Abstract

The nanoscale localization of light aided by the plasmonic response of materials goes hand in hand with enhancing its oscillating electric field. In the vicinity of the antenna, the electric field of a nano-Joule laser pulse can become strong enough to convert the laser light into high order harmonics through an extremely nonlinear interaction with gas atoms that occupy the nanoscopic volume. However, previously reported plasmon-assisted high harmonics [1,2] are suspected to be fluorescence [3,4]. The problem seems to be (i) the small number of gas atoms that can occupy the nanoscopic volume and (ii) the low damage threshold of the plasmonic antennas [5]. Here we use monopole nano-plasmonic antennas to demonstrate plasmon-assisted high harmonic generation directly from the high-density crystalline substrate that hosts an array of antennas. Built on a silicon substrate, the low bandgap of silicon relative to the ionization potential of rare gas atoms allows harmonic emission at much lower intensities. Imaging the high harmonic radiation will allow nanometer and attosecond measurement of the plasmonic field, unveiling collective relaxation dynamics and field reshaping while opening a new path to XUV frequency combs.

© 2016 Optical Society of America