Researchers have discovered that under specific conditions, a laser beam can cast a shadow, challenging traditional views on light and shadows. This finding could pave the way for new technologies where one laser beam controls another.
"Laser light casting a shadow was previously thought impossible since light usually passes through other light without interacting," stated Raphael A. Abrahao, the research team leader from Brookhaven National Laboratory. The study, published in Optica, details how researchers used a ruby crystal and certain laser wavelengths to demonstrate this effect through a nonlinear optical process.
The concept originated during a lunch conversation when some scientists questioned whether the depiction of a laser beam's shadow in 3D visualization software could be replicated in reality. "What started as a funny discussion over lunch led to a conversation on the physics of lasers and the nonlinear optical response of materials," said Abrahao.
In their experiment, researchers directed a high-power green laser through a ruby crystal cube and illuminated it with a blue laser from the side. The interaction between these two light sources resulted in a visible shadow where the green laser blocked the blue light. This phenomenon is due to optical nonlinear absorption, which increases the optical absorption of the blue illuminating laser beam.
"This discovery expands our understanding of light-matter interactions and opens up new possibilities for utilizing light in ways we hadn’t considered before," added Abrahao. The team measured the shadow's contrast based on the power of the laser beam, finding it comparable to that of natural shadows.
Future investigations will explore other materials and wavelengths to replicate similar effects.