Tolerancing and alignment of a three-mirror off-axis telescope - art. no. 667601

When the optical elements of a system are not collinear, there are advantages to aligning all elements simultaneously. This paper presents the steps taken to prepare for system alignment and the alignment plan for such a system. A tolerance analysis of the system defines the compensators necessary for system alignment and allows an estimate of the expected magnitude of initial aberrations present in the system. Polarization and pupil aberrations are characterized in order to further understand expected system aberrations before alignment. A two step alignment plan is outlined. First, a CCD array placed at the focal plane indicates spot size and shape as elements are aligned. Once spot size is minimized, the CCD array is replaced by a ball bearing for retroreflection. Useful interferograms can be obtained with which remaining aberrations can be minimized. This technique is presented as the alignment plan for an off-axis telescope system consisting of one spherical and two ellipsoidal mirrors.