Shadows are often an object of fascination. Whether when they protect us from the sun or because they are an insurmountable company whenever there is lighting. Shadows are also an object of study, and not only in the context of solar eclipses.
Light and shadow. The light has shadow. It may seem counterintuitive, but it is the strange conclusion reached by the team responsible for a recent experiment. The team responsible projected one laser beam onto another and observed the appearance of a shadow.
According to the team responsible for the experiment, the shadow cast by the laser beam is visible in plain sight, generating a contrast approximately equivalent to the shadow cast by a tree on a sunny day.
“Laser light casting a shadow is something that was previously believed to be impossible, since light generally passes through other light without interacting,” Raphael A. Abrahao, co-author of the work, explained in a press release. “Our demonstration of a very counterintuitive optical effect invites us to reconsider our notion of (what is) a shadow.”
The shadows. Shadows can become one of those concepts so omnipresent in our lives that we end up not paying much attention to them. At least from a scientific point of view or, at least, to satisfy our curiosity.
Shadows appear when an object interrupts the passage of light. But, whether due to the dual nature of photons or the fact that they have no mass, or because shadow is precisely the absence of light, thinking of light as an object that can give us shadow is difficult. This skepticism may be justified.
The experiment. For the experiment, the team shone a high-power, green laser through a ruby crystal cube. On the other side, the team illuminated the cuno with another laser, this one blue. The blue laser was then projected onto a screen where it was possible to see the shadow left by the passage of the green beam.
As the team explains, when crossing the ruby cube, “the green laser locally alters the material response to the blue wavelength. The green laser acts as an ordinary object and the blue laser acts as illumination.
The study has been published in an article in the journal Optics. This publication will allow other laboratories to try to replicate the experiment to determine if the results described correspond to reality.
What happens in the glass? Future experiments may also help us understand what exactly is happening at the subatomic level. According to the team’s interpretation, the effect “is a consequence of the non-linear optical absorption of the ruby.” This implies, they continue to explain, that the green beam increases the absorption capacity of the blue laser, which generates what can be perceived as a shadow.
For now, the team highlights that their experiment can help us better understand the interactions between light and matter. It could also be used in the future in the development of systems that improve our control of light beams in laser instruments.
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