Light reflecting from a stationary mirror keeps its basic properties. However, more than a century ago, Albert Einstein asked what would happen if the mirror moved at a speed close to the speed of light. As a conventional mirror is not suitable for this, a nonconventional mirror is needed to answer this question. For example, a special mirror that uses a laser process.
The fabrication and control of so-called relativistic electron mirrors remains a huge challenge despite the dynamic development of high-intensity, ultrashort pulse laser technology in recent decades. In an article published in the journal Ultrafast Science, our physicists reported on a novel method. The work was carried out in collaboration between ELI ALPS and Pasqal Quantum Computing Company (Palaiseau, France). The members of the research group were Mojtaba Shirozhan, PhD student at ELI ALPS; Fabien Quéré, Director of the IOGS-CNRS-Pasqal Joint lab; and Subhendu Kahaly, Head of the Secondary Sources Division at ELI ALPS.
“By sculpting the driving waveform, we can strip and synchronously accelerate electrons from an ultrathin target into a single, dense, relativistic sheet acting as a mirror that compresses femtosecond light into an isolated attosecond XUV flash,” said Subhendu Kahaly. This is exciting for our institute because if we succeed in creating these mirrors, they will be able to condense a tailored incoming femtosecond laser pulse into ultra-intense extreme ultraviolet (XUV) attosecond pulses with controlled properties.
Mojtaba Shirozhan and Subhendu Kahaly
Using computer simulations, the group presented a new method that creates single, dense, relativistic electron sheets that can be used for generating isolated attosecond pulses in the extreme ultraviolet (XUV) range. The new approach uses coherent Thomson scattering from a single, dense, relativistic electron layer (RES), which acts as a relativistic mirror. When a few-cycle pulse propagating in the opposite direction is reflected from this mirror, it is compressed into an intense attosecond pulse. In other words, femtosecond light can be compressed into explosive XUV flashes.
According to Subhendu Kahaly, the robustness of the proposed concept is very important for its experimental feasibility and applications: “Our team used large‑scale simulations that include realistic laser waveforms and plasma dynamics, and we identified parameter ranges and tolerances that are compatible with current or near‑term high‑intensity laser facilities.”
With rapid advances in laser technology and targetry, the team expects proof‑of‑principle experiments at advanced laser facilities in the foreseeable future. When realized, the technique would provide a powerful new tool for attosecond science, high energy science and high‑field XUV applications.
Photos: Gábor Balázs