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PNAS - Generation of isolated attosecond bright soft X-ray pulses driven by Multicycle midinfrared lasers. (M.C. Chen group)

Multi-cycle femtosecond driving lasers can produce attosecond pulse trains through high order harmonic up-conversion processes, e.g. one cycle of driving laser field produces two attosecond bursts. The train structure of such attosecond pulses limits the experimental resolution to the order of femtoseconds rather than attoseconds due to undistinguishable attosecond events in the pulse trains. In order to achieve attosecond resolution, an intense motivation for the ultrafast community for a decade has a clear goal of a single isolated attosecond generation. Recently our IPT NTHU research team, collaborating with KMgroup in JILA, University of Colorado at Boulder, University of Delaware, and Universidad de Salamanca in Spain has achieved a breakthrough of finding a simple and very straightforward way for isolated single attosecond pulse generation, called phase-matching gating. The physical principle behind this process is that high harmonic generation always comes with an ionization process, a transition from neutral to plasma, which naturally creates a temporal refractive index ramp. Since a bright phase-matched attosecond pulse just happens at one specific refractive index, the generation process itself creates one very narrow phase-matching window, leading to single isolated attosecond pulse generation simultaneously. This mechanism works especially for a longer wavelength-driving laser. This new technique presents an accessible and reliable route to generate stable, isolated attosecond and makes it possible to capture the attosecond motion of electrons in a broader range of atoms, molecules, liquids, and materials.


Generation of isolated attosecond bright soft X-ray pulses driven by Multicycle midinfrared lasers. Ming-Chang Chen, Christopher Mancuso, Carlos Hernández-García, Franklin Dollar, Ben Galloway, Dimitar Popmintchev, Pei-Chi Huang, Barry Walker, Luis Plaja, Agnieszka A. Jaroń-Becker, Andreas Becker, Margaret M.Murnane, Henry C.  Kapteyn, and Tenio Popmintchev. PNAS, 2014 DOI: doi: 10.1073/pnas.1407421111 (2014) 

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