FEATURE SCIENTIFIC LASERS
‘It’s virtually impossible to get beam time [at x-ray free electron laser facilities]’
g
light, and then send the resulting electron bunch through what is called an ‘undulator’ or ‘wiggler’ (a structure of alternating opposing magnets). Forcing the electron bunch to proceed in a wavy motion, they emit X-rays forward at the maxima and minima of the wave motion. The result is an extremely bright X-ray laser, many orders of magnitude brighter than HHG sources so that researchers can not only probe electron motion but potentially control it. Already, isolated GW-scale soft X-ray attosecond pulses have been generated at X-FEL facilities.
Democratising attosecond science Even though huge advances have been made and important insights into fundamental physical processes unlocked, a central problem that has haunted attosecond science since the beginning has been accessibility. The complex, expensive laser set-ups required to conduct attosecond science have remained in the hands of a select few for two decades now. However, the situation is changing:
“People in attosecond science will remain those pushing the frontiers of laser technology,” says Vampa. “But I think attosecond science is becoming progressively more democratised, thanks to better laser sources that are easier to operate and with improved capabilities.” “When I was a PhD student, I spent 90 per cent of my time aligning the laser and only 10 per cent was spent actually collecting data,” recalls Chini. “These were all homebuilt lasers that were very, very complicated, and were difficult to use.” Fast-forward to today and Chini, Vampa and anyone else working in the field can order high-quality complex ultrafast optical components and femtosecond laser sources from the likes of Edmund Optics, Coherent, Amplitude, Trumpf, Thorlabs and more, simplifying experimental setups and meaning attosecond experiments can be conducted with a push of a button. “Having this advantage of a laser that
just works allows people who are not laser experts to be able to access these very short timescales,” Chini says. “I think that as the field advances, the big discoveries are going to be made by collaborations with chemists, biologists and solid-state physicists, and so being able to transition attosecond science from something that
22 Electro Optics November 2022
exists only in a few labs worldwide to something that’s more widely available motivates me.” To this end, recently Chini’s team
developed a technique that allows industrial-grade lasers – costing around $100,000, far less expensive than current bespoke set-ups – to perform HHG and generate attosecond pulses. Soon after, a separate team using a similar technique achieved the first demonstration of an industrial-grade laser actually generating and characterising attosecond pulses. Elsewhere, Vladislav Yakovlev (Max Planck Institute of Quantum Optics, Germany) and his colleagues are developing new, simpler and less expensive techniques for attosecond measurements: “Our labs are focused on investigating, inventing, developing different approaches for attosecond-scale experiments that do not require big expensive vacuum chambers, that do not rely on attosecond light pulses but instead rely on very fast, very nonlinear gating mechanisms,” he says. “We call this attosecond spectroscopy 2.0.”
Going brighter Efforts such as these are undoubtedly slowly democratising attosecond science performed using HHG, but those interested in multiphoton and nonlinear X-ray physics, or researchers aiming to control electron motion, require brighter sources. And their research remains severely hampered by the paucity of X-FEL facilities. Only five X-FELs exist worldwide: the
European XFEL in Hamburg, Germany; the Linac Coherent Light Source (LCLS) at Stanford University, USA; the SwissFEL in Switzerland; the Spring-8 Angstrom Compact Free Electron Laser (SACLA)
Tau Systems’ CEO Bjorn Manuel Hegelich and COO Jerome Paye
in Japan, and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL- XFEL) in Korea. “It’s virtually impossible to get beam time on them,” says Bjorn Manuel Hegelich, a professor at the University of Texas at Austin, USA. “If you’re a company, forget it. You will not get to use it.” Hegelich is founder and CEO of Tau
Systems, a start-up with ambitions to make X-FELs significantly cheaper and more compact. “We’re replacing the conventional radio frequency copper structure accelerator with a laser-driven accelerator,” he explains. By commercially introducing this technique for laser-driven particle acceleration, the idea is for electrons to surf on three-dimensional plasma waves, thereby accelerating them to ultra-high energies over a short distance. “The accelerator at Stanford is many kilometres long and the one at Hamburg as well; these are big campus-size machines. We get the same electron energy over a distance of about 10 centimetres.” Simulations reveal that Tau Systems’
X-FELs will be capable of producing pulses in the range of 100 attoseconds. With the first machines touted to be available from around 2026, the team believes that attosecond x-ray science will be within the grasp of not only the wider scientific community but also, finally, industry. “This is where you can really do single- particle imaging of molecules of proteins to understand these chemical and biological processes on a very fundamental level,” says Hegelich. “And if you do that, you can then start thinking about designing drugs, for example, from the molecular level upwards, basically like Lego building blocks.” EO
@electrooptics |
www.electrooptics.com
Tau Systems
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58
