Attosecond emission dynamics in nonlinear photoemission from metal tips

The frequency comb technique permits to control the carrier envelope (CE) phase of few cycle laser pulses. Before its invention, nonlinear photoemission from solids in the optical tunneling regime was proposed as an ideal sensor for the carrier envelope phase. Here, emission only occurs when the potential barrier at the metal vacuum interface is bent down (quasi-static regime). Therefore the emission process is sensitive to the laser electric field of a short laser pulse and thus its CE phase. A first study of photoemission from a planar gold cathode revealed a weak modulation of the photocurrent with CE phase. In this work, the author focus low-power Ti:sapphire oscillator laser pulses with a duration of about 6 fs tightly onto a sharp tungsten tip and measure emitted electrons spectrally resolved. CE phase stabilized pulses was used to record electron spectra as a function of CE phase with 250pJ pulse energy. The CE phase-dependent modulation is very pronounced (up to 100%) in the depicted energy region and can be used to detect the CE phase and CE offset frequency.