Wired takes a look at the psuedoscience of Halo weaponry and gadgetry, including the Spartan Laser and the Bubble Shield:

Some of the equipment came about through happy accident. One of the most popular new tools -- the "bubble shield," a pocket of temporary protection from weapons -- nearly didn't make it into the game. Bungie's designers had been bandying it about as a concept, but didn't fully commit to developing it for the game until it was featured in a TV advertisement last December. The ad showed the Master Chief throwing down a bubble shield -- with its distinctive, honeycombed shape -- to survive a missile attack.

Almost sounds as if the existence of the advertisement itself swayed Bungie into actually developing the bubble shield as a deployable!