A type of shearing interferometry is presented in which the wave front under test interferes with a radially reversed replica of itself. The radial reversal of the wave front can be achieved either by an axicon—lens system or by use of a circular grating. Experimental verification is shown.
OLOF BRYNGDAHL, "Reversed-Radial-Shearing Interferometry," J. Opt. Soc. Am. 60, 915-917 (1970)