Relativistic electrons have been used to carry out “ghost imaging” of a sample for the first time. The research was done by Siqi Li at SLAC National Accelerator Laboratory and colleagues, who used a clever way of getting around the problem of producing two correlated electron beams. The technique could be used to improve analysis techniques that use beams of electrons to probe the properties of materials.
Optical ghost imaging is a useful tool that can spatially resolve the characteristics of a sample using just a single-pixel detector – rather than the multipixel arrays found in digital cameras. The technique involves splitting a beam of light into a pair of correlated beams called the signal and reference beams. The signal beam strikes the sample before hitting the single-pixel detector. The reference beam goes directly to a conventional, multipixel detector. By measuring the correlation between the intensities of the beams as they hit their respective detectors, an image of the sample can be reconstructed using data from the multipixel detector, without directly imaging the sample itself.
Recent studies have explored how ghost imaging could also be done using X-rays or even beams of atoms, with applications ranging from medical imaging to tests of quantum mechanics. Now, Li and colleagues have turned to relativistic electrons with energies greater than about 10 keV. These are used in a range of experimental techniques to characterize various properties of materials.
Low radiation doses
Their motivation is that ghost imaging could reduce both image acquisition times and sample radiation doses for these techniques. The team also argues that ghost imaging could be useful for experiments for which there are no easily-implementable spatially resolved detectors – including electron spectroscopy and time-resolved electron scattering.
The big challenge, however, is coming-up with a way of splitting a beam of relativistic electrons to create two beams suitable for ghost imaging.
Li and colleagues avoided this problem by using a laser to modulate the output of the photocathode that they used as their source of electrons for the signal beam. Knowing how the signal beam is modulated provides the required information that would normally be obtained from the reference beam.
X-rays yield ghost images
The team tested their ghost imager by firing the signal beam at metal ring sample. By correlating the intensity of the electron beam picked up by a single-pixel detector with the laser beam, the physicists could reconstruct an image of the ring in a multipixel light detector. Furthermore, the twin benefits of a short image acquisition time and little radiation damage in the sample were also achieved.
The team now hopes to extend their techniques to other beam types including relativistic ions, plasmas, and neutrons.
The research is described in Physical Review Letters.
