Innovative experiment takes “pictures” of light, blocks light, uses light to change the properties of matter

Light travels at a speed of about 300,000,000 meters per second as light particles, photons, or the equivalent of electromagnetic field waves. Experiments led by Hrvoje Petek, a professor of RK Mellon in the Department of Physics and Astronomy examined the ideas surrounding the origin of light, taking pictures of light, stopping light, and using it to change the properties of matter.

Petek worked with students and collaborators Prof. Chen-Bin (Robin) Huang of Tsing Hua National University in Taiwan and Atsushi Kubo of Tsukuba University of Japan in experiments. Their findings were reported in the paper, “Plasma Topological QuasiParticles on the nanometer and femtosecond scales”, which was published in the December 24, 2020 issue of Nature magazine.

Petek praised graduate student Yanan Dai for his foresight and work in this process.

“However, the denunciation of the research is that Yanan, who conducted the experiments and provided theoretical modeling, demonstrated that he was educated far beyond his Professor’s level and could persistently interpret nanofemto topological properties and optical field interactions,” he said.

The team conducted a rapid microscopy experiment, where they blocked green light pulses lasting 20 fs (2 × 10-14 s) as waves of light-electron density fluctuations, known as surface plasmon polaritons and propagation image of them on a silver surface at the speed of light. But they did this with a twist so that the light waves merged on both sides to form a light vortex, where light waves seemed to circulate around a common stationary nucleus like a whirlwind of waves. They can generate a film of how light waves are scratched at their nanometer (10-9 m) wavelength scale by imaging electrons that two photons of light coming together cause to emit from the surface.

The collection of all such electrons with an electron microscope forms images where light had passed, thus allowing researchers to take its picture. Of course, if nothing is faster than light, its picture cannot be taken, but by sending two light pulses with their advanced time division in steps 10-16 s, they can imagine how light waves combine causing their common amplitude to increase and fall at fixed points in space forming a slight vortex on the nano (10-9 m) -femto (10-15 s) scale.

Such light vortices are formed when you shine your red or green laser on a rough surface and see a point reflection, but they also have a cosmological significance. The vortex fields of light can potentially cause transitions in the order of the quantum mechanical phase to solid-state materials, such that the structure of the transformed material and its mirror image cannot overlap. In other words, the meaning of vortex rotation generates two materials that are topologically distinct.

Petek said such topological phase transitions are at the forefront of physics research because they are thought to be responsible for some aspect of the structure of the Universe.

“Even the forces of nature, including light, are thought to have emerged as symmetries that break the transitions of an initial field. “Thus, the ability to record optical fields and plasma vortices in the experiment paves the way for conducting ultra-fast microscopy studies of light-related transitions initiated in laboratory-grade condensed matter materials,” he said.

Reference: “Plasma topological quasi-fractions in nanometer and femtosecond scales” 24 December 2020, Nature.

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