Even if the beam is split, it's gravity locked in a certain direction by force, so only a fraction of its width would be redirected, and then that redirected energy would just continue to follow the gravitational path around the sword's blade. I personally assumed that the laserbeam could pierce those gems because 1) you stated that stray sparks punched holes in the barrier, 2) the disintegration ray is far more powerful than your average fire or lightning spell, the energies you mentioned, and it's especially effective at destroying physical constructs. 3) I don't think Corban could react fast enough to conjure that barriered graphene-aerogel in time; but when I find out if he can, I'll have the most accurate template possible to apply my own cast times in the future.