World’s brightest laser pulses will create matter out of nothing – Prof. Wolfgang Sandner

Could you explain why light research infrastructure is important?

‘There are probably more than a hundred large laser research infrastructures in the world and there are more than 30 major national laser research infrastructures in Europe. One has to see it as a pyramid with all these infrastructures of various sizes, and even more principal investigator groups at the base, and ELI soon at the top, providing the world’s most powerful and most intense laser.

‘The ELI lasers produce up to 10 petawatts of power – this is a one with 17 zeros – more than a thousand times the power of all electrical power stations in the world. This power comes in extremely short time durations and the questions that we want to investigate are what are the unique and new phenomena in the interaction of such powerful light with matter.

‘For instance, we focus those beams onto solid surfaces which turn into plasma – a mixture of negative and positively charged constituents of matter – and this plasma emits extremely bright and powerful X-ray radiation. We will explore many ways of forming such radiation, which otherwise has only been created by very large or huge infrastructures through a completely different process. We expect our radiation to be much shorter, of higher quality and more brilliant in the sense that it can be much better focused and can give better images, for example of biological materials like proteins, for materials research, or for fundamental science studies.

‘So, the creation of X-ray secondary radiation is one of the main research areas and it is concentrated in the Hungarian and the Prague facilities, mostly. The Romanian facility, on the other hand, uses different laser-based methods to create even shorter wavelengths, so called Gamma rays, and will use them to study atomic nuclei in greater detail than ever before.

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‘We are entering areas where no-one has been before.’

‘One other application that we are trying to push forward with these extremely powerful lasers are new methods of particle acceleration. At the moment particle accelerators, as we know them from CERN (the European Organization for Nuclear Research) and many other laboratories worldwide, use radio frequency fields to accelerate particles. ELI together with quite a few other laboratories in the world will push forward the idea of laser plasma accelerators, using electrical fields for accelerating particles that are a thousand times stronger, or more, maybe much more, than in conventional particle acceleration. This is relevant as it overcomes a fundamental physical limitation that prevents conventional accelerators from moving to ever higher energies.’

What is the aim then of the ELI project? 

‘Clearly, the main aim is to do research with the technologies that we are developing and implementing. ELI will be the world’s first international user facility in the area of lasers, meaning that the research will mainly be done by international users that apply for beam time at any of the ELI facilities. They will bring their own ideas and research projects, and carry them through at ELI.

‘Fundamental science is the main mission of ELI and the breadth of research opportunities that ELI offers ranges from the secondary beams, as I mentioned, to particle acceleration, to nuclear physics and some medical applications. But, also some very fundamental questions about what happens if such high-power lasers are simply focused into the vacuum – the nothing. We expect to be able to create electron positrons out of the nothing, due to the enormous forces of our laser light.

‘Having said this, I should point out that the technological spin-offs and the socio-economic impact of the ELI facilities, being located where they are, in new Member States of the European Union, have been a crucial element in the decision to build ELI and are not to be forgotten.’

When will the ELI facilities be available for scientists to use?

‘The current plan, and we are well within our schedule, is that in the beginning of 2018 the construction will be finished to the extent that we will accept the first users. It will be a ramping up activity, so the number of users will increase over the following one or two years, but in 2018 we will start.’

How does the power of the lasers being developed at ELI compare with what is currently available to scientists worldwide?

‘Currently available are lasers of a power of one petawatt and there are less than a handful of them. The ELI lasers in all three facilities will be at least 10 times more powerful, but in addition, which is of equal importance, they will have considerably higher repetition rates than any of the currently available lasers of comparable power.’

You suggested that some of the applications of these lasers may overtake and supersede current large research infrastructures, but I assume that, given the power of the lasers, they must be large scale infrastructures themselves?

‘They are and I can explain, but let’s not misunderstand, we don’t plan to supersede or make the existing facilities irrelevant. On the contrary.

