Lithuania is a country of lasers. This statement is not only heard in videos presenting Lithuania or in the context of world exhibitions, but is also reflected in the activities of companies operating here. It would not be so easy to find a scientific laboratory without a Lithuanian laser.
"In 2023 Nobel laureate in physics Anne L'Huillier, together with colleagues Ferenc Krausz and Pierre Agostini, were awarded for developing experimental methods that generate attosecond light pulses to study electron dynamics in matter. The researchers extracted these attosecond pulses using lasers we developed. The use of lasers developed by Lithuanian scientists in top-level scientific research once again proves the quality of Lithuanian lasers and the importance of the scientific research being developed", he is happy. Vilnius University (VU) Chief Researcher of the Laser Research Center of the Faculty of Physics dr. Arūnas Varanavičius.
We talk with the scientist about the reasons that led to the emergence of laser science at VU, the subtleties and possibilities of use of femtosecond and attosecond lasers, the importance of cooperation between science and business.
From academic tasks to commercial products
Back in 1992 VU scientists prof. Algios Petros Piskarskas, prof. Audriaus Dubietis and University of Bordeaux (France) scientist Dr. Gediminas Jonušauskas proposed and demonstrated parametric amplification of chirped pulses (eng. Optical parametric chirped-pulse amplification - OPCPA) methodology is currently a widely used method of obtaining intense laser pulses. However, for a long time the concept of parametric amplification of chirped pulses was only an academic achievement.
"Around 2005 Lithuanian laser technology companies "Šviesos konversija" and "Ekspla" have developed a new type of laser with exceptional parameters. The VU Laser Research Center came up with the idea of combining the lasers produced by these companies and creating a reliable compact laser source that could generate short pulses of a few femtoseconds in duration," the researcher recalls.
From timid experiments trying to combine lasers from several companies into a single system, everything turned into a rather broad topic of scientific research.
"Already at the initial stage of our research, companies fully supported our work carried out at the VU Laser Research Center. Later, companies got involved in these works, using their scientific, engineering, as well as financial potential. This allowed us to create a laser that has a versatile combination of exceptional parameters. At one time, it was the highest average power multi-optical cycle laser in the world," recalls the scientist.
The challenge of this millennium is attosecond systems
In order to better understand the intricacies of the femtosecond lasers developed by VU scientists, we should first understand the terms femtosecond and attosecond.
“A femtosecond is a million times shorter than a microsecond. And a microsecond is another million times shorter than a second. Let's compare: in one second, light can circle the Earth about seven times, while in a femtosecond, light travels only a fraction of a micron. Meanwhile, an attosecond is another thousand times shorter than a femtosecond. Attosecond signals are the shortest signals created by humans, and reliable systems generating attosecond pulses are one of the most important tasks of laser science today," the researcher presents.
Today, the VU Laser Research Center is developing femtosecond lasers, which can generate attosecond pulses using and applying special nonlinear optics methods.
"The lasers we are developing are not attosecond, but they create femtosecond optical pulses. Using accumulation sources and the method of high harmonic generation, the radiation is transferred to the deep ultraviolet or regen range, and there is already an opportunity to form attosecond pulses," says Dr. A. Varanavičius.
Femtosecond lasers were originally large and complex devices that required researchers with a Ph.D. Today, these are suitcase-sized devices that students learn to operate within a few working days.
"The development of attosecond lasers can be compared to the exploration of space and planets. We may not even dream of trips to the Moon or Mars until we go into Earth orbit, and a launch vehicle is needed to lift a spacecraft into Earth orbit. Returning to the example of lasers, the femtosecond lasers we are developing are, one might say, those "rocket carriers" that can allow scientists to move into the range of attosecond pulse generation," says the interviewer.
Attosecond lasers are already used today to study transformations in atoms and molecules. These processes are extremely fast, so very short-pulse lasers are needed to study them.
"We hope that in the near future, from data from attosecond lasers, we will be able to project 4D dimensional records that will have three dimensions of space and one dimension of time." In them, we will be able to clearly see how the transformations of molecules take place. Attosecond pulses in the X-ray range are highly needed in biological research and because of the "water window" that exists here. It has been established that light 2-4 nanometers long is not absorbed by water, so with very short laser pulses we can study what happens in the molecule of biological objects," says the scientist.
Lithuanian lasers help to carry out high-level scientific research
Extreme light infrastructure Extreme Light Infrastructure - ELI) is an analogue of the well-known CERN, only the work here is not carried out in the field of atomic physics, but in the field of lasers. This infrastructure consists of three large centers in the Czech Republic, Hungary and Romania.
