Technical University of Denmark: Laser researcher to build mini synchrotron system

A traditional synchrotron is an X-ray radiation facility built around a ring with a circumference of up to several hundred metres. High-energy X-rays are emitted by electrons that are accelerated inside the ring.

These days, many synchrotron systems are expanded with rings of different sizes and with different types of lasers to offer customers radiation with wavelengths from 1 picometre to 1 millimetre. Synchrotron radiation has been the basis of several Nobel Prizes and has a wide range of important applications in areas such as biology, physics, chemistry, materials research, medicine, pharmacology and geology.

Ole Bang is Professor and Head of the Fiber Sensors & Supercontinuum Group at DTU Photonics Engineering. He also works as a consultant in NKT Photonics and co-founded the companies NORBLIS and SHUTE Sensing Solutions, which are based on several of his own patents.

In addition, he is behind several groundbreaking achievements in laser and sensor technology, which have been described in articles in journals such as Nature Photonics.

Synchrotron facilities such as Max IV in Lund are large and expensive, and there are only a few of them. Professor Ole Bang wants to build a unique facility that is small enough to fit on a table. He has received a Villum Investigator grant for this project.

When researchers and companies investigate or develop new materials for use in everything from new solar cells and batteries to personalized medicine and hospital scanners, they use X-rays and ultraviolet radiation, among other things, and carry out measurements at one of the large synchrotron facilities in Europe. In addition to the trip, this requires a lengthy application process, so it’s not a simple thing to do.

When researchers and companies want to develop equipment and technologies to control pollution and food quality remotely, they need to use powerful mid-infrared light sources. These should preferably only be the size of a shoebox, but at the same time be able to cover an extremely wide spectrum of light – like the sun’s – in each light pulse. This type of equipment does not exist today.

However, Ole Bang, Professor at DTU Photonics Engineering, has an ambition to build just such a facility in mini-format – a so-called table-top radiation facility which consists of lasers and can be housed in a laboratory. And with a Villum Investigator grant of DKK 30 million, he is one step closer to being able to make his wild idea a reality.

“The plan is to develop four broadband lasers, so-called supercontinuum lasers, which together will cover the wavelength range from 15 micrometres right down to 33 nanometres and with a far greater light intensity than in the synchrotrons in Lund and Cern, for example, which otherwise are 50,000 times greater,” says Ole.

The aim is to give researchers and companies easier access to measuring materials using radiation within that particular wavelength range. Ole’s dream is to create a facility that companies and researchers can book to use. The longer-term goal is to develop the supercontinuum lasers, which will be small and robust enough to be used in hospital equipment to detect cancer, or in drones or helicopters to measure pollution.

“But it will take a lot of research to get to that point. Among other things, we need to develop new types of optical fibres the width of a human hair, which can conduct light with both ultra-short and ultra-long wavelengths. At the same time, we have to develop new laser technology and figure out how to control the powerful supercontinuum process. The latter will be a major research challenge,” Ole says.

There will be a strong focus on developing new materials and designing new fibres for lasers, which will contain the radiation. These will be developed in dedicated cleanroom laboratories at DTU Photonic Engineering.

In short, Ole Bang’s vision is very ambitious. The project will involve seven PhD students and four postdocs over the next six years.

Professor Ole Bang, Ph.d. Rasmus E. Hansen, forsker Chrisitan, Rosenberg Petersen. Foto: Jesper Scheel
Professor Ole Bang in the laboratory together with Ph.D. Rasmus E. Hansen and researcher Christian Rosenberg Petersen. Photo: Jesper Scheel.

Breaking world records
If Ole and his research team are to succeed in achieving their goal, they must break two different records along the way.

“One has to do with developing new optical fibres that can transport light in the mid-infrared spectrum. These have to be made from so-called soft glasses that melt at much lower temperatures than normal glass. This should help us break the record and keep the light concentrated in a beam right out to the predicted 15 micrometres.”

“Also, we need to develop fibre-based lasers whose fibres have a special structure around a hollow core that can contain a noble gas at high pressure. Imagine a hollow hair containing a gas at 50 bar. By pumping such a fibre with strong, short light pulses, we ionize the gas, which can thereby form light down to 100 nanometres. To reach the last bit down to 33 nanometres, we’ll break with traditional methods and develop a special metamaterial surface that’s put on the end of the fibre and forms light at a wavelength three times shorter than the light coming in. This will be a huge but exciting challenge,” says Ole.

Professor Ole Bang is among the ten selected researchers to be awarded the title of Villum Investigators in 2021. The Villum Investigator programme allows some of the world’s best researchers to freely pursue their best and most resource-demanding ideas with ample funding of DKK 20-40 million, normally over six years.

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