Lightwave Electronics at Sharp Metal Tips

Photo: A metal tip irradiated with a laser pulse

The steering of electrons with the electric field of well-controlled femtosecond laser pulses makes it possible to resolve atomic processes on an attosecond time scale. The independent Research Group Ultrafast Quantum Optics of Doctor Peter Hommelhoff has now applied this method to solid state surfaces, for example, to extremely sharp metal tips.

This way the scientists were able to show that comparable small laser intensities are sufficient to steer the emission of electrons from the metal tip with the phase of the optical cycle. The modulation observed in the resulting energy spectrum can be explained with the occurrence of a phase dependent coherent interference of electron wave packets, in agreement with numerical calculations.

As the tip is extremely sharp, having a curvature radius of about ten nanometres only, the intensity of the laser light gets greatly amplified. With this, relatively weak laser pulses are sufficient to set free electrons from the metal surface. Because of their short duration the laser pulses contain a few cycles only. Therefore the electric field acting on a particular electron is strongly dependent on the phase shift of the carrier wave relative to the envelope of the pulse.

For the first time the physicists have succeeded in the steering of electrons emitted from a solid state by the field of a femtosecond laser pulse. Even more, much less intensity was required compared to experiments with electrons in atomic or molecular gases. On the one hand, the new method is an important tool for gaining insight into the dynamics of electrons in solid state surfaces.

On the other hand, because of the low laser intensities required, there is a high potential for practical applications. Combining a metal tip, a retardation grid, and an electron multiplier, compact devices for the measurement and stabilization of phases of laser pulses could be realized. Also the development of optical field effect transistors can be envisaged in which the electric current can be switched on and off by the light field with attosecond precision.; Source: Max Planck Institute of Quantum Optics