For interferometric testing of polished surfaces and wavefronts with the best physically accessible accuracy it is good to use a perfect wavefront reference originating from light diffraction by a pinhole aperture in a point-diffraction interferometer (PDI).
It is evident that phase shifting (PS) interferometric measurements with the use of the PDI should be fulfilled adequately to perfectness of its wavefront reference unless high accuracy expectations will not be met. High accuracy of the reference beam phase shifting of the two-beam PDI is produced by a two staged alignment procedure being performed on-line when PS fringe patterns (frames) are being saved.
This procedure is a time frequency filtering of intensity function of each pixel performed in order to extract regular sinusoids from a set of erroneous and noisy signals. The results of wavefront retrieval from the saved set of PS frames using any N bucket algorithm by the Durango software in both cases – not aligned and aligned – are compared.
This research helps keep the PDI accuracy corresponding to perfectness of the wavefront diffraction reference. Also this research may help in PS measurements performed by other types of interferometers where phase shifts are realized by test part movement.
Date Published: 18 December 2012
PDF: 8 pages
Proc. SPIE 8550, Optical Systems Design 2012, 85500R (18 December 2012); doi: 10.1117/12.980910