Demonstrating the dynamics of electron-light interaction originating
from first principle
New toolbox for the nano-optics allows the theoretical description to the highest accurate level possible

Date:
August 31, 2020
Source:
Kiel University
Summary:
Quantum-physical fundamentals can be studied particularly well by
the interactions between electrons and photons. Excited with laser
light, for example, the energy, mass or velocity of the electrons
changes. A professor has invented a new toolbox to extend the
theoretical description of electron-light interactions to the
highest accurate level possible.



FULL STORY ==========================================================================
With the highest possible spatial resolution of less than a millionth of a millimetre, electron microscopes make it possible to study the properties
of materials at the atomic level and thus demonstrate the realm of quantum mechanics. Quantum-physical fundamentals can be studied particularly
well by the interactions between electrons and photons. Excited with
laser light, for example, the energy, mass or velocity of the electrons changes. Professor Nahid Talebi from the Institute for Experimental
and Applied Physics at Kiel University has invented a new toolbox
to extend the theoretical description of electron-light interactions
to the highest accurate level possible. She has combined Maxwell and Schro"dinger equations in a time-dependent loop to fully simulate the interactions from first principles. Talebi's simulation allows it for the
first time to describe ultra-fast processes precisely in theory and to
map them in real-time without using adiabatic approximation. Recently,
she presented her results in the journal Physical Review Letters. In
the long term, they could help to improve microscopy methods as Talebi
is investigating in her ERC Starting Grant project "NanoBeam" funded by
the European Research Council.


==========================================================================
The ultrafast electron microscopy combines electron microscopy and
laser technology. Having ultrafast electron pulses, the dynamics of
the sample can be studied with femtosecond temporal resolutions. This
also allows conclusions about the properties of the sample. Due to the
further development of spectroscopy technology, it is now possible to
study not only atomic and electronic structure of the samples but also
their photonic excitations, such as plasmon polaritons.

For the first time the simulation depicts the process of the
interactions as a film in real-time However, the simulation of such electron-light-interactions is time-consuming and can only be carried out
with high-performance computers. "Therefore, adiabatic approximations and one-dimensional electron models are often used, meaning that electron
recoil and amplitude modulations have been neglected," explains Nahid
Talebi, Professor of Nanooptics at the Institute of Experimental and
Applied Physics (IEAP) and an expert in simulations. For the first time,
her new simulation shows the process of the electron-light interactions as
a film in real-time, describing the complex interactions to the highest accurate level possible.

In her toolbox, she has combined Maxwell and Schroedinger equations in
a time- dependent loop to fully simulate the interactions from first principles; therefore laying down the new field of electron-light
interactions beyond adiabatic approximations. Due to this combination,
Talebi was able to simulate what happens when an electron approaches
a nanostructure of gold that was previously excited by a laser. Her
simulation shows how the energy, momentum, and in general the shape
of the wave packet of the electron change for each moment of the
interaction. In this way, the full dynamics of the interaction caused by
both single-photon and two-photon processes are captured. Single- photon processes are important for example to model electron energy-loss and -
gain channels, whereas two-photon processes are responsible for modeling
the laser-induced elastic channels such as the diffraction phenomenon.

Particularly in her simulation, Talebi observed a pronounced diffraction pattern that originates from strong interactions between electrons and
photons based on the Kapitza-Dirac effect. This diffraction pattern
can have promising applications in time-resolved holography, to unravel charge-carrier dynamics of solid-state and molecular systems.

Further improving spectroscopy methods with ERC project "NanoBeam" "Our
toolbox can be used to benchmark the many approximations in theoretical developments, including eikonal approximations, neglecting the recoil, and neglecting two-photon processes." Talebi thinks. "Although we already have
made a great step towards electron-light interactions beyond adiabatic approximations, there is still room for further developments." Together
with her team, she plans to include a three-dimensional Maxwell-Dirac simulation domain to model relativistic and spin interactions. She also
wants to better understand the role of exchange and correlations during electron-electron interactions.

Another aim of Talebi is to utilize the insights from her theoretical
modelling to propose novel methodologies for coherent control and
shaping of the sample excitations using electron beams. With her project "NanoBeam" she intends to develop a novel spectral interferometry
technique with the ability to retrieve and control the spectral phase
in a scanning electron microscope to overcome the challenges in meeting
both nanometers spatial and attosecond time resolution. The project is
funded by an ERC grant from the European Research Council with about
1.5 million euros.

This study was funded by the European Union as part of the project
"NanoBeam" as "ERC Starting Grant" of the European Research Council (ERC).


========================================================================== Story Source: Materials provided by Kiel_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Nahid Talebi. Strong Interaction of Slow Electrons with Near-Field
Light
Visited from First Principles. Physical Review Letters, 2020; 125
(8) DOI: 10.1103/PhysRevLett.125.080401 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200831124206.htm

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