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Kumar S.,Pohang University of Science and Technology | Kumar S.,Pohang Accelerator Laboratory | Kang H.-S.,Pohang Accelerator Laboratory | Kim D.-E.,Pohang University of Science and Technology | Kim D.-E.,Max Planck Center for Attosecond Science
Laser and Particle Beams | Year: 2012

For a real, meaningful pump-probe experiment with attosecond temporal resolution, an intense isolated attosecond pulse is in demand. For that purpose we report the generation of an intense isolated attosecond pulse, especially in X-ray region using a current-enhanced self-amplified spontaneous emission in a free electron laser (FEL). We use a few cycle laser pulse to manipulate the electron-bunch inside a two-period planar wiggler. In our study, we employ the electron beam parameters of Pohang Accelerator Laboratory (PAL)-XFEL. The RF phase effect of accelerator columns on the longitudinal energy distribution profile and current profile of electron-bunch is also studied, aiming that these results can be experimentally realized in PAL-XFEL. We show indeed that the manipulation of electron-energy bunch profile may lead to the generation of an isolated attosecond hard X-ray pulse: 150 attosecond radiation pulse at 0.1 nm wavelength can be generated. Copyright © 2012 Cambridge University Press.

Fattahi H.,Max Planck Institute of Quantum Optics | Fattahi H.,Ludwig Maximilians University of Munich | Schwarz A.,Max Planck Institute of Quantum Optics | Schwarz A.,Ludwig Maximilians University of Munich | And 9 more authors.
Optics Express | Year: 2014

The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime. © 2014 Optical Society of America.

An J.,Samsung | Pyun K.,Samsung | Kwon O.,Pohang University of Science and Technology | Kwon O.,Max Planck Center for Attosecond Science | And 2 more authors.
Optics Express | Year: 2013

An autocorrelator based on a Fabry-Perot interferometer is proposed for ultrashort pulse measurement. Main features of this autocorrelator due to the superposition of multiple pulses were investigated experimentally and theoretically. It turns out that the signal from a Fabry-Perot interferometer can be used as an autocorrelator signal. This autocorrelator provides more compact setup with a much easier alignment than a conventional autocorrelator based on a Michelson interferometer. © 2013 Optical Society of America.

Prinz S.,TRUMPF Scientific Lasers GmbH Co. KG | Prinz S.,TU Munich | Haefner M.,TRUMPF Scientific Lasers GmbH Co. KG | Teisset C.Y.,TRUMPF Scientific Lasers GmbH Co. KG | And 13 more authors.
Optics Express | Year: 2015

We report on a CEP-stable OPCPA system reaching multi-GW peak powers at 300 kHz repetition rate. It delivers 15 W of average power, over 50 μJ of compressed pulse energy and a pulse duration below 6 fs. By implementing an additional pump-seed-synchronization, the output parameters are stabilized over hours with power fluctuations of less than 1.5%. © 2015 Optical Society of America.

PubMed | Daegu Gyeongbuk Institute of Science and Technology, Pohang Accelerator Laboratory, Paul Scherrer Institute, RIKEN and Max Planck Center for Attosecond Science
Type: Journal Article | Journal: Journal of synchrotron radiation | Year: 2016

A method is proposed to generate an isolated attosecond X-ray pulse in free-electron lasers, using irregularly spaced current peaks induced in an electron beam through interaction with an intense short-pulse optical laser. In comparison with a similar scheme proposed in a previous paper, the irregular arrangement of current peaks significantly improves the contrast between the main and satellite pulses, enhances the attainable peak power and simplifies the accelerator layout. Three different methods are proposed for this purpose and achievable performances are computed under realistic conditions. Numerical simulations carried out with the best configuration show that an isolated 7.7keV X-ray pulse with a peak power of 1.7TW and pulse length of 70as can be generated. In this particular example, the contrast is improved by two orders of magnitude and the peak power is enhanced by a factor of three, when compared with the previous scheme.

Park I.-Y.,Korea Advanced Institute of Science and Technology | Park I.-Y.,Korea Research Institute of Standards and Science | Choi J.,Korea Advanced Institute of Science and Technology | Lee D.-H.,Korea Advanced Institute of Science and Technology | And 3 more authors.
Annalen der Physik | Year: 2013

Recent experimental data of high-order harmonic generation (HHG), obtained by use of the plasmonic field enhancement of nanostructure bowties and funnel-waveguides, are presented. Emphasis is laid on reproduction of previous experimental results and also elucidation of the fundamental limitations associated with the nanostructure thermal damage, small laser-gas interaction volume, and atomic line emission in the plasmon-driven HHG process. In addition, the dominance of coherent harmonics is quantitatively verified by implementing a two-beam interference experiment using a pair of funnel-waveguides. This study proves that funnel-waveguides are a superior plasmonic device capable of providing not only high thermal immunity but also sufficient atom emitters to produce practically usable extreme-ultraviolet (EUV) radiation in a reproducible manner. © 2012 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Paranthaman S.,Pusan National University | Paranthaman S.,Max Planck Center for Attosecond Science | Hong K.,Pusan National University | Kim J.,Catholic University of Korea | And 3 more authors.
Journal of Physical Chemistry A | Year: 2013

