Everyday observation suggests that light bouncing off a perfectly smooth mirror creates an accurate image without any alteration. However, this becomes less straightforward when the light itself has a more intricate structure—small distortions arise. Recently, these distortions were spotted for the first time in a lab setting by researchers from Tampere University. Their findings validate a fundamental optical principle that was anticipated over ten years ago. They also illustrate how this can be utilized, for instance, to analyze material characteristics.
Everyday observation suggests that light bouncing off a perfectly smooth mirror creates an accurate image without any alteration. However, this becomes less straightforward when the light itself has a more intricate structure—small distortions arise. Recently, these distortions were spotted for the first time in a lab setting by researchers from Tampere University. Their findings validate a fundamental optical principle that was anticipated over ten years ago. They also illustrate how this can be utilized, for instance, to analyze material characteristics.
Light behaves as a wave. Although scientists have recognized this basic fact for over a century, researchers in optics and photonics continuously uncover new properties and uses for light waves. At Tampere University, the Experimental Quantum Optics Group (EQO) delves into the intricacies of light’s shape—or its structure, as it is often described. The study of light’s structure has gained importance within modern optics, leading to advancements that span fundamental quantum physics, information science, and optical communication technologies.
In their latest research, the team demonstrated that the shape of a light beam undergoes a slight distortion when it reflects off a perfectly flat surface like a mirror. Although this distortion is minimal, it holds valuable information regarding the properties of the object, including its material composition. This phenomenon, known as the topological aberration effect, was predicted over a decade ago by researchers in the UK and has now been experimentally confirmed for the first time.
“While the notion of detecting a distortion may seem straightforward, we spent over a year fine-tuning our experiment and adapting the original theory to differentiate our findings from the various other natural beam deformations that occur in experimental research,” shares Associate Professor Robert Fickler, leader of the EQO team.
Whirlpools of light and darkness
Recent advancements in light wave shaping have led to a flourishing interest in structured light over the last few decades. Much of the excitement in this field is centered around twisted light waves, which not only travel at the speed of light but also spin during their journey.
“What’s intriguing about these twisted light fields is their presence of completely dark regions known as optical vortices, resembling whirlpools in water that lack water themselves. Our research has focused on observing how these vortices weave and shift when the light beam interacts with a flat surface, and what insights we can gain from these movements,” explains Academy Postdoctoral Researcher Rafael Barros, the lead author of the study.
The behavior of vortices in optical fields has long been a topic of investigation, often regarded as a complex mathematical challenge. In their research, the authors explored how the vortices in a twisted light field behave upon reflection from an object. They discovered that while each optical vortex moves in a complicated manner, their combined movement is influenced by the object’s qualities in a straightforward and predictable way. The researchers emphasize that their work could pave the way for innovative methods of assessing the properties of materials using structured waves, potentially introducing a new dimension to optical technologies.
