attosecond – Progress in Research

Crucial discovery on the ultrafast charge injection in semiconductors

Posted on 13/09/202306/08/2024 by Erik Franco

The capability to follow and control ultrafast electron dynamics in matter with light pulses is a long-sought goal, with important implications in many fields of technology and research. In a semiconductor, for example, charge injection by few-femtosecond infrared pulses could be used to turn the material into a conductive state, realizing ultrafast switches in opto-electronics, a milestone that promises to increase the limiting speed of data processing and information encoding. This technological breakthrough can only stem from a comprehensive knowledge of light-induced charge injection, a key challenge of modern solid-state physics and photonics.

A study published in Nature Photonics tackles this problem by investigating field-driven carrier injection in a prototype semiconductor (monocrystalline germanium) with attosecond transient reflection spectroscopy: the researchers from Politecnico di Milano, in collaboration with the Istituto di Fotonica e Nanotecnologie (IFN-CNR), the Istituto per la microelettronica e microsistemi (CNR-IMM), the Istituto Nanoscienze (CNR-NANO) and a group from the Università degli Studi di Salerno, have discovered a new light-matter interaction regime where charges are excited by diverse coexisting mechanism. These mechanisms compete and develop on different time scales, of the order of few millionths of billionth of a second.

The researchers succeeded in disentangling the complex charge injection regime on these extreme temporal scales thanks to the experiments performed by the Attosecond Research Centerwithin the ERC project AuDACE (Attosecond Dynamics in AdvanCed matErials) and the PRIN project aSTAR. By means of simulations based on advanced theoretical models, they have shown the complex interaction between diverse mechanisms in the quantum-mechanical response of the material, never observed before, with important implications in many fields as optics, photonics, and information technology.

Those are significant results because the knowledge of the excitation processes induced by light in semiconductors allows us to design new opto-electronic devices with optimized ratio between charge injection speed and dissipated power.
Matteo Lucchini, professor of the Department of Physics and last author of the study

Read the study online

New, crucial information on the validity of the Floquet Theory applied to very short light pulses

Posted on 21/12/202206/08/2024 by Erik Franco

The Floquet Theory, particularly important for the development of new concepts in electro-optics, is used to create time crystals and induce new properties in materials. A study published in Nature Communications presents new, crucial information on the validity of this theory when applied to very short light pulses.

Researchers in the Department of Physics at the Politecnico di Milano, in partnership with the Institute of Photonics and Nanotechnology (IFN-CNR), the University of Tsukaba (Japan) and the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg (Germany), have discovered that a time crystal with unique properties can be induced even with very short pulses, lasting a few millionths of a billionth of a second, or femtoseconds.

The researchers managed to observe the creation of Floquet state of a free electron on this ultrashort time scale, thanks to experiments conducted at the Attosecond Research Center of the Department of Physics at the Politecnico di Milano as part of the ERC project AuDACE (Attosecond Dynamics in AdvanCed matErials). Using simulations based on advanced theoretical models, they demonstrated that the Floquet Theory can be extended to these regimes.

These are significant findings because the possibility to induce new properties in matter with ultrashort light paves the way to the realization of new devices, impossible to obtain with standard techniques.
Matteo Lucchini, professor from the Department of Physics and lead author of the study

What happens within molecules immediately after interaction with light?

Posted on 06/06/202111/10/2021 by admin

Tag: light-matter interaction, attosecond, Molecular electronics
Researcher: Mauro Nisoli
Department: DFIS – Department of Physics

Prof. Mauro Nisoli (Department of Physics, Head of the Attosecond Research Center at Politecnico di Milano), along with Fernando Martín (IMDEA and Universidad Autónoma de Madrid) and Nazario Martín (Universidad Complutense de Madrid), have been awarded an ERC Synergy Grant for the TOMATTO project (the ultimate time scale in organic molecular opto-electronics, the attosecond).

Researchers will explore what happens within individual molecules immediately after interaction with light. This is uncharted territory, since light triggers events that are not easily accessible, happening as they do in extremely short time scales, in the order of attoseconds. The goal here is to study and – possibly – control the light-induced motion of electrons in molecules with an unprecedented temporal resolution; researchers also aim to understand how the interaction with light is influenced by the molecular structure, in order to alter this structure according to a specific design.

This project brings together skills and competences from different research centers and universities. The research, coordinated by a team of experts in laser technologies, is the synthesis of new organic materials and computational methods. The team in Politecnico di Milano will focus on the experimental validation of theoretical work using latest generation instruments. The end goal is to engineer the molecular response to be able to produce materials with improved opto-electronic characteristics.

TOMATTO will be funded by an ERC Synergy Grant under the Horizon 2020 scheme and will receive almost 12 million Euro of funding over 6 years. Of these, 5 million will be allocated to Politecnico di Milano.