25 Interviews for the FNP’s 25th Anniversary: Grzegorz Soboń, PhD Eng., who works on lasers with graphene, talks to Aleksandra Stanisławska

Dodano: :: Kategorie: 25 years Foundation for Polish Science
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The Foundation for Polish Science (FNP) celebrates its 25th anniversary this year. To mark the occasion, we have invited 25 beneficiaries of our programmes to tell us about how they “practise” science. What fascinates them? What is so exciting, compelling and important in their particular field that they have decided to devote a major part of their lives to it? How does one achieve success?

The interviewees are researchers representing many very different fields, at different stages of their scientific careers, with diverse experience. But they have one thing in common: they practise science of the highest world standard, they have impressive achievements to their credit and different kinds of FNP support in their extensive CVs. We are launching the publication of our cycle; successive interviews will appear regularly on the FNP website.

Pleasant reading!

In the World of Lasers, Optical Fibres and Graphene

Grzegorz Soboń, PhD Eng., who works on lasers with graphene, talks to Aleksandra Stanisławska

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Photo: dr eng. Grzegorz Soboń, photo by OneHD

ALEKSANDRA STANISŁAWSKA: Lasers and optical fibres – many fans of science fiction must dream of working with such technical wonders. Is that where your choice of research area came from?

GRZEGORZ SOBOŃ: I have to disappoint you, but I don’t really like science fiction. And my encounter with lasers was largely accidental. When I was in my fourth year of studies at the Wrocław University of Technology, Prof. Krzysztof Abramski, one of my teachers at the time and later the supervisor of my doctoral dissertation, proposed that I join the Laser and Fibre Electronics Group that he headed, and to work on my master’s thesis there. I was happy to accept, and it turned out to be the best possible choice. Lasers have become my passion to such an extent that they fill my professional life. Frankly speaking, I don’t even have any defined hobby outside my job, something to devote myself to “after hours”.

Did you focus from the start on ultrafast fibre lasers with graphene? Even the name sounds great.

The subject of my research was also decided by a happy coincidence. Our research group had been working on fibre lasers and various aspects of laser optics for many years. I myself initially worked mainly on fibre amplifiers. Of course we’d heard of graphene, especially when Andre Geim and Konstantin Novoselov won the Nobel Prize in 2010 for discovering its properties. In 2011, together with my colleague from the group, Jarosław (Jarek) Sotor, I attended a conference in the United States that included a very interesting panel discussion on graphene, carbon nanotubes and other new materials for optoelectronics. This inspired us to conduct our own research. After returning to Poland, Jarek and I decided to obtain graphene ourselves using the same method as the Nobel Prize winners: by stripping away layers of graphite with sticky tape. And it worked the first time! We put the graphene in a laser and it worked as anticipated. If we hadn’t succeeded then, we most likely wouldn’t be talking today because we would have abandoned the problem.

How do the femtosecond lasers you build work?

In essence, they emit a series of equidistant, extraordinarily short pulses. Their duration is measured in femtoseconds, or thousand billionths of a second. Our first lasers generated pulses of a few hundred femtoseconds, now we easily get under 30 femtoseconds. Such properties are very important, for example, in laser-based micro-machining, because the time of interaction between the laser light and the material is extremely brief, so the material being processed is not heated – it is literally “evaporated”. The properties of such lasers work well not only in the processing of materials like semiconductors, metals and plastics, but also biological tissue. This last possibility opens the way to applications in medicine. The laser can be used as an optical scalpel in surgery, e.g. performed on the eye. We are already conducting such studies with ophthalmologists from the Medical University of Warsaw. We have also made the first attempts to produce a structure of the artificial heart valve leaflet surface that would stop haemoglobin from sticking to it, preventing blood clots. There are many more applications. Femtosecond lasers also work extremely well, for instance, in laser spectroscopy, detecting small concentrations of gases and molecules (e.g. carbon monoxide or methane) in the air. Since the optical spectrum generated by femtosecond lasers can be very broad, their application in spectroscopy enables us to build systems for the detection of many compounds simultaneously – contrary to systems utilizing continuous wave lasers.

