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Compact high-repetition-rate source of coherent 100 eV radiation


Coherently enhancing laser pulses in a passive cavity provides ideal conditions for high-order harmonic generation in a gas, with repetition rates around 100 MHz (refs 1,2,3). Recently, extreme-ultraviolet radiation with photon energies of up to 30 eV was obtained, which is sufficiently bright for direct frequency-comb spectroscopy at 20 eV (ref. 4). Here, we identify a route to scaling these radiation sources to higher photon energies. We demonstrate that the ionization-limited attainable intracavity peak intensity increases with decreasing pulse duration. By enhancing nonlinearly compressed pulses of an Yb-based laser and coupling out the harmonics through a pierced cavity mirror, we generate spatially coherent 108 eV (11.45 nm) radiation at 78 MHz. Exploiting the full potential of the demonstrated techniques will afford high-photon-flux ultrashort-pulsed extreme-ultraviolet sources for a number of applications in science and technology, including photoelectron spectroscopy, coincidence spectroscopy with femtosecond to attosecond resolution5,6 and characterization of components and materials for nanolithography7.

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Figure 1: Experimental set-up for intracavity HHG.
Figure 2: XUV output coupling mirror, fundamental beam profiles and calculated output coupling efficiency.
Figure 3: Intensity upper bound for uncompressed and nonlinearly compressed pulses.
Figure 4: Harmonic spectra and beam profiles.


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This work was supported by the Deutsche Forschungsgemeinschaft (DFG) Cluster of Excellence, Munich Centre for Advanced Photonics (MAP) (, by the KORONA Max-Planck-Institut für Quantenoptik (MPQ)/Fraunhofer-Institut für Lasertechnik (ILT) cooperation and by the Bundesministerium für Bildung und Forschung (BMBF) under PhoNa − Photonische Nanomaterialien (contract no. 03IS2101B).

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The project was planned by I.P., S.H., J.R., J.L., T.U., A.T., T.W.H., A.A., F.K. and E.F. The Yb:fibre laser was designed and built by T.E., J.L. and A.T. The piercing in the substrate for the XUV output coupling mirror was realized by D.E., J.W. and P.R. The HHG experiments and model development were performed by I.P., S.H., T.E., H.C., J.W. and E.F. All authors discussed the results and contributed to the final manuscript.

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Correspondence to I. Pupeza.

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The authors declare no competing financial interests.

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Pupeza, I., Holzberger, S., Eidam, T. et al. Compact high-repetition-rate source of coherent 100 eV radiation. Nature Photon 7, 608–612 (2013).

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