Clocking Ultra-fast Electron Bunches

Jul 30, 2010 by Kendra Snyder
(top) Schematic layout of the electro-optical arrangement. (bottom) The electro-optical module with a YAG crystal for electron beam position monitor.

( -- Brookhaven researchers have developed a device that acts like a high-tech stopwatch for speedy packs of electrons just trillionths of a second long. This new diagnostic tool could aid in the development of x-ray free electron lasers (FEL), sources that produce pulses of light up to one billion times brighter and 1,000 times shorter than those produced at conventional storage ring light sources.

Like a high-speed strobe light, the ultra-short bursts of light produced from an FEL allow scientists to take stop-motion pictures of chemical reactions, biological processes, and various other atomic-scale events. FELs create this valuable x-ray light by shooting a series of ultra-short bunches of electrons through an array of specialized magnets. The shorter the electron bunches, the more powerful the resulting light.

"In recent years, the bunch lengths of electrons in accelerators have decreased dramatically, producing extremely bright pulses of light that are on the same time scale as vibrations in molecules and the creation or breakage ," said NSLS researcher Xi Yang. "But in order to synchronize the time-dependent process being studied with the x-ray pulse, we need a new set of beam diagnostics."

So how do scientists measure the length of these picosecond-scale pulses? It's not easy. There have been previous successful attempts, but only with limited resolution and complicated steps.

At the NSLS Source Development Laboratory (SDL), Brookhaven researchers have demonstrated a high-resolution measurement system that's nondestructive to the electron beam and can be easily transported among facilities.

In the setup (first proposed by Brookhaven researchers in 2002), a beam of electron bunches is sent across the top edge of a thin, "electro-optical" crystal. Traveling at close to the speed of , each electron bunch emits an electric field that travels downward through the crystal. At the same time, a single, line-focused laser pulse is sent straight through the broad side of the crystal, where sections of the laser line are encoded with spatial information from the electron bunches. A special camera at the end of the device collects this data.

"Using this monitor, we are able to take robust measurements of the electron bunch length," Yang said. "The tolerance on timing jitters can be many picoseconds."

The results were published in the December 7, 2009 edition of Applied Physics Letters.

Now, the goal is to measure electron pulses an order of magnitude smaller, in femtosecond duration, or quadrillionth of a second range. The Brookhaven researchers hope to accomplish this resolution enhancement by using a thinner crystal, which will minimize the smearing of the while the laser probe travels through the crystal, giving the encoded spatial information less time to "degrade." This detailed picture will let scientists analyze fine structures within the pulses, such as micro-bunching - the arrangement of electrons within a larger bunch.

Explore further: Team invents microscopic sonic screwdriver

More information: X. Yang, T. Tsang, T. Rao, J.B. Murphy, Y. Shen, X.J. Wang, "Electron Bunch Length Monitors Using Spatially Encoded Electro-Optical Technique in an Orthogonal Configuration,"Appl. Phys. Lett., 95, 231106 (2009).

Related Stories

Tapering a Free-Electron Laser to Extract More Juice

Nov 20, 2009

( -- Researchers from the NSLS and Science Applications International Corporation (SAIC) have demonstrated a technique that could be used to significantly improve the quantity and quality of light ...

A Bunch of Electron Chicanery

Nov 21, 2006

As the Linac Coherent Light Source (LCLS) takes shape over the next few years, one of the key issues occupying the minds of physicists is controlling the size and shape of the electron pulses used to generate ...

Have Gun, Will Travel (at Light Speed)

Jan 25, 2007

The front third of the linac is undergoing an extreme makeover, metamorphosing into a first-of-its-kind hard x-ray free-electron laser, the Linac Coherent Light Source (LCLS). But even with the engineering ...

Recommended for you

Researchers prove magnetism can control heat, sound

May 28, 2015

Phonons—the elemental particles that transmit both heat and sound—have magnetic properties, according to a landmark study supported by Ohio Supercomputer Center (OSC) services and recently published by ...

How researchers listen for gravitational waves

May 28, 2015

A century ago, Albert Einstein postulated the existence of gravitational waves in his General Theory of Relativity. But until now, these distortions of space-time have remained stubbornly hidden from direct ...

What's fair?: New theory on income inequality

May 27, 2015

The increasing inequality in income and wealth in recent years, together with excessive pay packages of CEOs in the U.S. and abroad, is of growing concern, especially to policy makers. Income inequality was ...

Scientists one step closer to mimicking gamma-ray bursts

May 27, 2015

Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such ...

User comments : 0

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.