What did graphene change in the lasers you build?

We use it in femtosecond lasers as a saturable absorber. It serves as a kind of passive “switch” that makes the laser emit very short light pulses. Graphene has interesting nonlinear optical properties. It periodically changes its capacity for absorbing light. Under normal conditions, e.g. in sunlight, graphene absorbs exactly 2.3 percent of light falling on it. That doesn’t seem a lot, but in fact it’s an impressive figure – remember that this is a material composed of a single layer of atoms. Meanwhile, in pulsed laser light it becomes almost transparent, then regenerates within a few dozen to a few hundred femtoseconds, and then the cycle is repeated. That’s why graphene placed in a laser makes the device emit very short pulses at even intervals that are shorter than in other materials used so far. However, this isn’t the only desirable feature of femtosecond lasers, because the emission wavelength is also important. Graphene is a broadband material, so – unlike semiconductors – it displays its unique properties for practically every light wavelength, from visible light all the way to mid-wave infrared. This means it can be used for building broadband optical frequency combs. A Nobel Prize was awarded also in this area, in 2005 to Theodor W. Hänsch and John Hall for developing optical frequency combs. In fact these are femtosecond lasers, in those days without graphene, appropriately stabilized and used for very accurate measurement of time and space. This is because a femtosecond laser generates pulses that are evenly spaced – in frequency terms, this corresponds to a spectral “comb”. A comb such as this constitutes a frequency standard, which is used e.g. by metrologists in optical atomic clocks, the world’s most accurate timepieces. Such clocks are just 1 second slow over about 30 million years. The lasers are also used for calibrating astronomical spectrographs that enable us to discover celestial objects outside the Solar System. I have seen estimates that ca. 90 percent of new planets discovered today can be observed thanks to optical combs precisely.

You were the first person in the world to build a fibre laser with a linearly polarized beam. What was the significance for the way the device works?

The laser’s structure maintaining linear polarization means that its operation is extremely stable, it has repeatable radiation parameters and is insensitive to external factors. This last element means that we can shake it, push it off the table, and it will continue to work. This is very important from the point of view of applications for the device outside a “sterile” lab. Under the GRAF-TECH programme of the National Centre for Research and Development, our team joined forces to build a few prototypes of this kind of laser with graphene. They were tested at different labs around the world and the repeatability of their parameters was confirmed there. One of our lasers is in permanent operation at the Institute of Electronic Materials Technology in Warsaw.

Is graphene the only material enabling such results to be achieved?

No, and that’s the most interesting thing. What we call topological insulators also work very well; these are two-dimensional materials of a layered structure with similar optical properties to graphene. Actually, this year (2016) the Nobel Prize in physics was awarded for discoveries in the field of topology. We are testing topological materials in our lasers as a substitute for graphene. Two-dimensional black phosphorus also looks promising in this respect. We have a few dozen such materials so far, and the list keeps growing. The main credit for this is due to graphene, because its discovery motivated scientists to look for other two-dimensional materials with graphene-like properties.

Are you still working on developing lasers?

Yes, though different ones than those I worked on before. The most recent world trend is to build lasers generating middle infrared radiation. This kind of laser enables ultrasensitive detection of chemical compounds, for example. This is because the absorption bands of all the most important molecules, e.g. greenhouse gases responsible for climate changes, are in the mid-infrared range. Hence, there is great demand for such lasers as well as sensitive systems for monitoring harmful emissions. That is why I went to Umeå University in Sweden where I will be working until April 2017 under a grant to develop a femtosecond system emitting middle infrared radiation for research related to extremely precise laser spectroscopy.

Wasn’t it possible to conduct such research in Poland?

