OPTICAL BEAM SWITCHING DEVICES UTILIZING A PAIR OF PLANE MIRRORS

Where it is desired to "switch" a beam of radiant energy from a first to a second receiving element, it is proposed to introduce into the beam a pair of parallel facing plane mirrors rigidly attached to each other, along a line parallel to the reflective surfaces. This eliminates undesired change in the direction of the reflected beam caused by unintentional rotation of the two-mirror assembly about the line of introduction. The device may be used in a two-grating scanning monochromator to cause gradual change-over of the beam from one grating to the other. The two-mirror assembly movement is preferably interconnected to the grating drive to cause movement of the assembly at the appropriate time, and preferably in such manner as to allow reversing of the monochromator.