Electron ping pong in the nano world
An international team of researchers that included researchers from the Max Planck Institute of Quantum Optics and FOM Institute AMOLF has managed to control and monitor strongly accelerated electrons from nano spheres of silica with extremely short and intense laser pulses. The experiments and their theoretical modeling are described by the scientists in Nature Physics. The results open up new perspectives for the development of ultrafast, light-controlled nano-electronics, which could potentially operate up to one million times faster than current electronics.
When intense laser light interacts with electrons in nanoparticles that consist of many million individual atoms, these electrons can be released and strongly accelerated. The researchers report how strong electrical fields build up in the vicinity of the nanoparticles and release electrons. Driven by these electrical fields and collective interactions of the charges resulting from ionization by the laser light, the released electrons are accelerated, such that they can by far exceed the limits in acceleration that were observed so far for single atoms. The exact movement of the electrons can be precisely controlled via the electric field of the laser light. The new insights into this light-controlled process can help to generate energetic extreme ultraviolet (EUV) radiation.
Original publication
Controlled near-field enhanced electron acceleration from dielectric nanospheres with intense few-cycle laser fields, Nature Physics, 24. April, doi: 10.1038/NPHYS1983.
For further information, please contact
Marc Vrakking, groupleader AMOLF/MBI, m.vrakking@amolf.nl & marc.vrakking@mbi-berlin.de
Erny Lammers, AMOLF communication, e.lammers@amolf.nl, +31 (0)20 754 74 08.
More about this research
Ping pong
Electron acceleration in a laser field is similar to a short rally in a ping pong match: a serve, a return and a smash securing the point. A similar scenario occurs when electrons in nano particles are hit by light pulses. An international team was now successful in observing the mechanisms and aftermath of such a ping pong play of electrons in nano particles interacting with strong laser light-fields. The researchers illuminated silica nano particles with a size of around one hundred nm with very intense light pulses, lasting around five femtoseconds (one femtosecond is a millionth of a billionth of a second). Such short laser pulses consist of only a few wave cycles. The nano particles contained around fifty million atoms each. The electrons are ionized within a fraction of a femtosecond and accelerated by the electric field of the remaining laser pulse. After travelling less than one nano meter away from the surface of the nano spheres, some of the electrons can be returned to the surface by the laser field to the surface, where they were smashed right back (such as the ping pong ball being hit by the paddle). The resulting energy gain of the electrons can reach very high values. In the experiment electron energies of ca. sixty times the energy of a sevenhundred nm wavelength laser photon (in the red spectral region of light) have been found. For the first time, the researchers could observe and record the direct elastic recollision phenomenon from a nanosystem in detail.
EUV
The accelerated electrons left the atoms with different directions and different energies. The flight trajectories were recorded by the scientists in a three-dimensional picture, which they used to determine the energies and emission directions of the electrons. The electrons were not only accelerated by the laser-induced electrical field, which by itself was already stronger than the laser field, but also by the interactions with other electrons, which were released from the nano particles. Finally, the positive charging of the nano particle surface also plays a role. Since all contributions add up, the energy of the electrons can be very high.
The electron movements can also produce pulses of extreme ultraviolet light when electrons that hit the surface do not bounce back, but are absorbed releasing photons with wavelengths in the EUV. EUV light is of particular interest for biological and medical research. According to our findings, the recombination of electrons on the nano particles can lead to energies of the generated photons, which are up to seven-times higher than the limit that was so far observed for single atoms. The evidence of collective acceleration of electrons with nano particles offers great potential. From this may arise new, promising applications in future, such as light-controlled ultrafast electronics, which may work up to one million times faster than conventional electronics.