Total Internal Reflection

1. Total Internal Reflection

2. Total Internal Reflection • When light passes from one material into a second material where the index of refraction is less, the light bends away from the normal. At a particular incident angle, the angle of refraction would be 90 degrees and the refracted ray would skim along the surface. At angles of incidence greater than the critical angle the light would be totally internally reflected.

3. Critical Angle • Sin (critical angle) = n(2)/n(1) • For angles less than the critical angle, the light would be refracted. • For the critical angle, the light would skim along the boundary. • For angles greater than the critical angle, the light would be totally internally reflected.

4. Example • For the air-water interface determine the critical angle • Sin(critical angle) = n(2)/n(1) = 1.0/1.33 = 0.75 • Sin 49 degrees = 0.75 • The critical angle for the air-water interface is 49 degrees.

5. Example • For the air-glass interface determine the critical angle • Sin(critical angle) = n(2)/n(1) = 1/1.50 = .67 • Arcsin (0.67) = 42 degrees • At angles less than 42 degrees light will be refracted. At 42 degrees light will skim along the boundary. At angles greater than 42 degrees light will be totally internally reflected.

6. Fiber optics • Glass and plastic fibers • Extremely narrow fibers can be used • Light can be transmitted along it with almost no loss because of total internal reflection

7. Applications of fiber optics • 1. telecommunications (verizonFios) • Telephone calls, video signals, computer broadband • 2. Medicine • Fiber optics used to transmit clear picture • Examples: bronchoscope, colonoscopes, endoscopes