Linear variable light attenuator

Claim 1

A variable attenuator for a laser light beam comprising, in combination: a. first and second optical wedges each having a pair of plane parallel surfaces and each comprised of an optically flat transparent plate with one surface coated with a layer of evaporated metal, the density of the layer varying as a function of the distance from one end of the plate, the rate of increase of the function representing the optical density of the first wedge, being equal to the rate of decrease of the function representing the optical density of the second wedge; b. mechanical means for holding the wedges in spaced relationship to each other and for moving the wedges simultaneously in opposite directions along a direction having a component in a plane normal to the laser light beam; and, c. means defining a light beam path through the wedges, the parallel surfaces of the first wedge being inclined at a small angle of the order of one degree to the parallel surfaces of the second wedge to divert from the light beam path unwanted multiple reflections of the light beam occuring in the space between the wedges, whereby coherent laser light may be continuously attenuated with the sum of the functions representing the optical densities being constant over the cross section of the light beam path through the wedges for all working positions of the wedges with respect to each other.