Spectroscopic Signatures of Plasmonic Near‐Fields on High‐Harmonic Emission

Abstract

AbstractIntense laser fields can reveal the attosecond and femtosecond response of matter in the emitted photoelectrons and high‐harmonic photons. The complementary perspective offered by these two messengers is well explored in gas molecules and, more recently, in bulk solids, where both electron emission and high‐order harmonics have been utilized to probe the laser‐matter interaction. In nanoscale solids, electron emission provides a wealth of information about the localized and inhomogeneous near fields around the nanoparticles. Here, it is shown experimentally that inhomogeneous fields also affect high‐order harmonics. Specifically, the experiment reveals strong indications that the field gradient of a nanoscale plasmonic hotspot found inside a Si crystal induces the emission of even‐order high harmonics from the crystal itself. This demonstration extends the complementary electron‐photon perspective on attosecond science to nanoscale systems.