations of motion. The key idea of this paper is the application of chirped, bichromatic laser fields. We investigated the advantages and disadvantages of mixing the second harmonic to the original λ=800nm wavelength pulse. We performed calculations both for plane wave and Gaussian pulses. © 2015 Elsevier B.V. All rights reserved.

Borzsonyi A.,University of Szeged | Borzsonyi A.,ELI HU Non Profit Ltd. | Nagymihaly R.S.,University of Szeged | Nagymihaly R.S.,ELI HU Non Profit Ltd. | Osvay K.,ELI HU Non Profit Ltd.
Laser Physics Letters | Year: 2016

We report on the drift and noise measurement of the carrier-envelope phase (CEP) of ultrashort pulses in a three-pass Ti:sapphire-based amplifier. Spectrally and spatially resolved interferometry makes it possible to investigate the absolute CEP changes due exclusively to the amplifier, that is, entirely separated from the incidental phase fluctuations of the oscillator. We found that propagation through the amplifier crystal could result in an increase up to 30 mrad noise depending on the repetition rate, cooling, and pumping conditions. Most of this noise is related to mechanical vibrations and thermal instabilities. The absolute CEP drift of thermal origin can be as large as 11 mrad/°C for each mm of the amplifier crystal, originating from inefficient heat conduction during the absorption of pump pulses. The noise of the thermal CEP drift is inversely proportional to the repetition rate, as was shown experimentally and proven by simulations. © 2016 Astro Ltd.

Halasz G.J.,Debrecen University | Csehi A.,Debrecen University | Vibok A.,Debrecen University | Vibok A.,ELI HU Non Profit Ltd
Theoretical Chemistry Accounts | Year: 2015

Nonadiabatic effects are ubiquitous in physics and chemistry. They are associated with conical intersections (CIs) which are degeneracies between electronic states of polyatomic molecules. Recently, it has been recognized that so-called light-induced conical intersections (LICIs) can be formed both by standing or by running laser waves even in diatomics. Owing to the strong nonadiabatic couplings, the appearance of such laser-induced conical intersections (LICIs) may significantly change the dynamical properties of a molecular system. In the present paper we investigate the photodissociation dynamics of $$\hbox {D}_{2}^{+}$$D2+ ion initiating the nuclear dynamics from the superposition of all the vibrational states produced by ionizing $$\hbox {D}_{2}$$D2. The kinetic energy release and the angular distribution of the photodissociation products are computed with and without LICI for the several different values of the laser parameters. We performed both one- and two-dimensional calculations, as well. In the first scheme the molecules were rotationally frozen, whereas in the latter one, the molecular rotation is included as a full additional dynamic variable. The results obtained undoubtedly demonstrate that the impact of the LICI on the dissociation dynamics of the $$\hbox {D}_{2}^{+}$$D2+ molecule strongly depend upon the laser parameters applied. © 2015, Springer-Verlag Berlin Heidelberg.

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