Operating parameters for a multiple facet holographic disc scanner are adjusted on real time basis as a function of the actual diffraction efficiency of the facet region aligned with the impinging laser beam. The operating parameters are adjusted to achieve optimum signal levels independent of facet...http://www.google.de/patents/US4548463?utm_source=gb-gplus-sharePatent US4548463 - Holographic scanner control based on monitored diffraction efficiency
