Megahertz high harmonic generation


Enhancement cavity


Our enhancement cavity CALDERA, tailored to your setup, supports both continuous-wave and multi-kW-level average power pulsed operation. Its applications include generating coherent vacuum-/extreme-ultraviolet (XUV) radiation at repetition rates of several 10s of MHz.

In the femtosecond enhancement cavity, a pulse train with MHz repetition rate coherently couples to a passive optical resonator via a partially transmitting input coupler. This results in a circulating pulse with significantly increased power. By focusing this intracavity pulse onto a gas target, we can create coherent XUV radiation at repetition rates of several tens of megahertz. This high-energy coherent XUV radiation serves various precision metrology applications in both time and frequency domains.

Key Product Features

  • State-of-the-art broadband cavity optics
  • Ready for average powers on the 100-kW level
  • Advanced designs tailored to specific applications
  • Stable operation at repetition rates ≥ 10 MHz


[1] Extreme-ultraviolet frequency combs for precision metrology and attosecond science
I. Pupeza, C. Zhang, M. Högner, J. Ye
Nature Photonics 15, 175 (2021)

[2] High-Flux, Ultrafast Extreme-Ultraviolet Photoemission Spectroscopy at 18.4 MHz Pulse Repetition Rate
T. Saule, S. Heinrich, J. Schötz, N. Lilienfein, M. Högner, O. de Vries, M. Plötner, J. Weitenberg, D. Esser, J. Schulte, P. Rußbüldt, J. Limpert, M. F. Kling, U. Kleineberg, I. Pupeza
Nature Communications 10, 458 (2019)

[3] Megawatt-scale average-power ultrashort pulses in an enhancement cavity
H. Carstens, N. Lilienfein, S. Holzberger, C. Jocher, T. Eidam, J. Limpert, A. Tuennermann, J. Weitenberg, D.C. Yost, A. Alghamdi, Z. Alahmed, A. Azzeer, A. Apolonski, E. Fill, F. Krausz, I. Pupeza
Optics Letters 39, 2595 (2014)