Abstract: Apparatus for circularizing an optical beam and directing the beam into an optical system has mutually perpendicular X, Y, and Z axes. The Z-axis is the propagation axis of the beam. A detector arrangement receives a sample of the optical beam. The detector arrangement has four detector elements arranged in four quadrants defined by an x-axis and a y-axis of the detector arrangement, perpendicular to each other. The x and y-axes of the quadrant detector are arranged at 45 degrees to the X and Y-axes of the apparatus. Signals from the four detector elements provide information on the extent to which the beam is not circular and on any displacement of the beam in the X and Y-axes.

Abstract: Apparatus for circularizing an optical beam and directing the beam into an optical system has mutually perpendicular X, Y, and Z axes. The Z-axis is the propagation axis of the beam. A detector arrangement receives a sample of the optical beam. The detector arrangement has four detector elements arranged in four quadrants defined by an x-axis and a y-axis of the detector arrangement, perpendicular to each other. The x and y-axes of the quadrant detector are arranged at 45 degrees to the X and Y-axes of the apparatus. Signals from the four detector elements provide information on the extent to which the beam is not circular and on any displacement of the beam in the X and Y-axes.