Laser beam casts visible shadow

Led by Jeff Lundeen, Associate Professor in the Department of Physics at uOttawa, in collaboration with the Boyd Research Group, this discovery marks the first time such an effect has been observed and challenges understanding of how light interacts with itself.

Typically, photons pass through each other without interacting, but the Ottawa experiment revealed an effect in which the shadow of a laser beam shows the same behaviour of shadows cast by solid objects.

"We've shown that under certain conditions, light can actually block other light, creating a shadow," Professor Lundeen said in a statement. "This opens up exciting new possibilities for controlling and manipulating light in ways we never thought possible before."

The team's experimental setup involved shining a green laser beam through a ruby crystal while illuminating it from the side with blue light. This arrangement created a shadow on a surface, visible to the naked eye. The effect occurs due to reverse saturation of absorption in the ruby crystal, which allows the green laser to block the passage of blue light, resulting in a dark region that follows the contours of the laser beam.