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Effect of retro-reflector diameter on testing optical systems

In the use of ball bearings as retro-reflectors for testing optical systems in a double pass configurations, care must be taken when choosing the radius of the ball bearing. Using too small a radius can adversely effect the wavefront error as presented by the interferometer. The wavefront error, being a function of wavelength, can be significantly altered due to this ball bearing error, particularly in long wavelength IR systems tested with a visible light interferometer. This paper is the result of research towards understanding and modeling this error in the presence of spherical aberration.