Lesson 4 – Beam Deviation + TIR

When light moves from one material through another material, it can exit at a different angle. This is known as beam deviation. This is common in optics like prisms, but it happens in common windows. Consider light moving from a material with a higher refractive index to a material with a lower refractive index. As the angle of incidence increases, there will be an angle that causes light to be refracted at 90° as it enters the second material, perfectly along the interface between the two materials. This special angle of incidence is known as the critical angle and the phenomenon is called total internal reflection (TIR) because no light is transmitted into the second material—it is all reflected at the interface. This is an essential phenomenon because it is responsible for the operational principle of optical fibers in the telecommunications industry, among many other applications.