Optimization and phase matching of fiber-laser-driven high-order harmonic generation at high repetition rate.

High-repetition-rate sources are very attractive for high-order harmonic generation (HHG). However, due to their pulse characteristics (low energy, long duration), those systems require a tight focusing geometry to achieve the necessary intensity to generate harmonics. In this Letter, we investigate theoretically and experimentally the optimization of HHG in this geometry, to maximize the extreme UV (XUV) photon flux and improve the conversion efficiency. We analyze the influence of atomic gas media (Ar, Kr, or Xe), gas pressure, and interaction geometries (a gas jet and a finite and a semi-infinite gas cell). Numerical simulations allow us to define optimal conditions for HHG in this tight focusing regime and to observe the signature of on-axis phase matching. These conditions are implemented experimentally using a high-repetition-rate Yb-doped fiber laser system. We achieve optimization of emission with a recorded XUV photon flux of 4.5×10(12) photons/s generated in Xe at 100 kHz repetition rate.

[1]  Philippe Balcou,et al.  Spatiotemporal separation of high harmonic radiation into two quantum path components , 1999 .

[2]  C. Spielmann,et al.  Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases , 2010 .

[3]  L. A. Lompré,et al.  Multiple-harmonic conversion of 1064 nm radiation in rare gases , 1988 .

[4]  D. Garzella,et al.  OPTIMIZING HIGH HARMONIC GENERATION IN ABSORBING GASES : MODEL AND EXPERIMENT , 1999 .

[5]  Anne L'Huillier,et al.  High-order harmonic generation with μJ laser pulses at high repetition rates , 2012 .

[6]  Catherine M. Herne,et al.  Phase matching of high-order harmonics in hollow waveguides , 1999, 2404.00071.

[7]  D. Ros,et al.  Pressure-induced phase matching in high-order harmonic generation , 2011 .

[8]  Tino Eidam,et al.  Power scaling of a high-repetition-rate enhancement cavity. , 2010, Optics letters.

[9]  Jun Ye,et al.  Direct frequency comb spectroscopy in the extreme ultraviolet , 2011, Nature.

[10]  Charles K. Rhodes,et al.  Studies of multiphoton production of vacuum-ultraviolet radiation in the rare gases , 1987 .

[11]  L'Huillier,et al.  Coherence control of high-order harmonics. , 1995, Physical review letters.

[12]  F. Krausz,et al.  Ultrabroadband efficient intracavity XUV output coupler. , 2011, Optics express.

[13]  Herbert Walther,et al.  High-order harmonic generation at a repetition rate of 100 kHz , 2003 .

[14]  Jens Limpert,et al.  High-order harmonic generation at a megahertz-level repetition rate directly driven by an ytterbium-doped-fiber chirped-pulse amplification system. , 2009, Optics letters.

[15]  J. Rothhardt,et al.  Generation of µW level plateau harmonics at high repetition rate. , 2011, Optics express.