We report the results of a benchmarking study on hybrid, hybrid-meta, long-range-corrected, meta-generalized gradient approximation (meta-GGA), and GGA density functional theory (DFT) methods for aluminum (Al) clusters. A range of DFT functionals, such as B3LYP, B1B95, PBE0, mPW1PW91, M06, M06-2X, ωB97X, ωB97XD, TPSSh, BLYP, PBE, mPWPW91, M06-L, and TPSS, have been used to optimize the molecular structures and calculate the vibrational frequencies and four energetic parameters for neutral and anionic Aln (n = 2-10) clusters. The performances of these functionals are assessed systematically by calculating the vertical ionization energy for neutral Al clusters and the vertical electron detachment energy for anionic Al clusters, along with the cohesive energy and dissociation energy. The results are compared with the available experimental and high-level ab initio calculated results. The calculated results showed that the PBE0 and mPW1PW91 functionals generally provide better results than the other functionals studied. TPSS can be a good choice for the calculations of very large Al clusters. On the other hand, the B3LYP, BLYP, and M06-L functionals are in poor agreement with the available experimental and theoretical results. The calculated results suggest that the hybrid DFT functionals like B3LYP do not always provide better performance than GGA functionals. © 2013 American Chemical Society.

Choi J.,Korea Advanced Institute of Science and Technology | Kim S.,Korea Advanced Institute of Science and Technology | Kim S.,Max Planck Center for Attosecond Science | Park I.-Y.,Korea Advanced Institute of Science and Technology | And 4 more authors.
New Journal of Physics | Year: 2012

We theoretically investigated the possibility of generating attosecond pulses by means of plasmonic field enhancement induced in a nano-structured metallic funnel-waveguide. This study was motivated by our recent experimental demonstration of ultrashort extreme-ultraviolet (EUV) pulses using the same type of three-dimensional waveguides. Here, with emphasis on generation of isolated attosecond pulses, the finite-domain time-difference method was used to analyze the funnel-waveguide with respect to the geometry-dependent plasmonic features such as the field enhancement factor, enhanced plasmonic field profile and hot-spot location. Then an extended semi-classical model of high-order harmonic generation was adopted to predict the EUV spectra generated from the funnel-waveguide in consideration of the spatial inhomogeneity of the plasmonic field within the hot-spot volume. Our simulation finally proved that isolated attosecond pulses can be produced at fast repetition rates directly from a few-cycle femtosecond laser or by synthesizing a two-color laser consisting of two multi-cycle pulses of cross-polarized configuration. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Kumar S.,Daegu Gyeongbuk Institute of Science and Technology | Kang H.-S.,Pohang Accelerator Laboratory | Kim D.E.,Daegu Gyeongbuk Institute of Science and Technology | Kim D.E.,Max Planck Center for Attosecond Science
Optics Express | Year: 2015

We demonstrate that the amplification of attosecond pulse in X-ray free electron laser (FEL) undulator can be tailored. The characteristic of the amplification of an isolated attosecond pulse in the FEL undulator is investigated. An isolated 180 attoseconds full width half maximum (FWHM) pulse at 1.25 nm with a spectral bandwidth of 1% is injected into an undulator. The simulation results show that for a direct seeding of 3MW, the seed is amplified to the peak power of 106 GW (40 μJ, an output pulsewidth of 383 attoseconds) in the presence of a detuning at FEL resonance condition in 100-m long undulator. We note that the introduction of detuning leads to the better performance compared to the case without detuning: shorter by 15.5% in a pulse-width and higher by 76.6% in an output power. Tapering yields a higher power (116% increases in the output power compared to the case without detuning) but a longer pulse (15.4% longer in the pulse-width). It was observed that ± Δλr8 (Delta;λr/λr ∼1%) is the maximum degree of detuning, beyond which the amplification becomes poor: lower in the output power and longer in the pulse duration. The minimum power for a seed pulse needs to be higher than 1 MW for the successful amplification of an attosecond pulse at 1.25 nm. Also, the electron beam energy-spread must be less than 0.1% for a suitable propagation of attosecond pulse along the FEL undulator under this study. © 2015 Optical Society of America.

PubMed | Max Planck Center for Attosecond Science, Catholic University of Korea and Pusan National University
Type: Journal Article | Journal: The journal of physical chemistry. A | Year: 2016

Herein a performance assessment of density functionals used for calculating the structural and energetic parameters of bi- and trimetallic Ru-containing organometallic complexes has been performed. The performance of four popular relativistic effective core potentials (RECPs) has also been assessed. On the basis of the calculated results, the MN12-SX (range-separated hybrid functional) demonstrates good performance for calculating the molecular structures, while MN12-L (local functional) performs well for calculating the energetics, including that of the Ru-Ru bond breaking process. The choice of appropriate density functional is a crucial factor for calculating the energetics. The LANL08 demonstrates the lowest performance of the RECPs for calculating the molecular structures, especially the Ru-Ru bond length.

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