A multiple beam or "multiphoton" absorption effect is used for creating three-dimensioal sensible objects including optical elements and three-dimensional computer-type data storage and retrieval systems. The objects and systems are made according to the invention by at least two beams of optical electromagnetic...http://www.google.com.tw/patents/US4288861?utm_source=gb-gplus-share專利 US4288861 - Three-dimensional systems
