Providing tools for lighting up new horizons

Nobel Prize winner Prof. Gérard Mourou pushed a black button, and femtosecond laser pulses, each featuring ~6.6 fs duration, ~35 mJ energy, and running at 1 kHz repetition rate, were registered and visualized by a projector in front of a big audience. Thus the Single Cycle Femtosecond high intensity laser system SYLOS has been successfully launched in ELI-ALPS facility in Szeged, Hungary.

It [High intensity laser systems] is mostly applied in the fields of science, but can also have many applications for the needs of the society, for example, in laser vision correction surgeries. We basically have an ideal scalpel – with impulses so short we can cut the eye tissue with extreme precision. We can also accelerate the particles, accelerate the electrons. It is mostly applied in physics, but can also be applied in medicine, for example, in treating cancer.

Prof. Gérard Mourou
at SYLOS launch ceremony. Photo credit: ELI-ALPS

THE CHALLENGE

People have long dreamed of replacing one chemical element with another. In the middle ages, along with attempts to convert lead to gold, alchemists purified and researched many materials. In the modern age, myriad scientists at universities and other institutions work tirelessly to create new materials, discover new chemical elements, and probe basic properties of the world around us. Each study that probes deeper into the materials pushes the understanding of molecular and atomic structure and dynamical processes. In the six decades since the invention of the laser, the laser has been used to probe material properties.

Need for probing even deeper arose when research of nucleons and their component quarks or vacuum dissociation began. Beyond fundamental research, many high intensity laser applications arose, such as understanding of aging nuclear reactor materials, development of new methods for nuclear waste processing, medical and biomedical imaging, and even improvements of oncology treatment.

ELI-ALPS

For these tasks laser systems of much higher peak intensities were needed. A new type of large-scale laser infrastructure specifically designed to produce the highest peak power and intensity was established by the European Community: the Extreme Light Infrastructure (ELI). ELI was designed to be the first exawatt class laser facility, delivering kJ of energy over 10 fs.

The facility is based on four sites. Three of them are implemented in the Czech Republic, Hungary, and Romania.

ELI-ALPS is one of ELI facilities based in Szeged (Hungary). It will further deepen the knowledge of fundamental physics by providing high repetition rate intense light pulses in attosecond timescale. The main technological backbone of ELI-ALPS is optical parametric chirped-pulse amplification (OPCPA) of few-cycle to sub-cycle laser pulses.

Pumped by dedicated solid-state short pulse (ps-scale) sources and their harmonics, this approach prevails compared with conventional (Ti:Sapphire laser based) femtosecond technology in terms of pumping efficiency, contrast, bandwidth, and – as a consequence – degree of control of the generated radiation.

SYSTEM DESCRIPTION

The Single Cycle Laser SYLOS2A, which employs OPCPA technology developed at Vilnius University, has been designed and manufactured by a consortium of two Lithuanian companies – Ekspla and Light Conversion.

The consortium won SYLOS2A procurement tender in 2014. The system was installed on 15th May 2019 and produces Carrier Envelope Phase (CEP) stabilized, 6.6 fs laser pulses with a peak power of >5 TW and average power of 35 W at 1 kHz repetition rate.

The system consists of a frontend based on cascaded parametric amplifiers and employing passive CEP stabilization, driven by an industrial-grade femtosecond Yb:KGW laser, a diode-pumped Nd:YAG picosecond pump laser and 4 picosecond OPCPA stages, preceded by a seed pulse stretcher and followed by a compressor.

System reached parameters that were never seen before in this type of system. With peak power of > 5 TW at 1 kHz it enabled to step into new types of research with fast data acquisition and statistics gathering, which were previously not possible due to the lack a of suitable radiation source. It also obtained the best carrier-envelope phase (CEP) stability among systems of a similar class. Such CEP stability allows precise control of the laser-induced processes.

„By employing reliable and industry-tested technologies, the system is cost-effective, reliable, and can be easily maintained and upgraded. Some lower-power, cost-effective systems can be built based on the current development. System usage is cheaper and more convenient as the industrial modules are easier to manufacture and replace“ – noted Donatas Lengvinas, senior engineer in the high intensity laser group at Ekspla.

By employing reliable and industry-tested technologies, the system is cost-effective, reliable, and can be easily maintained and upgraded. Some lower-power, cost-effective systems can be built based on the current development. System usage is cheaper and more convenient as the industrial modules are easier to manufacture and replace.

Donatas Lengvinas
Senior engineer in the high intensity laser group at Ekspla

System monitoring and control at different amplification stages was implemented. Dedicated software accumulates, sorts, and represents the changes of main parameters over time. This allows diagnosis and adjustment of almost all parameters extremely quickly and without physical intervention of the system. A sophisticated self-diagnostic system allows hands-free operation and output specification stability all day long without operator intervention.

Unlike other systems on the market, reliable industry-tested technologies and components were employed to obtain a unique combination: extreme parameters, user friendliness, reliability, cheaper and more convenient maintenance and serviceability. During the implementation phase and subsequent trial period, the laser system demonstrated outstanding performance and reliability while it was running for 6 months, at least 8 hour a day.

“One of our most important aspect is reliability. SYLOS was planned to be versatile as possible, it drives five beamlines, the highest number at ELI-ALPS. The high demand means that we want to minimize downtime as much as possible. SYLOS not only deliver state-of-the-art laser parameters, but works like clockwork every day and we are certainly very satisfied with it.” – Adam Borzsonyi, Head of Laser Sources Division, ELI-ALPS.

NEW HORIZONS

„Nuclear waste remains radioactive for millions of years. Now we are hiding it deep in the ground, but there is one elegant way to get rid of these – we can transmute it. Exposed to appropriate laser radiation, nuclear decomposition half-life reduces from thousands, millions of years to hours or even minutes“ – mentioned Gérard Mourou, the 2018 Nobel laureate in Physics.

“Currently, the disposal of nuclear waste is comprised of either storing the waste in containers on above-surface level or burying them underground, depending on the decay period of the radioactive material. This method is raising safety concerns, as some of the waste is disposed not too far from densely populated areas, and highly radioactive waste has to be safely stored for up to tens of thousands of years,” said Dr. Artūras Plukis, Head of Experimental Nuclear Physics Laboratory at the Center for Physical Sciences and Technology in Vilnius, Lithuania.

High intensity powerful laser system opens the way for the investigations of nonlinear extreme ultraviolet and x-ray processes, four-dimensional imaging, as well as various industrial, biological and medical applications.

„It [High intensity laser systems] is mostly applied in the fields of science, but can also have many applications for the needs of the society, for example, in laser vision correction surgeries. We basically have an ideal scalpel – with impulses so short we can cut the eye tissue with extreme precision. We can also accelerate the particles, accelerate the electrons. It is mostly applied in physics, but can also be applied in medicine, for example, in treating cancer.“ – said Prof. Gérard Mourou.