During recent decades, many applications of optical surface have been found. Aspheric surfaces are specifically considered because of their ability to focus light without aberration. Accuracy and image quality of these surfaces encourage us to find a simple way of testing the non-spherical surface . Interferometry is an appropriate method to find out the aberration of surfaces in a fraction of wavelength range. The most important part of this method is analysis of the fringes pattern. Since the interferogram analysis of non-null tests is not favorable, one need to design procedure of high precision null tests .
We used a Fizeau interferometer set up with a spherical reference wave front and found circular fringes with missing information near the edge . Then a grating that looks like real fringes pattern, was designed and placed over light path to achieve the smooth and parallel moiré fringes [4,5]. Finally we applied Phase – Shifting Method to interpret the aberration .
During this method the grating had been the major error reference that cost λ∕20 deviation or less. So, as a conclusion, one could achieve high accuracy and a low-cost way of testing surface by used of Moiré technique on interferometer set up.
© 2011 Optical Society of AmericaPDF Article