Not this particular kind, but then this is a very unique field of knowledge in which just a few research groups in the world specialize, including the group from Umeå University. I even applied for funding for this kind of work in Poland, but unfortunately read in a review of my application that “optical combs have existed since 2005, so what’s the point of making them”. It turned out there was a group in Sweden that had received five-year funding for similar research, in the amount of several million kronor, and I was able to join them. I completed all my previous projects in Poland, mainly with funding from the National Science Centre, the National Centre for Research and Development and the Ministry of Science and Higher Education, which enabled our team to conduct world-standard research, though of course we realize that rival centres have much greater resources. Despite this, we proved it was possible to obtain globally unique results in Poland, and it is here that people want to come on research visits. As for me personally, individual support from the FNP in the form of the START stipend enabled me to focus on this specific research and facilitated my work on the project.

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Photo: dr eng. Grzegorz Soboń, photo by OneHD

You were a beneficiary of the START stipend twice.

Yes, that’s true, in 2013 and 2014. It’s worth mentioning that young Polish scientists consider this stipend to be the most prestigious, because it is awarded mainly on the basis of previous research achievements. So I am very proud, because not only did I receive the START stipend twice, but I received it the first time – as one of two beneficiaries – with a special commendation. This gave me strong motivation to continue working, because – let’s face it – I felt appreciated. But this support also had a purely financial side. When I received it for the first time, I was a PhD student. The second time around, I had obtained my PhD. The stipend guaranteed my upkeep for two years with a monthly sum that substantially exceeded a PhD student’s stipend, for example. This meant I didn’t have to worry about daily living – seek extra work outside research or decide on working in industry. I wanted to avoid that, because by then I was set on devoting as much of my time as possible to research. The support from the FNP really helped.

Is it hard to obtain grants in Poland for innovative research like yours?

It’s the most difficult to obtain support for the first project, when you cannot boast of any significant scientific achievements. After that it gets easier every time. Reviewers looked at me more favourably when I already had funding for research and could publish the results – I was able to do that also in prestigious scientific journals in the field of photonics, to mention Optics Express, Scientific Reports and Optics Letters. Once I could boast of my achievements before institutions distributing money to support research projects, a snowball effect occurred and further grants followed.

Do you have any professional dream that you haven’t managed to fulfil yet?

It is my dream to obtain stable financing to maintain my own research team. I’d like to form a real group for conducting research on currently relevant and interesting problems. I am especially interested in finding applications for the femtosecond lasers on which I worked before. I’d like to bring the project to the stage of real-term applications for these solutions, e.g. in laser spectroscopy. I try to gather students interested in this kind of research around me, and I “grab” them at a very early stage of their studies. In my time I set up a scientific club at the Wrocław University of Technology’s Faculty of Electronics, from which several people ended up pursuing PhD studies in our research group. I am an auxiliary supervisor of their doctorates (I don’t have a postdoctoral degree yet, so I cannot be a full supervisor). Having a grant from the National Science Centre, I am doing my best to keep these people with me for as long as possible. That’s how I’m forming the beginnings of my team. I hope I manage to obtain a grant enabling me to offer permanent employment to a few talented researchers. Maybe I’ll be able to take advantage of the Foundation’s help again and obtain funding for this from its TEAM or FIRST TEAM programmes. I failed the first time, but after returning to Poland I will definitely apply for such a grant again.

Do you feel fulfilled as far as scientific achievement is concerned?

Definitely not! I have a great many more goals and dreams. I probably share one of them with almost every scientist in the world: I’d finally like to publish a paper in a journal considered to be the most prestigious in its field, in this case Nature Photonics.

How is work progressing on the commercialization of your invention, namely the femtosecond laser with graphene?

It is still ongoing. We have the prototypes, and now we have to set up a spin-off company at the Wrocław University of Technology. We are checking our lasers’ usefulness for various applications, e.g. with the Medical University of Warsaw we are testing them in the field of eye surgery. I hope that also in Umeå they can be used in gas detection systems. I think we are well on the way to having our lasers finally end up at laboratories, companies and research centres all over the world.

GRZEGORZ SOBOŃ, PhD Eng., works at the Faculty of Electronics of the Wrocław University of Technology. He has twice been a beneficiary of the START programme (2013 and 2014), in 2013 winning the stipend with a special commendation received by the candidates that did best in the competition.