I didn't think so, but peep this.

And this, and this! My mind is not made up.

The only Google result for 'gravitational array reflection' is that Urban Dictionary page.

I think it's a bunch of baloney. The next time she uses the term, say "Oh, you mean a flashlight."

It certainly sounds like baloney, but I don't think this poor woman could tell a proton from a crouton, and I'd hate to call somebody's kid a liar.

The closest thing I can imagine to a photon cannon would be some kind of laser. You could potentially do someone damage by shining it in their eyes, or damage things in general by heating them up. Neither of those really sound like a 'cannon', though -- to me, a cannon works by physically pushing things around. It is possible to shift things using light, thanks to the radiation pressure, but it's a pretty darn small effect.

In fiction, Wikipedia tells me that Wing Commander had a photon cannon that was a special kind of laser cannon. And there's a photonic cannon in Star Trek lore.

The cool sci fi tanks from Bolo briefly had "laser cannons", and their infinite repeaters were briefly a kind of laser. These would probably be considered "photon cannons," I suppose.

If I was tasked with bringing a Photon Cannon to life just from the name I'd think of a repeating recoiless rifle that fired shells that are self contained chemical lasers.

Mitheral for the win.

I call mine a flashlight.