Scientists at the SLAC National Accelerator Laboratory of the Department of Energy have created a novel technique to test the limits of the facility's Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL).
They developed a system that can generate X-ray pulses ten times more powerful than it ever was while remaining within the LCLS's current free-electron laser infrastructure.
(Photo : TOBIAS SCHWARZ/AFP via Getty Images)
A detail view is pictured inside of a so called experimenting hut (Experimentier-Huette) prior to the official inauguration ceremony of the XFEL international research facility in Schenefeld near Hamburg on September 1, 2017. The world's largest X-ray laser opens Friday September 1, 2017 in Germany, promising to shed new light onto very small things by allowing scientists to penetrate the inner workings of atoms, viruses and chemical reactions.
A detail view is pictured inside of a so called experimenting hut (Experimentier-Huette) prior to the official inauguration ceremony of the XFEL international research facility in Schenefeld near Hamburg on September 1, 2017. The world's largest X-ray laser opens Friday September 1, 2017 in Germany, promising to shed new light onto very small things by allowing scientists to penetrate the inner workings of atoms, viruses and chemical reactions.
Superpowerful Optical Laser Pulses
This novel system uses chirped pulse amplification (CPA), a method for creating modern, superpowerful optical laser pulses.
According to Haoyuan Li, University and the study's primary author, present X-ray laser pulses from free-electron lasers have a maximum output of about 100 gigawatts and typically have a complicated and chaotic structure.
"We've shown that we can achieve very impactful beam parameters of greater than 1 terawatt peak power and a pulse duration of about 1 femtosecond at the same time," Li said in a press release statement.
LCLS snaps pictures of the tiniest changes in molecules and materials, similar to an atomic-resolution camera.
But the timing of the laser pulses could become erratic with increased laser power, according to the team's report.
This inconsistency results from a distorted or misleading picture of what is occurring with the system, which scientists want to avoid. Current solutions for that issue drastically cut down on laser power, which restricts what researchers can achieve.
Due to these limitations, Diling Zhu, senior coauthor of the work, estimates that over 90% of XFEL laser studies conducted over the past ten years used the X-ray source as an ultrafast flashlight.
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How the CPA Works
CPA works by expanding the length of an energy pulse before it travels via an amplifier and a compressor that reverses the stretching made in the first stage. The outcome is a pulse that is extremely strong, clean, and brief.
CPA was created in the 1980s by physicists Donna Strickland and Gérard Mourou from the University of Rochester, who were awarded the 2018 Nobel Prize in Physics.
The creation of high-intensity pulses for optical lasers has been revolutionized by CPA, but Li said it has been challenging to adapt the method for X-ray wavelengths.
The researchers created a CPA method for producing high-intensity hard X-ray pulses within the beam characteristics of an existing free-electron laser by meticulous numerical modeling.
According to Li, the new system demonstrates that it is capable of creating terawatt, femtosecond hard X-ray pulses using current free-electron laser facilities, such as LCLS at SLAC.
The team's next step is building the system with a miniature prototype. Their findings were published in Physical Review Letters.
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