We show that a significant enhancement of the photon flux produced by high harmonic generation can be obtained through guided configuration at high laser intensity largely above the saturation intensity. We identify two regimes. At low pressure, we observe an intense second plateau in the high harmonic spectrum in argon. At relatively high pressure, complex interplay between strongly time-dependent ionization processes and propagation effects leads to important spectral broadening without loss of spectral brightness. We show that the relevant parameter for this physical process is the product of laser peak power by gas pressure. We compare source performances with high harmonic generation using a gas jet in loose focusing geometry and conclude that the source developed is a good candidate for injection devices such as seeded soft x-ray lasers or free electron lasers in the soft x-ray range.
© 2014 Optical Society of America
Original Manuscript: March 24, 2014
Revised Manuscript: May 12, 2014
Manuscript Accepted: May 13, 2014
Published: June 18, 2014
Kevin Cassou, Sameh Daboussi, Ondrej Hort, Olivier Guilbaud, Dominique Descamps, Stéphane Petit, Eric Mével, Eric Constant, and Sophie Kazamias, "Enhanced high harmonic generation driven by high-intensity laser in argon gas-filled hollow core waveguide," Opt. Lett. 39, 3770-3773 (2014)