The fruitfly of ultrafast X-ray science is breathing just fine at FemtoMAX

The FemtoMAX beamline team has successfully conducted their first time-resolved experiment with the MAX IV linac operating in 10 Hz mode.

On the Thursday evening of December 3rd, the FemtoMAX beamline recorded their first ultrafast time-resolved scan with the MAX IV LINAC operating in 10 Hz mode. This is a tremendous milestone and when we call up Jörgen Larsson it feels like we are interviewing someone who just crossed an Olympic finish line. The comparison is not far off as the team has been working hard towards this moment even a slight bit longer than your average Olympic team, since 2015.

“You ask how I feel? I think you can hear it in my voice,” says Jörgen Larsson, the beamline manager of FemtoMAX. “It’s relief and joy as the experiment setup works so well! We’ve been working so hard, and I really want to take this moment and highlight the collaboration across MAX IV that made this possible and especially the present and former members of our team here at FemtoMAX. For example, the so-called post-sorting system we realised for the time recording is an important development in its own right and will most probably attract a lot of interest. Also, the sample environment and the data analysis are essential components of the experiment.”

Enough intensity for speed
Firing an electron pulse through the linear accelerator ten times per second means that the FemtoMAX beamline sitting at its end receives enough X-ray intensity for ultrafast experiments to be possible. It will take a couple of days more to evaluate the time resolution achievable at FemtoMAX but it is at least been confirmed to be better than 500 fs when we’re writing this. Ultrafast X-ray science is important because a lot of the building blocks and processes in nature are rapid. In a simplified analogue, one could say that trying to take a picture of a process with a too slow shutter speed will get us a blurry image.

“Two of the things that our users will be working with using this new setup is phase transitions and electron excitations in materials,” explains Larsson. During a phase transition, the atoms move a couple of Ångström and they move approximately with the speed of sound. If you make the calculation you will see that the time scale is on the hundreds of femtoseconds. For electronic excitations, the timescale is around the same. The applications we see of the experiments are for example artificial photosynthesis, fast storage media that lets you read as fast as you write, as well as energy storage.”

Using the right fruitfly
The sample used to confirm the time resolution in the first experiment was a bismuth crystal. Using laser a laser pulse, the crystal can be excited to start vibrating or breathing as it’s called. The breathing mode can then be measured using X-rays. The breathing will move the atoms in its lattice in a way so that it becomes more symmetric. This resets the rules for which reflections can be seen in diffraction. The quick extinguishing of the diffraction spot can be used to probe the time resolution. This sample is likened to another often used model organism in science.

“The bismuth crystal is called the fruit fly of ultrafast X-ray science,” says Larsson with a laugh.

The next step now is to get everything ready for the users.

“We are working hard to be able to offer these possibilities to users in the upcoming call and it’s looking really promising going forward, concludes Larsson.


Learn more about the FemtoMAX beamline

Front page photo: Hanson Lu, Unsplash