‘Without the existing facilities the world would not be able to sustain a user community that can make use of ELI. We need all the existing facilities – and there are more coming – that do experiments which don't require the top specifications of ELI. A user community that investigates light-matter interactions in all its aspects needs those complementary infrastructures in order to get a complete understanding of what happens in nature. ELI will only be able to support, simply for capacity reasons, those experiments and users that need the ultimate specifications in power, in repetition rate, beam quality etcetera.

‘Having said that, yes, the ELI facilities themselves are very large facilities. On the ELI website you can find live video coverage monitoring them and there you will see that these are extremely large buildings. Apart from the Megajoule Laser in Bordeaux (France) and the NIF laser in Livermore (US) they are probably the largest facilities of their kind in the world – all three of them.’

There is another large light infrastructure project being developed in Hamburg, the European XFEL research facility, how will this compare with ELI?

‘The XFEL is an X-ray free electron laser, which is an accelerator of the kind I described using radio frequencies. Electrons are accelerated along a three kilometre tube and at the end of the tube they are forced on to some wiggling trajectories, which causes them to emit very intense and bright X-radiation.

‘The power of those pulses is orders of magnitude lower than those of ELI lasers, but they are X-rays to begin with, and the repetition rate with which they are emitted is much higher than the repetition rate of the ELI lasers or secondary radiation.

‘ELI is working very closely with Hamburg and we view our facilities as very much complementary, so some users may go to XFEL when they need very high-repetition rates of X-radiation and they may go to ELI when they need much shorter pulses and better coherence than XFEL can provide.’

Can you give an example of the different research applications of those two different light pulses?

‘XFEL has always focused on its ability to provide X-radiation with such high intensity that you can take a picture of the structure of proteins in one shot, which is extremely important because if you were to illuminate proteins with more than one shot they would explode and blur the image. In addition, XFEL can provide these powerful X-ray pulses with a higher repetition rate. ELI, on the other hand, will produce shorter pulses, allowing the study of the motion of electrons inside atoms and molecules, and will have higher coherence and beam quality to get even more detailed information from the samples under study.’

This must be an exciting project to work on, what research are you particularly looking forward to?

‘ELI will provide us with the highest power that we can presently generate with a light source. If we focus that power we will produce power densities and electromagnetic forces that have never been applied before, to matter or to a vacuum. Whenever you have something new and you simply do the experiment the probability of finding something fundamentally new is rather high. For instance, we will be exploring quantum electrodynamics in regions where it could not be explored before.

‘Also, when we transform matter into new states of extremely high density and temperature, like in the interior of stars, we may create new qualities of secondary radiation and we may also be able to study matter under the sort of extreme forces, pressures and temperatures that we haven’t seen before.

‘For more practical applications, particle acceleration is a key technology that is not just important in fundamental research, but also in medicine, materials research and other science. We will explore new laser-based technologies along these lines. It is a very dynamic field at the moment, and we don’t yet know what the future of laser-based particle acceleration will be. But, we haven’t seen any road blocks so far and we expect it to be more or less a disruptive technology, so there will be new discoveries coming up that we don’t even consider at the moment.

‘So, in many respects, since ELI’s lasers are superlative in their specifications, the outcome will necessarily be new because we are entering areas where no-one has been before.’

Have you had much interest from scientists who would like to use the facilities?

‘Constantly. We are running user workshops and developing the first sets of experiments together with the international user community to make sure that we have very exciting new physics going on as soon as the facilities open.

‘We will probably start to collect specific applications from users once there is one year to go. But the users are already involved in the development of the facilities and they are actively contributing ideas, they are actually shaping the facilities as far as the scientific research opportunities are concerned.’

So, do you know what the first experiment performed at ELI will be?

‘No and there is a good reason why. Lasers and laser applications are developing so rapidly that it is very hard to predict three years in advance what will be the most exciting experiment. We have a few general ideas, which we are pursuing, but it will only be in the last year before operation of the facility that, based also on applications from users, we will make serious preparations for the first experiments.’