Reviewed by Danielle Ellis, B.Sc.Oct 3 2024
Researchers from Tampere University have observed small deformations in light reflection from complexly structured light fields, contradicting the expectation of an exact image provided by a perfectly flat mirror. This observation marks the first time such deformations have been seen in a laboratory setting and confirms a fundamental optical effect predicted over a decade ago. The journal Nature Communications published the study.
Illustration of the reflection of a twisted light field from an object, showing the topological aberration effect. Image Credit: Rafael Barros, Tampere University
Light is a wave. Although scientists have known this straightforward fact for more than a century, researchers in optics and photonics are constantly discovering and investigating new aspects of light waves.
The Experimental Quantum Optics Group (EQO) of Tampere University focuses on the subtleties of light's structure or shape as it is commonly known. With developments in quantum physics, information science, optical communications, and other fields, the structure of light has gained prominence in contemporary optics.
The researchers' most recent study has demonstrated that when light is reflected off of a mirror or other perfectly flat surface, it takes on a slightly distorted appearance. Despite the tiny deformation, it contains important details about the object itself, like the composition of its substance. For the first time, this so-called topological aberration effect has been observed. It was first theorized more than ten years ago by UK academics.
Although the general idea of observing a deformation seems rather simple, it took us more than a year to perfect our experiment and adjust the original theory to distinguish the effect from all the other beam deformations that are natural to experimental research.
Robert Fickler, Associate Professor and Group Leader, Experimental Quantum Optics Group, Tampere University
Whirlpools of Light and Darkness
In recent decades, the field of structured light has expanded rapidly due to technological advancements in light wave shaping. The phenomenon known as “twisted light waves,” which travel at the speed of light while also spinning, is largely responsible for the field's fascination.
What is curious in these twisted light fields is that they have points in them that are completely dark, optical vortices as we call them, like whirlpools in water that are themselves waterless. What we have done is to observe how these vortices thread and move around when the beam interacts with a flat object, and what we can learn from these movements.
Rafael Barros, Academy Postdoctoral Researcher and Study Lead Author, Tampere University
Research on the dynamics of vortices in optical fields has been ongoing for a long time, and it is typically thought of as a challenging mathematical issue. The authors' research has examined the motion of twisted light field vortices upon reflection from an object.
They have demonstrated that, despite the intricate movements of individual optical vortexes, the properties of the object govern the collective movement of these vortices straightforwardly and predictably.
The researchers note that their study will prompt novel approaches to quantifying the characteristics of materials with structured waves, giving optical technology a new dimension.
Journal Reference:
Barros, R. F., et al. (2024) Observation of the topological aberrations of twisted light. Nature Communications. doi.org/10.1038/s41467-024-52529-6.