In diffraction-limited optical systems the number of optical components is rather high. Local changes in the refractive index of the order of 10−6 must be detected to guarantee an adequate performance of the system as a whole. Therefore, the Twyman-Perry method for the evaluation of refractive-index deviations from uniformity—further developed by Roberts and Langenbeck—has been programmed for a digital Twy-man-Green interferometer. If the glass block to be tested is slightly wedge shaped (wedge angle ~10−3 rad), the measurement can be carried out without coating the glass block. With the help of four interferograms the variations of the refractive index apart from a linear slope, as well as the thickness variations of the glass block, can be measured and displayed.
© 1985 Optical Society of America
Original Manuscript: April 16, 1985
Published: September 15, 1985
Johannes Schwider, R. Burow, K.-E. Elssner, R. Spolaczyk, and J. Grzanna, "Homogeneity testing by phase sampling interferometry," Appl. Opt. 24, 3059-3061 (1985)