A wave plate or retarder is an optical devicethat alters the polarization state of a light beam traveling through it. In thepresent setup, the diode laser light passes through polarizer to producelinearly polarized light. It then passes through the half wave plate L/2. TheL/2 plate produces linear polarised light. For different angles of the L/2plate with respect to optic axis only the polarisation plane changes. The maximumand minimum are not changed which can be investigated with the analyser overthe range -90 to +90 degrees.