Channel closing in strong-field photoemission from tip arrays

Abstract

Ultrafast photoemission is a promising avenue for the development of petahertz electronics. For such devices, identifying the precise emission mechanism and quantifying the local field strength at the emission site are of utmost interest. While this information can be extracted from electron energy spectra or the scaling of the emission rate with peak intensity, such measurements are not always technically feasible and a clear interpretation of the results can be challenging. Here, we demonstrate channel closing as a precision gauge for the local enhanced optical nearfield strength. Channel closings originate from a field-induced upshift of the vacuum level, which leads to a small decrease of the emission yield with increasing intensity. We report the first experimental observation of such channel closings in the photoemission rate from an array of nanometer-sharp gold tips. Our data are well matched by simulated yields, enabling us to precisely measure the local, field-enhanced optical nearfield at the tip array in situ. We expect this method to be a versatile diagnostic tool for the characterization of lightwave optoelectronic devices, as it suffices to measure currents only.