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

• Published in: Nature photonics Vol. 7; no. 8; pp. 608 - 612
• Main Authors: Pupeza, I., Holzberger, S., Eidam, T., Carstens, H., Esser, D., Weitenberg, J., Rußbüldt, P., Rauschenberger, J., Limpert, J., Udem, Th, Tünnermann, A., Hänsch, T. W., Apolonski, A., Krausz, F., Fill, E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2013; Nature Publishing Group
• Subjects: 639/624/1020; 639/624/1106; Applied and Technical Physics; Coherence; Harmonic generations; Holes; Ionization; Lasers; letter; Nanostructure; Photons; Physics; Quantum Physics; Radiation sources; Spectroscopy; Ultraviolet radiation
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/nphoton.2013.156

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 resolution 5 , 6 and characterization of components and materials for nanolithography 7 . Spatially coherent 11.45 nm radiation is produced by outcoupling the harmonics of cavity-enhanced nonlinearly compressed pulses from a Yb-based laser through a pierced cavity mirror. This technique may lead to high-photon-flux ultrashort-pulse extreme-ultraviolet sources for use in a wide range of applications.