What would science fiction be without laser beams? From handheld ray guns to spaceship-mounted turbolasers, the futuristic weapon of choice definitely involves bright, colorful blasts of energy. In the early 21st century, projectiles still remain the standard means of inflicting damage from a distance. Yet continued research into "directed-energy" weapons by the United States military, among others, could someday bring lasers to a battlefield near you. Lasers are already used in guidance, targeting and communication applications, but significant technological obstacles stand in front of turning them into weapons by themselves. For certain niche scenarios, lasers might prove themselves ideal. It...