Strehi Ratio For Square Segments Of A Parabolic Mirror.

The need for increasingly larger diameter mirrors is met by using segments to build up a large mirror surface. The segmentation of the mirror surface results in the deterioration of its optical properties, most notably those caused by the diffraction effects. The presence of the segments also introduces the additional complexity in the mirror assembly and alignment procedure. A precise segment alignment is based on the optimization of the Strehl ratio for the segment using a laser beam. An expression for the Strehl ratio for an off-axis square parabolic segment is obtained. It is shown that a segmented mirror is most effectively utilized in an optical system with a large F-number.