Surprise slow electrons are produced after intense lasers-clusters interactions

The discovery could explain why biomolecules are damaged.

Simulation of a laser-induced cluster explosion. Credit: Thomas Fennel
Simulation of a laser-induced cluster explosion. Credit: Thomas Fennel

Intense laser-cluster interactions were known to produce energetic ions and electrons. But now, scientists have produced slow, low-energy electrons using intense laser-cluster interactions.

A group of scientists from Imperial College London, the University of Rostock, the Max-Born-Institute, the University of Heidelberg and ELI-ALPS uncovered modest bunches comprising few of a thousand particles to ultrashort, intense laser beats. They found that the vast majority of the emitted electrons were very slow and were emitted with a delay compared to the more energetic electrons.

Lead scientist Dr Bernd Schütte, who performed the experiments at the Department of Physics at Imperial, said: “Many factors including the Earth’s magnetic field influence the movement of slow electrons, making their detection very difficult and explaining why they have not been observed earlier. Our observations were independent of the specific cluster and laser parameters used, and they help us to understand the complex processes evolving on the nanoscale.”

Whenever particles or clusters on the nanoscale (nanometers in size) are struck by intense laser beams, different marvels are produced, and most are well understood. In any case, the age of exceedingly charged particles has so far represented an enigma to analysts. This is because simulations predicted that electrons and ions would recombine, reducing the charge of the ions.

Here, electrons are released after the more lively electrons, a large number of the moderate electrons can get away from the cluster of atoms. As a result, it turns out to be significantly harder for the charged particles to discover accomplice electrons that they can recombine with, and a large number of them remain exceedingly charged.

Senior author Professor Jon Marangos, from the Department of Physics at Imperial, said: “Researchers have been studying the energetic emission of particles from laser-irradiated atomic clusters since the mid-1990s.

“What is surprising is that until now the much lower-energy delayed electron emission has been overlooked. It turns out that this is a very strong feature, accounting for the majority of emitted electrons, and may play a big role when condensed matter or large molecules of any kind interact with a high-intensity laser pulse.”

In order to properly understand the experimental observations, scientists simulated the interaction of the laser pulse with the cluster. They found that the slow electrons result from a two-step process, whose second step relies on a final kick that has so far escaped researchers’ attention.

Professor Thomas Fennel from the University of Rostock explained, “First, the intense laser pulse detaches electrons from individual atoms. These electrons remain trapped in the cluster as they are strongly attracted by the ions. When this attraction diminishes as the particles move farther away from each other during cluster expansion, the scene is set for the important second step.”

“Weakly bound electrons get their final kick to escape from the cluster when they collide with a highly excited ion. As such correlated processes are quite difficult to model, the computing resources from the North-German Supercomputing Alliance (HLRN) were essential in solving the puzzle.”

The study is published in Physical Review Letters.