Normally, you think of things casting a shadow as being opaque. However, new research shows that under certain conditions, a laser beam can cast a shadow. This may sound like nothing more than a novelty, but it may have applications in using one laser beam to control another. If you want more details, you can read the actual paper online.
Typically, light passes through light without having an effect. But using a ruby crystal and specific laser wavelengths. In particular, a green laser has a non-linear response in the crystal that causes a shadow in a blue laser passing through the same crystal.
The green laser increases the crystal’s ability to absorb the blue laser beam. which creates a matching region in the blue beam that appears as a shadow.
If you read the article, there’s more to measuring shadows than you might think. We aren’t sure what we would do with this information, but if you figure it out, let us know.
Ruby has a long history with lasers, of course. That green laser pointer you have? It might not be all green, after all.
So it is a “NOT” gate… which, IMHO, is very interesting for photonic circuits.
So, in what way does this show that “light can cast a shadow”? As far as I can tell this shows that a laser alters a material, affecting its opacity. I don’t think this is any different in concept to transition lenses (aka photochromic lenses) which have been around since the 60s.
I’m sure there is a lot of actual innovative and useful research here, but the reporting (in phys.org and elsewhere) just seems… sensationalist
AFAIK, the photochromic lenses are based on a chemical effect, thus are much slower than this, which, if I get it right, is based on a quantum effect.
“Strictly speaking, it is not massless light that is creating the shadow, but it is the material counterpart of the polariton, which has mass, that is casting the shadow.” -Article. The author argues that a light wave in medium is fundamentally composed of both photons and excitations in the medium, which is why they are saying that the light creates the shadow. It is also a new effect unlike other light-induced changes in opacity.