I explained this already. It's in my post above:
Originally posted by Darth L. Dipsit
A better way to think of this is matter converted to energy. This can only be achieved by spending energy. When matter is accelerated to the speed c, 1 x 10^8 m/s, it becomes energy. However, it is very hard to make a compact particle accelerator. That is the problem. [B]Stopping the beam can be achieved by ionizing the gas used to make the laser (assuming you're using a noble gas). Now, since the ionization energy is so high because the valence shell of every single noble gas is full, that's hard to do. But it's possible. The application of this is that when two noble gases are released, with ions of opposite charge released with them, the repulsion generated between the ions, which, due to their attraction with the noble gas laser, must stay in a straight path, COULD be used, hypothetically, to cause the beam to stop, or to cause to lasers to repel one another. This would effectively allow one to have a lightsaber. That would be the process. However, I have never heard of a compact particle accelerator, so the concept is harder to manifest.[/B]