Abstract

A precision collimated reference source (CRS) is manufactured by the Wyko Corp. This source has two functions: first, the CRS allows the user to verify the performance of the Wyko Ladite system, and second, it may serve as a characterized input to test the system response of an unknown system under test. Wavefront irregularity of the CRS unit is specified at <λ/100 rms over the central 6-mm clear aperture diameter. Collimation of the beam is specified at better than λ /15 peak to valley. Since residual aberrations present in the CRS are smaller than the aberrations inherent in the Wyko Ladite wavefront analysis system, testing a collimated reference source is not straightforward. Testing methods involve a geometric test to evaluate focus and several shear tests. Rotational shear is employed to evaluate nonrotationally symmetric aberrations, and lateral shear is used to evaluate rotationally symmetric aberrations. The shearing tests enable the inherent aberrations of the Ladite system to cancel out, revealing only the reference source aberrations. The geometric test, referred to as a paired-aperture test, supplies an excellent method for evaluation of the defocus of the unit. Further analysis is accomplished by comparing the wavefronts of several collimated reference sources that have been tested on the same Ladite system.

© 1989 Optical Society of America