Watching an explosion in super slow motion is what we expect from just about any Hollywood action blockbuster.
But capturing details of an explosion that’s about the same size as a protein? That might not have the same appeal as a Michael Bay movie, but don’t let that fool you. There’s a lot we can learn from the sizzle of a nano-sized bang.
Nanoplasma is exactly what it sounds like – bursts of charged particles contained on a sub-microscopic scale as a nanoparticle disintegrates. Now, for the first time, researchers have used a cutting-edge X-ray laser to watch one in high detail.
X-rays are incredibly useful for studying the world of insanely tiny things. Their tight wavelengths act like thin, sensitive fingers capable of feeling every nook and cranny of objects too small to study with your typical microscope.
Unfortunately, what they promise in detail they lack in subtlety. Hitting a delicate object such as a protein with an X-ray and studying the aftermath is like blindly caressing a snowflake to determine its shape. It can be hard to tell what is authentic and what’s clumsy prodding.
Learning exactly what the brutal stabbing of X-rays does to a crowd of atoms would at least help researchers interpret their results, sifting out the details that are significant from the ones that show blast damage.
We recently reported on US researchers using bursts of light from an X-ray free-electron laser called the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory to study the ionisation of water.
A pulse of intensely focussed electromagnetic radiation in the X-ray region heated water molecules to a temperature hotter than Earth’s core in 75 femtoseconds, blasting the molecules apart into a soup of charged particles they could examine.
This time, another team of physicists used the Spring-8 Angstrom Compact free electron Laser (SACLA) in Japan to strip apart a few thousand atoms of xenon.
Similar to the LCLS, the SACLA focusses a beam of X-rays onto an area that’s a fraction of the width of a human hair, shining with the brightness of thousands of Suns.
As you might imagine, being hit with such an intense pulse – even if it is for less than 10 quadrillionths of a second – will do more than tickle.
The researchers filled a vacuum chamber with about 5,000 xenon particles and hit them with a pulse of X-rays that lasted less than 10 femtoseconds, causing them to lose electrons and leave behind a variety of positively charged ions.
The aftermath wasn’t up for debate. What they wanted to know was exactly how the atoms lost their electrons. Did they all shake free at once? Was it a progressive reaction?
Hollywood cinematography would use high-speed cameras to capture every glorious detail of an explosion. But femtosecond photography requires some clever thinking.
The team used a bright flash of near infra-red laser light, which was absorbed by particles making up the nanoplasma.
The absorption pattern revealed key details about the variety of positive xenon atoms, from those that had lost just a handful of electrons to some that were stripped of as many as nearly half of their stash.
By repeating the experiment with different intervals between the blast and the ‘photo finish’ infra-red snap-shot, the researchers could shoot a virtual slow-motion scene of xenon nanoplasma formation.
Those details pointed to a specific process of ionisation that was more like a steady electron version of pass-the-parcel than a sudden, chaotic free-for-all of electron flight.
Breaking it down, atoms of xenon transform into a bubble of nanoplasma in stages.
Energy absorption was followed by a small number of xenon atoms shedding electrons. These created zones of positives and negatives that continue to hold the plasma together.
Understanding brief moments of a tiny, contained explosion holds the key to understanding how atoms are arranged when the heat is on.
Applied to more complex systems, it could lead to models that better describe the shapes and arrangements of nanomaterials.
Or, throw in a lens flare or two, and we can one day look forward to a more organic version of Transformers on the small screen.
This research was published in Physical Review X.