Light can spin like a wheel, not just a propeller
In short: We usually think of light as traveling in straight lines, but it can actually carry orbital angular momentum—a property that allows it to spin. While we have known about light's ability to rotate for decades, scientists are now discovering ways to make it spin sideways like a rolling tire.
For years, physicists understood that light could possess orbital angular momentum (OAM), which is associated with the tendency of a rotating object to keep spinning. This OAM manifests as swirls or vortices in the light's phase—the specific arrangement of peaks and troughs in electromagnetic waves. Early research focused on 'propeller-like' vortices, where the phase turns around the cross-section of a beam as it moves forward.
Recent breakthroughs led by Professor Howard Milchberg at the University of Maryland have revealed a different geometry: spatio-temporal optical vortices (STOVs). In contrast to typical propeller-style designs, these configurations transport transverse OAM; here, the phase rotates as a vehicle's wheel turns while moving with the beam. This discovery was initially met with skepticism by colleagues who found the idea of sideways-pointing momentum for photons to be 'weird' or incorrect.
The ability to manipulate these spirals has profound implications. Beyond fundamental physics, STOVs offer potential applications in optical communications, nonlinear optics, and exotic microscopy. Researchers are currently developing methods to change this transverse OAM as a light pulse travels, aiming to master the mechanics of how light can be twisted and steered in three dimensions.
In related fields, 'toroidal vortices'—ring-shaped structures with whirling disturbances—are already observed in nature, from dolphin-made bubble rings to meteorological microbursts. Scientists are now working to replicate these complex 3D shapes using photonic toroidal vortices, which can propagate without distortion in specific media by utilizing conformal mapping.
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Sources
- Summary by Intellect · source: How To Make a Spiral Out of Light—The Optical Vortex Experiment
- Also: New laser experiment spins light like a merry-go-round
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