High‐harmonic generation with plasmonics: feasible or unphysical?

High-harmonic generation (HHG) provides for efficient and coherent XUV generation for a wide range of spectroscopic applications, enabling attosecond spectroscopy, ultrafast photo-emission spectroscopy, or ultrahigh spatial resolution imaging [1]. Conventionally HHG is based on the use of high power amplified femtosecond laser pulses, special phase matching techniques, or intra-cavity field enhancement. As a compelling alternative, resonant plasmonic field enhancement in metallic nanostructures has been proposed to achieve the necessary peak intensity for HHG. Using nJ pulses from a Ti:S oscillator, XUV generation attributed to plasmon-enhanced HHG was reported in 2008 by the group of Seung-Woo Kim from KAIST in Daejeon, Korea, first in Ar [2] and later