Meters detect power parameter information about laser beams using liquid crystals to propagate the beam therethrough with photodiode detectors. The power parameters include intensity in watts per square meter, beam waist size, and the location of the focal spot based in light induced orientational phenomena...http://www.google.de/patents/US5621525?utm_source=gb-gplus-sharePatent US5621525 - Apparatus and method for measuring the power density of a laser beam with a liquid crystal
