Twymann-Green Interferometer

A set up for the Twyman-Green interferometer is shown in (Fig.11.4.3(a)). The interferometer is used to test the flat surfaces, beam splitters, prism and lens. Light from a source S is collimated using lens L₁ which falls on a beam splitter and is divided into two beams which move towards mirrors M₁ & M₂ respectively. These beams are then reflected back and combine again at beam splitter. Another lens L₂ is used to project the fringe pattern on screen. The mirrors and beam splitters used in the set up are of high optical quality. Interference phenomenon takes place between two plane waves. A monochromatic source (such as laser light) or quasi monochromatic source (such as mercury vapour lamp along with different color filters to select desired ) is used to observe interference fringes. The straight line fringes are obtained when the plane waves enclose a small angle. The orientation of these fringes can be varied by changing the orientation of one mirror with respect to the other (finite fringe setting). The test surfaces/optical elements are introduced in the path of one beam. The various arrangements for different elements are shown in the (Fig.11.4.3(b))