What you propose is of course, not possible.
However, assuming you do have a one-way mirror that is 100% reflective on the inside, and at least partially transparent on the outside, you probably would not be able to store energy in it. You would not see it either, it would appear as an absence of light.
Such a device, if used in an area where any ambient light exists, would then proceed to absorb all of the photons which hit it. If the ball contained air, it would eventually become so ridiculously hot from all the heating of the air from the light that it would melt. If the ball contained a 100% vacuum (also not particularly possible). You COULD use it to store energy, but it would likely cause an incredibly large explosion once you broke it open, if you allowed it to collect light for any lengthy period of time. Assuming you built this in outer-space, which is not a 100% vacuum (although quite close), you would reach a critical point at which one of several things could occur.
1. Fusion of any particles that get trapped in the ball.
2. Anti matter is created.
3. The fabric of the universe within that ball is changed in some incomprehensible way, possibly resulting in a black hole or a worm hole.
The ball would likely melt before any of those things happened though.
Back to your original question, if the ball ONLY had a laser shone on it, it was 100% reflective no the inside and transparent on the outside, it would appear completely dark (although that wouldn't matter, because no other light would be going into it, so you wouldn't know the difference). You would simply see your laser beam stop where the ball was. If you shone the laser on it for too long, any of the aforementioned things would happen. In order for it to store energy, it would have to consist of a nearly total or total vacuum. When you broke it open, difuse laser radiation would shine in the direction of where the structure first failed (the beam structure would be eliminated by the curved surfaces it would be reflecting upon).
However, everything about this situation is pretty much impossible, because in order for it to be 100% reflective on the inside, it must also be 100% reflective on the outside.
Maybe i've been thinking too much too!
AAlasers