"These centers are home to some of the world's best lasers for interdisciplinary collaboration. These are open access centers to which a scientist in any field, having a good idea and knowing that it requires extremely high-power lasers, can apply and get access," says the researcher.
Today, even three ultra-short pulse lasers developed by scientists from VU and Lithuanian laser companies are operating at the ELI center. These are relatively compact devices that fit into a regular-sized laboratory and are designed to be used by more than just physicists.
"I am really proud of the talent and ability of Lithuanian scientists to create such high-level production. This allows Lithuania to contribute to the development of lasers worldwide. When developing lasers, we try to ensure that they are useful for scientists in other fields, and that they are easy to operate not only for physicists, but also for specialists in other fields," says Dr. A. Varanavičius.
The future of lasers is controlled nuclear reactions and better cancer treatment
in 1992 prof. AP Piskarskas said that the technology of parametric amplification of chirped pulses can offer us pulses of terawatt power, and currently we already have petawatt lasers that are a thousand times more powerful. Such lasers can not only be applied to further fundamental scientific research, but also meet the needs of ecology, energy, medicine and other fields.
"One of the possible applications of high-power and high-speed lasers is nuclear fusion experiments. at the Livermore Laboratory. Lawrence Livermore National Laboratory - LLNL) researchers have been trying to find ways to control thermonuclear reactions with lasers for some time. At the end of last year, we received good news that the research results are promising and we are moving forward in this area," says the scientist.
High power lasers could also be used to accelerate subatomic particles. Already today we have calculations that high acceleration parameters can be achieved using high power lasers. Therefore, subatomic particle accelerators, whose dimensions today sometimes reach kilometers, can be reduced to the size of a laboratory.
"This opens up completely new opportunities in this area. Accelerators are used to generate directional streams of accelerated particles, all of which have potential applications in cancer therapy. Today, tests are carried out in which people with oncological diseases are led to an accelerator, where part of its radiation is directed to the affected organ. If we succeed in mastering the production of small accelerators, such equipment could become the standard equipment of medical institutions," observes Dr. A. Varanavičius.
in 2018 Nobel laureate Gerard Mourou raised the idea that high-power lasers can also be used in transmutation experiments of chemical elements.
"The results of these experiments are very promising as a way to decontaminate nuclear waste. Nuclear waste can be transformed into harmless elements by exposing it to laser radiation. Of course, scientific research in this field is still gaining momentum, but a lot of effort is being put into it," says the scientist.
Lithuania's success story: personalities, a harmonious ecosystem and properly directed funds
Dr. A. Varanavičius is happy to be able to observe the development of the laser ecosystem in Lithuania almost from the very beginning. According to him, personalities played a very important role here.
"We had Prof. AP Piskarskas, who, after returning from studies in Moscow, Vilnius University founded a laser school. He managed to find and attract really talented young scientists, some of whom went on to academic careers, while others left the university to start laser manufacturing companies. It's nice that the entire Lithuanian laser community maintains a close relationship to this day," says the interviewer.
Dr. While A. Varanavičius was still studying laser physics, there was certainly no shortage of young and enthusiastic specialists working in this field. Therefore, it is not surprising that at that time a number of priority laser physics researches were carried out, which had value not only in the then Soviet Union, but also throughout the world.
"An important role is also played by the first Lithuanian laser companies that were established approximately 30 years ago. This encouraged young people with an engineering background to study physics, because they knew that after completing their studies at the university, they would have an interesting job, they would be able to travel around the world installing laser systems, and they would receive a competitive salary," says the scientist.
The favorable attitude of the institutions became an incentive for the development of the field of lasers. The authorities initiated calls for projects and provided an opportunity to receive funds for expensive research.
"I'm glad that at that time the authorities appreciated the potential of the laser field and provided funding for our really expensive research. Of course, we later participated in international projects and became members of the "LaserLab Europe" network, which unites researchers in this field throughout Europe. This made it possible to build partnerships with scientists from other universities and contributed to the promotion of Vilnius University all over the world," says Dr. A. Varanavičius.
Dr. A. Varanavičius admits that, despite the competition between the university and companies for the most talented students, the most important thing is that young professionals choose the path that interests them.
"Partly, we face the problem that the most talented students do not stay at the university, and we seem to not secure a shift for ourselves. On the other hand, laser science is not left behind, because Lithuanian laser companies are already very strong and have their own scientific departments. Many doctors of science work in them, for whom the conditions have been created to continue conducting scientific research. Of course, such research is more applied in companies, since it is necessary to create a working product in a short time. Universities are freer from this point of view and the degree of risk here is higher," says Dr. A. Varanavičius.
