First step towards an x-ray laser in Sweden

Richard Feynman, in his famous 1959 lecture “There’s Plenty of Room at the Bottom”, envisioned the opportunities that increasingly better electron microscopes would bring towards the advancement of our fundamental understanding of nature, and the possible development of nanotechnology. Feynman’s insight was correct, and both science and technology have truly developed towards nanoscale dimensions in the now almost 60 years that have followed his lecture. What even Feynman could not imagine, however, was the development not of electron-based, but of photon-based techniques that could look not only at the very small, but also at the very fast, allowing for scientists to explore the fundaments of nature.

Why is the very fast world (often referred to as “ultrafast”) interesting? It has to do with the characteristic time scales of atomic and electronic motion. Intuitively, and classically, the smaller the object (which often means the lighter), the faster it can move. It has to do with the law of inertia: the smaller the mass, the more an object can be accelerated by a given force. Using quantum mechanics, and in particular the generalised Heisenberg’s indetermination principle, one can estimate the order of magnitude of this time scale. For energies of the order of 1 electronVolt (1 eV is approximately 1.6 x 10-19 J), the typical energies associated with electronic processes, Heisenberg tells us that the fastest processes can take place on the femtosecond time scales (1 fs = 10-15 s).

Photo: Roger Eriksson, ESS

This incredibly small time scale from the experience of our everyday lives, is actually routinely accessed with commercial laser systems that in the past two decades have become available in modern physics laboratories around the world. However, while the time-scale is not a problem for these lasers, the spatial scale is. They typically operate in the visible or near-infrared range, meaning that their wavelength is approximately 1000 times larger than the typical spacing between atoms in a material. Since the wavelength is closely related to the minimum spatial resolution it is clear that atomic scales cannot be resolved. One needs x-rays, which have a much shorter wavelength, to achieve this. X-rays are also nowadays easily available at synchrotron light sources (the world’s brightest now MaxIV in Lund), but unfortunately, they cannot be produced in femtosecond bursts at those facilities.

Fotograf Leif Jansson
MAX IV exteriört sommar skymning ljuskonst

Almost serendipitously, a scientific revolution took place just a few years ago. In 2009, a new type of light source that combines both short wavelength and ultrafast, coherent femtosecond pulses, a real x-ray laser, was built at SLAC National Accelerator Laboratory in California. The video here explains how such a source works:

The peak brilliance of this instrument is 10 billion times larger than the one at the best existing synchrotron, allowing for experiments that were thought impossible even in many scientists’ wildest dreams. We can now look at how atoms, molecules, spins, move in real time and space, and are able to take a peek at how nature really works at the bottom. We can see how many physical, chemical and biological processes evolve at their intrinsic temporal and spatial scales in great detail. Already many breakthroughs in our understanding of nature have occurred thanks to these instruments, and many more are likely to happen in the future. There are now five operating x-ray lasers in the world, with a few more being proposed.

We have recently received the exciting news that, with support from the Knut and Alice Wallenberg foundation, Stockholm University, Uppsala University, Lund University, KTH and MaxIV Laboratory, we will be able to initiate a design study of an x-ray laser beamline (the technical term for such an instrument) in Sweden. The laser will be placed in Lund, within the MaxIV laboratory, exploit the existing, newly built linear accelerator that fuels the MaxIV synchrotron, and will operate in the so-called “soft” x-ray range, i.e. with a wavelength between 1 and 5 nm. This is the optimal “color” of x-rays if one wants to understand electronic and magnetic phenomena in solids, atomic physics, surface chemistry and biology.

The project covers 2 years of intense work aimed at designing the new beamline, estimate its construction cost, and test the properties of the electron beam at the linear accelerator at MaxIV towards x-ray lasing. We will also carefully design the setups where we will perform experiments, and how to combine those experiments with other lasers of longer wavelength: from the visible/UV, down to the infrared and the only recently accessible terahertz region.

We are very excited at the idea that we may be able to perform cutting-edge experiments here in Sweden, within a national community that is already prominent on the international stage, and that can now have the opportunity to contribute with an instrument of its own. The international x-ray community, which greatly contributed to the scientific case for this beamline, is as enthusiastic as us at this opportunity, and it eagerly awaits the next step.

With such an intense source of photons possibly becoming a reality, it is almost too easy to say that the future for science in Sweden looks extremely bright, and that we very much look forward to it.

– Stefano Bonetti, Condensed Matter and Quantum Optics Division
– Anders Nilsson, Chemical Physics Division

Read even: First step towards a Soft X-ray Laser at MAX IV Laboratory

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