Optics and Photonics Society of Iran

A phase wedge is formed by a transparent slab with non-parallel surfaces and a refractive index different from the refractive index of the surrounding medium. When a monochromatic light beam illuminates the phase wedge, due to the abrupt change in the phase of  the incident light, Fresnel diffraction becomes appreciable. The intensity of the diffraction fringes varies due to the change of the optical path difference (OPD) of the beam passing through the wedge. The OPD is happened due to the refractive index change along perpendicular to the edge and the change of the thickness along the edge of the wedge. The OPD dependents to the incident angle of the light,  refractive index of the wedge, refractive index of the surrounding medium, and angle of the wedge. Due to change of the thickness alonge the edge of the wedge, the diffraction fringes appears as periodic fringes with a specified pitch along the edge. In this paper, we consider the temperature related refractive index in optical glass. For this work, an optical wedge is heated from one end by a heater in vacuum. The temperature difference casues a refractive index change in the optical glass. So the OPD of the beam passing through the wedge is varied. As a result, the pitch of the periodic fringes varies. By measuring the pitch changing, we obtain the temperature related refractive index change in optical glass