A coherent laser beam is divided into an illumination beam and a reference beam. A portion of the illumination beam is passed through, or reflected off of, a subject to create a subject distribution, and a portion of the reference beam is passed through a reference object, or reflected off a reference...http://www.google.com.au/patents/US6802051?utm_source=gb-gplus-sharePatent US6802051 - Method and apparatus for reference distribution aerial image formation
