Strong-Field-Assisted Measurement of Near-Fields and Coherent Control of Photoemission at Nanometric Metal Tips

Metal nanotips are an ideal testbed for ultrafast and strong-field physics at solids due to the superb control they allow over their very apex and the near-field at this apex that enhances an incident laser field. Particular attention has recently been devoted to the study of laser-induced electron emission from nanotips, where an enhanced fundamental understanding contributes to the implementation of nanotips as a source of femtosecond electron pulses. In this chapter we present photoemission studies at nanotips illuminated with femtosecond lasers. We demonstrate a new technique to measure the strength of near-fields at nanostructures by using our knowledge of the occurring strong-field physics. Electrons rescattering with the surface of the nanotip after emission give access to the prevalent near-field intensity on the nanometer scale. Our measurements fit well with independent simulations of Maxwell’s equations. In the second part we show that by employing a synthesized light field of a fundamental and a second harmonic laser pulse we achieve almost perfect coherent control of the photoemission process. We demonstrate that we can interpret our findings in terms of interfering quantum pathways.