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Toth A.,ELI HU Non Profit Ltd | Borbely S.,Babes - Bolyai University | Halasz G.J.,Debrecen University | Vibok A.,ELI HU Non Profit Ltd | Vibok A.,Debrecen University
Chemical Physics Letters | Year: 2017

Theoretical ab initio investigation of strong field dissociative ionization of the D2+ molecule in the multiphoton regime is reported. The dynamics is initiated by ultrashort laser pulses for fixed molecular axis orientations. Nuclear wave packet calculations are performed to provide the joint energy spectra (JES): ionization-dissociation probability density via electron (Ee) and nuclear (En) kinetic energy. Analyzing the time-dependent nuclear wave packet densities we have successfully identified the exact path followed by the D2+ target for each multiphoton peak. © 2017 Elsevier B.V.

Lecz Z.,ELI HU Nonprofit Ltd. | Andreev A.,ELI HU Nonprofit Ltd. | Andreev A.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy
Physics of Plasmas | Year: 2017

This paper proposes an intense x-ray source based on the interactions of intense laser pulses with nanowire targets. The presented electron dynamics and energy scalings have been studied by three dimensional particle-in-cell simulations. The resonance of the electronic betatron oscillations with the incident laser field results in extremely high energy electrons. The scaling of radiation intensity is predicted to be ∼ I L 5 / 2, where IL is the laser intensity, using optimal parameters. In this case, the number of photons emitted, via synchrotron radiation, with energies above the keV level with 0.1 rad angular spread is greater than 10 8 /fs for intensities I L > 10 20 W/cm2. This scaling law suggests that the photon flux production using nanowires of suitable lengths is much greater than in a underdense plasma. © 2017 Author(s).

Nagymihaly R.S.,ELI HU Non Profit Ltd. | Nagymihaly R.S.,University of Szeged | Jojart P.,ELI HU Non Profit Ltd. | Jojart P.,University of Szeged | And 3 more authors.
Optics Express | Year: 2017

The spectral phase noise of a cryogenically cooled Ti:Sapphire amplifier was analyzed by spectrally resolved interferometry. Since a relative phase difference measurement is performed, the effect of the amplifier stage can be determined with high precision. Contributions of the cooling system to the spectral phase noise were found to be below 50 mrad for both the vacuum pumps and the cryogenic system. The carrier-envelope phase noise of thermal and mechanical origin was also determined for different repetition rates of laser operation. Mechanical vibrational spectra were recorded by an accelerometer for different stages of operation and compared to the interferometric phase noise measurements. © 2017 Optical Society of America.

Polonyi G.,MTA PTE High Field Terahertz Research Group | Mechler M.I.,MTA PTE High Field Terahertz Research Group | Hebling J.,MTA PTE High Field Terahertz Research Group | Hebling J.,University of Pécs | And 2 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2017

Extremely high pump-to-terahertz (THz) conversion efficiencies up to 0.7% were demonstrated in recent experiments with ZnTe THz pulse sources. Such high efficiencies could be achieved by pumping at an infrared wavelength sufficiently long to suppress both two- and three-photon absorption and the associated free-carrier absorption at THz frequencies. Here, high-field high-energy THz pulse generation by optical rectification in semiconductor nonlinear materials is investigated by numerical simulations. Basic design aspects of infrared-pumped semiconductor THz sources are discussed. Optimal pumping and phase-matching conditions are given. Multicycle THz pulse generation for particle acceleration is discussed. © 2017 IEEE.

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.

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.

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.

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