An X-Ray Laser’s New Corrective “Eyeglasses”

A new type of lens improves the focusing precision at the world’s most powerful X-ray light sources.

Eyeglasses
Using a method called ptychography, the team of researchers measured errors in X-ray beams at synchrotrons and a free-electron laser. The information allowed them to manufacture customized corrective glasses for an individual beam. Left: Desired shape and depth of a corrective plate based on ptychography data. Right: A corrective plate carved in quartz. Image courtesy of SLAC National Accelerator Laboratory

The Science

X-ray free-electron lasers, such as the Linac Coherent Light Source (LCLS), have had a significant impact on many scientific disciplines. LCLS produces brilliant and short pulses of X-rays for researchers to view the details of samples with unprecedented temporal and spatial resolutions. The challenge for the instrument scientists at the LCLS is how to focus the X-ray beam on the sample without distorting the beam’s quality? X-ray lenses require precision manufacturing. Instead of attempting a “LASIK surgery” on the lenses at the beamline, researchers found a way to put X-ray “eyeglasses” on the X-ray beam.

The Impact

The team’s “eyeglasses” provide a path to aberration-free X-ray optics to obtain detailed images of matter. Better optics will harness the full potential of current and future light sources. This approach also opens up new opportunities in fields as diverse as high-resolution imaging and plasma physics. These opportunities could lead to the materials needed for more powerful computers, damage-resistant aircrafts, and cleaner sources of energy.

Summary

Various optical elements are routinely used in modern synchrotron sources and X-ray free-electron lasers to confine the X-ray beam and focus it onto the sample under investigation. These elements include multilayer mirrors and compound refractive lenses. The fabrication of these X-ray optical elements requires high precision using the most advanced fabrication technologies, such as lithographic nanofabrication and thin film deposition. Any imperfection in the optical elements due to the fabrication process or to the limitations of available technologies results in a non-ideal (that is, aberrated) focused beam. At the Matter in Extreme Conditions endstation at LCLS, researchers have found a new way to correct for the imperfections introduced by a series of compound refractive lenses in the focused beam. The scientists used two techniques to characterize the aberrations for the entire unit. Then, they used a short pulse laser ablation technique to make a phase plate that corrects for aberrations (just like making eyeglasses for a patient but the patient in this case is the X-ray beamline).

Source : U.S. Department of Energy