| 摘要 |
<p>1405531 Optical apparatus SIEMENS AG 20 Feb 1973 [21 Feb 1972] 8206/73 Heading G2J A variable light-beam attenuator for use with a linearly polarized laser beam e.g. to form a stage or studio lighting source comprises a multi-layer polarization beam splitter mounted to rotate about an axis along which an incident laser beam can be directed, the layers being disposed at the Brewster angle relative to this axis. As shown, a pair of prisms 4, 6, each of which has a base angle of 45 degrees, have their base surfaces coated with alternate layers of zinc sulphide 12 and magnesium fluoride 13 and the two outermost layers are joined by a cement film 14. The entry and exit faces 3, 15 of the resultant beam splitter have reflection-reducing coatings while the third face of prism 4 is provided with an absorptive film 9. The beam splitter is mounted within support rings 10 and 11 for rotation about axis AA'. In use, a linearly polarized laser beam 1 is incident from direction A on the entry face 3 of prism 4 producing a refracted beam in direction A' e.g. for illuminating a stage or studio and reflected beams in direction A" which are absorbed at 9. As the beam splitter is rotated relative to a polariser (not shown) the intensity of the refracted beam varies between a maximum and a minimum.</p> |
