Five ways to put tiny targets in front of an X-ray laser

February 3, 2015, SLAC National Accelerator Laboratory

X-ray devices have long been used to see the inner structure of things, from bone breaks in the human body to the contents of luggage at airport security checkpoints. But to see life's chemistry and exotic materials at the scale of individual atoms, you need a far more powerful X-ray device.

Enter the Linac Coherent Light Source (LCLS) X-ray laser at the Department of Energy's SLAC National Accelerator Laboratory. This mile-long machine, a DOE Office of Science User Facility that opened in 2009, merges decades of particle accelerator know-how with cutting-edge X-ray and laser technology.

Its unique X-ray laser pulses, a billion times brighter than any previous X-ray source on the planet, are the  "ammo" in a high-tech shooting gallery with tiny samples as targets. With each direct X-ray hit comes an opportunity to unlock secrets hidden in the molecular structure of the sample.

But it's a whole lot harder than scoring bull's-eyes on ducks at a carnival booth. At LCLS, the X-ray ammo is traveling at the speed of light, can be focused to a spot more than a million times smaller than a bullet, and the targets can be more than 10,000 times smaller than the typical shooting-gallery duck.

Pulses last just quadrillionths of seconds, about the time it takes light to travel the breadth of a human hair. They're fired 120 times per second, and in many cases have to hit tiny samples that are tumbling randomly so you can't tell which way they're facing when they're hit. Each pulse can damage or destroy its target, so there are no second chances.

Raising the stakes even higher, your targets may have taken a lot of time, effort and money to produce, you may need millions of direct hits to get conclusive results for your experiment and you have only a limited time to do that. Missed shots can be the difference between discovery and disappointment.

To maximize the odds of success, SLAC researchers adapt techniques from other applications and invent new ways to precisely align, time and refresh samples, whether , gas or solid, so they reliably connect with laser pulses. Here's a look at five important techniques:

1. Drop-on-Demand Systems

Like a dripping water faucet but with more complex physics behind it, a "drop on demand" system provides a precisely measured and timed supply of tiny liquid droplets containing whole or dissolved samples.

Some of these systems in development borrow from inkjet printer technology developed in the 1970s. They can use "piezoelectric" crystals (see above), which change shape in response to electric current to precisely push out streams or droplets of liquid, or they can do this with acoustic waves or other applied pressure.

2. Simple Liquid Jets

Jets are like mini squirt guns streaming samples of liquid or gel into the X-ray pulses. They're often used to study delicate, nanoscale samples such as crystallized proteins, which offer an ideal X-ray window into a protein's atomic structure.

The jet's nozzle can be shaped to produce a stream of the desired thickness – for instance, to accommodate crystals of a certain size. If the nozzle is too narrow, the samples can quickly clog it. And if the stream is too thick, the liquid solution can interfere with the quality of the crystal images.

The simplest type of liquid jet, called a Rayleigh jet (see above), produces a stream as wide as its nozzle, and can also produce a flow of droplets for experiments.

3. Virtual Nozzle Jets

A more complex jet, popular in LCLS experiments involving crystals, uses a flow of gas around the nozzle to further squeeze and narrow the liquid or gel stream. This design, called a "gas dynamic virtual nozzle" or "flow focusing" jet (see above), can create unbroken streams of liquid just millionths of an inch wide.

4. Aerosol Jets

If you want to reduce the amount of liquid surrounding samples – as you might when studying living viruses, cells or cell components – you can spray them from an aerosol jet, which produces a fine mist like the one from a perfume bottle. These aerosols may be propelled by gases or produced by electric currents that break sample-containing liquid into sprays of tiny droplets.

Another sophisticated tool that's been customized for LCLS is the aerodynamic lens system (see above). It uses streams of gas and a series of gun-like chambers to produce very narrow streams of liquid and a more regular spacing of samples. This allows researchers to deliberately hit and study individual particles.

5. Translation Stages

Researchers can study the properties of materials, such as the strength of exotic metals exposed to extreme temperatures and pressures, with motorized platforms called translation stages (see above) that rapidly move samples in a gridded pattern to continually expose fresh sections to the X-ray .

While this method was in use prior to LCLS, it had to be customized to match the high repetition rate of LCLS pulses.

Explore further: Robotics meet X-ray lasers in cutting-edge biology studies

Related Stories

Robotics meet X-ray lasers in cutting-edge biology studies

November 24, 2014

Scientists at the Department of Energy's SLAC National Accelerator Laboratory are combining the speed and precision of robots with one of the brightest X-ray lasers on the planet for pioneering studies of proteins important ...

New tool puts LCLS X-ray crystallography on a diet

October 30, 2012

A tiny device invented at SLAC National Accelerator Laboratory will make it much easier for scientists to determine the structures of important, delicate proteins by greatly reducing the amount of protein needed for study.

Scientists map protein in living bacterial cells

September 4, 2014

( —Scientists have for the first time mapped the atomic structure of a protein within a living cell. The technique, which peered into cells with an X-ray laser, could allow scientists to explore some components ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...


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.