The Science Behind A "Project Bluebeam" Scenario

"3-D Mid-air Holography. Originally developed in Japan, this system utilizes an ionization effect that occurs when a beam of laser light is focused to a point in air. The laser beam itself is invisible to the human eye but, if the intensity of the laser pulse exceeds a threshold, the air breaks down into glowing plasma that emits visible light. The required intensity is achieved by very short, powerful laser pulses – each plasma pixel, or "flashpoint", lasts for only about a nanosecond, but the resulting image appears to last longer due to persistence of vision. As with film and television, the impression of a continuous image is maintained by refreshing the flashpoint pixels."
[link to my.opera.com]