In order to make electronic devices faster and more powerful in the future, new and innovative approaches to controlling electrical signals must be explored. With the investigation of the ultra-fast emission of electrons from so-called plasmonic nanostructures, the Nanooptics group of the Institute of Physics is researching in this direction. Like two previous works, the results achieved in cooperation with the Wigner Research Center in Budapest have been published in the renowned Nano Letters.
By resonantly exciting their conduction electrons, plasmonic nanostructures amplify an incident light field and concentrate it into spatial regions that correspond to fractions of the light wavelength. This not only enables the photoemission of an electron, this electron is also strongly accelerated by the plasmonic field. This is easily detectable by spectroscopic measurements of the electron energy. The high light intensities required are achieved by laser pulses with durations of a few femtoseconds, which also enables ultra-fast control of the processes.
The precise analysis of the experimental electron spectra, together with a quantum mechanical description, turned out to be the key to understanding the hitherto unclear respective contributions of two photoemission mechanisms. On the one hand, an electron can absorb the energy required for emission by absorbing several photons. On the other hand, the incident light field can lead to tunnel emission of the electron. In fact, both effects occur together for light intensities relevant to measurement and potential applications. The understanding of the underlying mechanisms that has now been gained not only clarifies a fundamental question, but also enables the targeted use of the effects for future applications.
Béla Lovász, Péter Sándor, Gellért-Zsolt Kiss, Balázs Bánhegyi, Péter Rácz, Zsuzsanna Pápa, Judit Budai, Christine Prietl, Joachim R. Krenn, Péter Dombi, Nonadiabatic Nano-optical Tunneling of Photoelectrons in Plasmonic Near-Fields, Nano Letters 22, 2303–2308 (2022)