Strong-field coherent control at gold needle tips – published in Nanophotonics
In memory of Professor Mark Stockman, an exceptional theoretical physicist and dear colleague, we show in our recent publication that coherent control at nanotips made of the plasmonic material gold can be observed even approaching the strong-field region. In our experiment, photoelectrons are emitted from the tip by a two-color field. In energy-resolved electron spectra for strong and short driver pulses, we observe a plateau with high-energy cutoff, which is a clear indicator of field-driven dynamics and allows to estimate a near-field intensity of 4 TW/cm^2. Adding now the second harmonic of the fundamental field and changing the relative phase between these two colors, the emitted current can be modulated with a contrast of up to 80% in the strong-field region. These results are a further step towards combining concepts from strong-field physics, nanoplasmonics, and coherent control, all fields that were marked significantly by Mark Stockman.
In addition to controlling electrons at plasmonic structures, we show in this special issue that this is also possible within a solid, in this case graphene, using two-color fields.