Abstract: In an optical system with an optical axis in which an image is to be focused at an image plane, an improved chopper which can be driven at a high rate for obtaining dither about the focal point in the system includes first and second chopper blades, each having at least one notch in their periphery, the chopper blades mounted to a common shaft adapted for rotation, parallel to each other and essentially perpendicular to the optical axis and on opposite side of the image plane, the outputs of one of the blades will representing an ahead of focus edge response and the other of said blades a behind focus edge response which can be sensed and processed to carry out correction of the optical system.

Abstract: A passive compensating device which compensates for angular and translational misalignment errors in a polarized beam and assures the projected beam centroid remains at the same position. The device splits the incoming beam into two beams. Thereafter, optical orienting means disposed to intercept the two beams is operative to rotate the wavefront of both beams so that the composite beam exiting a combiner has two components wherein one component has its wavefront rotated 180.degree. about two orthogonal axes with respect to the other beam. Accordingly, the composite beam centroid is maintained at one position regardless of jitter of the beam entering the compensator device.

Abstract: A circuit for selecting a clipping level including a passive clipping element having a transfer function like that of either a zener diode, two series connected opposing zener diodes or other passive clipping elements. An inverting operational amplifier with a selectable gain couples to the passive clipping element and by adjusting the amplifier gain, the clipping level can be selectively reduced to almost zero from that of the clipping level for the passive clipping element itself.

Abstract: A coeloscope beam expansion and direction system for high energy lasers wein the system utilizes a cassegrain telescope folded into a coelostat. The beam expander optics are placed between the azimuth axis gimbal and the elevation axis gimbal rather than at the output of the optical train as in the telescope concept or at the input of the optical train as in the coelostat concept.