Two-color coherent control in photoemission from gold needle tips – published in Journal of Physics B

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Photoemission of electrons from a metal surface driven by femtosecond laser pulses can be controlled when a small fraction of a second laser field of different color, here, the second harmonic of the strong driving pulses, is superimposed. In our recent publication we show that this coherent control scheme can be applied to needle tips made from the plasmonic material gold. We found that the electron emission can be enhanced or fully suppressed resulting in a current modulation with up to 96.5% visibility (contrast) similar to tungsten tips. The high contrast in the emitted current can be explained by the interference of three excitation quantum-pathways, consisting of different combinations of photons from individual colors. Combining two-color coherent control with plasmonic structures may allow tailored electron emission with highest optical nearfields caused by plasmon resonances or a spatial separation of the laser excitation from the electron emission.