Although the images, or holographs, projected appear to be three-dimensional, they have no substance. Thus they are undetectable by radar and can appear and disappear suddenly.
Known Uses of a Holographic Projector
Dr. Martin Davis used a Holographic Projector in his attempt to steal and sell the XJ-7 aircraft. Davis and his crew projected the image of a Mitsubishi Zero in order to force the XJ-7 and a military transport plane to change course. Davis also used the projector to create the illusion of his ghost. (SMDM: Nightmare in the Sky)
Other Laser Technology
Dr. Martin Davis is adept at the use of a Holographic Projector. It is unknown if he is the developer of the technology. Davis also employed laser technology in the development of a device that could disrupt engines and radio transmission. He called this device the Ignition Breaker.
OGA agent Clark Templeton O'Flaherty acquired laser beam secrets during a clandestine mission that he referenced (The Hornby Island Laser Incident). It is possible that Davis has illegally made use of that technology.