This 2" diameter collimation tester is a wedged window that allows for quick testing of collimation by utilizing shearing interferometry. When the collimation tester is aligned at a 45 degree angle of incidence with respect to the incident beam, two wavefronts are formed - one from the front surface of the wedge and one from the back surface. Where these two wavefronts overlap, the user will see interference fringes. When the fringe pattern is horizontal, the collimation of the input beam is considered to be well collimated. This optical element is also a good teaching tool for shearing interferometry. See Application Note #25 - Collamation Tester for shearing interferometry theory and an outline of the method of test.
