Scatter plate interferometry is a powerful method in testing mirrors, lenses and optical systems, particularly those with moderately long focal length. Actually, the size of optical systems under test is not restricted and the interpretation of the interferograms is almost intuitive.
In this research, the concave mirrors are tested by two interferometric systems; one with two identical scatter plates and the other with one scatter plate and one plane mirror. The first system can detect all the aberration information but is very sensitive to mechanical disturbance, such as vibration. The second system, insensitive to mechanical disturbance, can detect only the even-order aberrations, so that coma and tilt aberration will not be detected.
A zone plate can be used as scatter plate but it appears that the scatter plates made from photographic emulsion by recording speckle pattern are superior to zone plates.
Aberration characteristics of the rough surface concave mirror is assessed by coating transparent wax on the surface. The contrast of the fringes is not as high as that of polished mirrors but enough to accomplish the assessment of the aberration of the surface.
