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Lee D.-H.,Korea Advanced Institute of Science and Technology | Choi J.,Korea Advanced Institute of Science and Technology | Kim S.,Max Planck Center for Attosecond Science | Park I.-Y.,Korea Research Institute of Standards and Science | And 3 more authors.
Optics Express | Year: 2014

For strong field enhancement of ultrashort light pulses, a 3-D metallic funnel-waveguide is analyzed using the finite-difference timedomain (FDTD) method. Then the maximum intensity enhancement actually developed by the funnel-waveguide upon the injection of femtosecond laser pulses is observed using two-photon luminescence (TPL) microscopy. In addition, the ultrafast dephasing profile of the localized field at the hot spot of the funnel-waveguide is verified through the interferometric autocorrelation of the TPL signal. Finally it is concluded the funnel-waveguide is an effective 3-D nanostructure that is capable of boosting the peak pulse intensity of stronger than 80 TWcm-2 by an enhancement factor of 20 dB without significant degradation of the ultrafast spatiotemporal characteristics of the original pulses. © 2014 Optical Society of America.

Chen G.,Shanghai University of Engineering Science | Geng X.,Pohang University of Science and Technology | Xu H.,Shanghai University of Engineering Science | Mi Y.,Shanghai University of Engineering Science | And 4 more authors.
AIP Advances | Year: 2013

This work aims to understand the cluster size deviation from the prediction by an existing scaling law for conical nozzles. The dimensions of cluster jet at different heights above a nozzle along the direction of gas flow are measured. This study indicates that the dimension of cluster jet is underestimated in the existing scaling law and this under-estimation leads to the over-estimation of the equivalent diameter of conical nozzle. Thus the underestimation of the dimension of cluster jet may be one of possible factors responsible for the cluster size deviation (the degree of the deviation depends on details of cluster jet). © 2013 Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.

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.

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.

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