The setup involved a cube made of ruby, two laser beams, and a surface onto which the light was projected.
Shadows have long been a source of fascination. They provide us with protection from the Sun and are an ever-present companion whenever there’s light. Additionally, shadows are an object of study, extending beyond phenomena like solar eclipses.
Light and shadows. A research team at the University of Ottawa in Canada recently came to a surprising conclusion: Light itself can cast a shadow. In a groundbreaking experiment, researchers projected one laser beam onto another and observed the emergence of a shadow.
According to the scientific team, the shadow produced by the laser light is visible to the naked eye, creating a contrast similar to that of a shadow cast by a tree on a sunny day.
“Laser light casting a shadow was previously thought impossible since light usually passes through other light without interacting,” study co-author Raphael Abrahao said in a statement. He added, “Our demonstration of a very counter-intuitive optical effect invites us to reconsider our notion of shadow.”
Shadows. Shadows are a concept that’s so omnipresent in our lives that people often fail to pay much attention to them, at least not from a scientific perspective.
Shadows are created when an object obstructs the passage of light. However, due to the dual nature of photons, the fact that they have no mass, and because a shadow is essentially the absence of light, it can be challenging to think of light as an object that can cast a shadow.
The experiment. In the Canadian experiment, the research team projected a high-powered green laser through a cube made of ruby. On the opposite side, it illuminated the cube with a blue laser. The blue laser was then directed onto a screen, revealing the shadow produced by the passing green beam.
According to EurekAlert!, “When the green laser enters the ruby, it locally changes the material response to the blue wavelength. The green laser acts like an ordinary object while the blue laser acts like illumination.”
The team has published the study in the journal Optics. This publication will allow other laboratories to replicate the experiment to verify whether the results correspond to reality.
What occurs within the glass? Future experiments may also help better understand the subatomic processes at play. According to the Canadian team, “The laser shadow effect is a consequence of optical nonlinear absorption in the ruby.” Scientists explain that the green beam enhances the absorption capacity of the blue laser, creating what appears to be a shadow.
For now, the team emphasizes that their experiment enhances the scientific community’s understanding of the interactions between light and matter. It could also contribute to the future development of systems that improve the control over light beams in laser instruments.
Image | Raphael Abrahao et al.
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