Light is what we use to make photographs, but if your subject is light itself you might have trouble capturing it, as it's the fastest thing in the universe. A group of researchers has now found a way to create snapshots of light as it interacted with a metal surface.
As reported in Nature, a team of physicists from the University of Pittsburgh has created an approach to taking these snapshots, as well as stopping light in particular circumstances. Understanding these phenomena might have some importance in figuring out how the whole universe is organized.
The team performed an ultrafast microscopy experiment. They shone thousands of pulses of green light with a duration of 20 femtoseconds – 0.02 trillionths of a second – on a silver surface. The interaction between photons (the particles of light) and the electrons in the silver can be modeled like it was a single real particle. These “quasi-particles” are called plasmons or excitons and were key to this research.
The team shot the laser pulses from two different directions, and when they came together, the result was a plasmonic vortex. The two light waves appeared to be circulating around a stationary common point as a wave whirlwind.
The rises and falls of the light waves were tracked thanks to the electrons liberated from the silver surface, and the fact that the light pulses were happening every 0.1 femtoseconds. It is a bit like looking at something moving as it is illuminated by a strobe light. The approach gives the researchers a high-level of control over the quasi-particles created.
And this is where the study has some exciting and long-reaching potential. A tiny fraction of a second after the Big Bang, matter and light were muddled together in complex interactions. Light vortices are capable of creating structures that break symmetries. For example, they can generate solid materials whose mirror image cannot be superimposed onto the original.
These light vortices could have played a role at the very beginning of our universe, influencing the properties of our cosmos when it was incredibly dense and compressed. Phenomena like cosmic inflation that generate an exponential expansion of the Universe would blow up these differences, creating the differences we might be seeing in space today.
"Even the forces of nature including light, are thought to have emerged as symmetry-breaking transitions of a primordial field. Thus, the ability to record the optical fields and plasmonic vortices in the experiment opens the way to perform ultrafast microscopy studies of related light-initiated phase transitions in condensed matter materials at the laboratory scale," lead author Professor Hrvoje Petek said in a statement.