Two-color coherent control in photoemission from gold needle tips

TL;DR

This paper demonstrates coherent control of photoemission from gold needle tips using a two-color laser field, achieving high contrast modulation and analyzing the quantum pathways involved.

Contribution

It introduces a method to control photoemission via two-color laser fields and elucidates the quantum pathways affecting the emission process.

Findings

Achieved up to 96.5% modulation contrast in photocurrent

Identified three interfering quantum pathways in photoemission

Simulations confirm the pathway interference and control mechanisms

Abstract

We demonstrate coherent control of photoemission from a gold needle tip using a two-color laser field. The relative phase between a fundamental field and its second harmonic imprints a strong modulation on the emitted photocurrent with up to 96.5 % contrast. The contrast as a function of the second harmonic intensity can be described by three interfering quantum pathways. Increasing the bias voltage applied to the tip reduces the maximum achievable contrast and modifies the weights of the involved pathways. Simulations based on the time-dependent Schr\"odinger equation reproduce the characteristic cooperative signal and its dependence on the second harmonic intensity, which further confirms the involvement of three emission pathways.