Plasmon-enhanced high-harmonic generation from silicon

Plasmonic antennas can enhance the intensity of a nanojoule laser pulse by localizing the electric field in their proximity(1). It has been proposed that the field can become strong enough to convert the fundamental laser frequency into high-order harmonics through an extremely nonlinear interaction with gas atoms that occupy the nanoscopic volume surrounding the antennas(2-4). However, the small number of gas atoms that can occupy this volume limits the generation of high harmonics(5-7). Herewe use an array of monopole nano-antennas to demonstrate plasmon-assisted high-harmonic generation directly from the supporting crystalline silicon substrate. The high density of the substrate compared with a gas allows macroscopic buildup of harmonic emission. Despite the sparse coverage of antennas on the surface, harmonic emission is ten times brighter than without antennas. Imaging the high-harmonic radiation will allow nanometre and attosecond measurement of the plasmonic field(8) thereby enabling more sensitive plasmon sensors(9) while opening a new path to extreme-ultraviolet-frequency combs(10).