SLAC scientists create twisted light

September 19, 2013 by Lori Ann White, SLAC National Accelerator Laboratory

These images shows the spiral structure of the coherent OAM light emitted from a beam of electrons accelerated to nearly the speed of light and arranged into a helix by a simple laser. Left: An intensity map. Note the dark center where the light cancels itself out, resulting in a cross section resembling a doughnut. Right: A phase structure map, clearly showing the helix described by the light. Credit: Hemsing, et al.
( —Scientists at SLAC have found a new method to create coherent beams of twisted light – light that spirals around a central axis as it travels. It has the potential to generate twisted light in shorter pulses, higher intensities and a much wider range of wavelengths, including X-rays, than is currently possible.

First described two decades ago, twisted is attracting attention from researchers in fields as diverse as telecommunications, quantum computing, condensed matter research and astronomy because of one unique property: It possesses (OAM). Twisted light has already been used by astronomers to find , and researchers have demonstrated that it can transmit more information through than the current industry standard.

Until now, researchers created twisted light by shooting through masks or holographic gratings. But a team of from SLAC and UCLA has shown they can create it with a beam of electrons, in much the same way SLAC's Linac Coherent Light Source (LCLS) X-ray laser uses electrons to generate pulses of X-ray laser light.

There are several advantages to generating corkscrew light beams this way, said SLAC Erik Hemsing, who is lead author of a paper in the September issue of Nature Physics. Free-electron lasers can generate light in a vast range of wavelengths and in extremely short, bright pulses, opening up the possibility of generating OAM light at the X-ray wavelengths of, for example, LCLS.

"There are lots of other ways to make OAM light," said Hemsing, "but most don't translate to X-rays."

The experiments were carried out at the Next Linear Collider Test Accelerator (NLCTA), SLAC's small test accelerator. Although the OAM light the team coaxed out of their was in the , Hemsing said there's no reason the same technique can't be used to create OAM light of much shorter wavelengths, and thus much higher energies – X-ray energies.

Erik Hemsing is one of a team of young accelerator physicists putting electrons through their paces at the Next Linear Collider Test Accelerator. Credit: Brad Plummer/SLAC

The experiment is only one of several being conducted at NLCTA to create "beams by design," or light with specific properties, by controlling the electrons that generate it, said Tor Raubenheimer, a professor of particle physics and astrophysics at SLAC and Stanford, who works closely with the NLCTA researchers.

"Erik is one of the young star physicists down at the NLCTA," he said, "and has been part of a very productive physics program that is supported by both the Department of Energy Offices of Basic Energy Science and High Energy Physics."

The research is a continuation of work done in photon science facilities, from synchrotron light sources like SLAC's Stanford Synchrotron Radiation Lightsource to free-electron lasers like the LCLS, where scientists have learned how to control and shape the electron bunches used to generate light. At the most advanced facilities, such as the LCLS, bunches of accelerated electrons are sent through undulators – exquisitely tuned series of magnets that force the electrons to wiggle back and forth in such a way they generate laser light.

In the case of corkscrewing light, researchers send two pulses – one containing electrons, the other laser light – through an undulator simultaneously.

Creating twisted light at the NLCTA, SLAC's test accelerator. Credit: Greg Stewart/SLAC

The combination of laser pulse and undulator imprints an energy pattern on the electrons. As they pass through another grouping of magnets called a chicane, the electrons reposition themselves like race cars on a curve, and hit the next straightaway arranged in the shape of a corkscrew. This "helically microbunched" arrangement of electrons then enters a second undulator that causes them to wiggle and emit spiraling light.

Intense beams of spiraling X-ray light could open the door to new condensed matter research, said Hemsing. But there is one challenge to overcome: As with the development of the first X-ray lasers, technology is ahead of demand. Researchers who could take advantage of the special properties of OAM light don't necessarily know it's available or what it could do for them.

But the success of LCLS should make things easier, showing the potential for working with new forms of light. "People can see how well the LCLS works," said Hemsing. "Now they're interested in what other kinds of light we can make."

Explore further: New tool to measure X-ray pulses borrows from SLAC history (w/ Video)

Related Stories

New test bed probes the origin of pulses at LCLS

July 24, 2013

It all comes down to one tiny spot on a diamond-cut, highly pure copper plate. That's where every X-ray laser pulse at SLAC's Linac Coherent Light Source gets its start. That tiny spot must be close to perfect or it can impair ...

First atomic X-ray laser created

January 25, 2012

Scientists working at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have created the shortest, purest X-ray laser pulses ever achieved, fulfilling a 45-year-old prediction and opening the door ...

Mastering microbunching for linac-based light sources

August 22, 2013

( —Designing accelerators requires years of research and development. Throughout the Lab's history, scientists and engineers at Brookhaven have helped lead the way in designing accelerator technologies for cutting-edge ...

Small X-band photoinjector packs powerful punch

September 25, 2012

(—Accelerator physicists at SLAC have started commissioning the world's most compact photoinjector – a device that spits out electrons when hit by light. Photoinjectors are used to generate electrons for free-electron ...

X-ray laser pulses in two colors

March 27, 2013

( —SLAC researchers have demonstrated for the first time how to produce pairs of X-ray laser pulses in slightly different wavelengths, or colors, with finely adjustable intervals between them – a feat that will ...

Recommended for you

CMS gets first result using largest-ever LHC data sample

February 15, 2019

Just under three months after the final proton–proton collisions from the Large Hadron Collider (LHC)'s second run (Run 2), the CMS collaboration has submitted its first paper based on the full LHC dataset collected in ...

Gravitational waves will settle cosmic conundrum

February 14, 2019

Measurements of gravitational waves from approximately 50 binary neutron stars over the next decade will definitively resolve an intense debate about how quickly our universe is expanding, according to findings from an international ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (10) Sep 20, 2013
It is certainly refreshing to hear of good mission oriented research from high energy physicists who don't have their brains turned into spaghetti searching after imaginary extra dimensional strings or loops.
Sep 20, 2013
This comment has been removed by a moderator.
1 / 5 (3) Sep 23, 2013
Science needs to progress to next dimensional nature of reality Index
2.6 / 5 (5) Sep 23, 2013
This thread crackpot index: 3/5

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.