Optical tunneling is demonstrated by frustrated total internal reflection.
- A green laser diode (from a laser pointer) falls on a glass prism. The angle of incidence is greater than a critical angle, resulting in light being totally internal reflection.
- There is evanescent light leaking from the prism. But this light is difficult to tap off, unless a second prism is placed really close to the first one.
the second prism is almost conjoined with the first prism using an index matching fluid (Cargille’s BK 7 Matching Liquid). - The fluid is able to mate the prisms really well, yet it keeps a small gap between the prisms. Light can tunnel across this classically forbidden region and transmit into the second prism. Total internal reflection has been frustrated.
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- Light is totally internally reflected from a prism
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- A prism placed close by does not frustrate the total internal reflection
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- A second prism almost adhering to the first prism picks off the evanescent wave
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- Light is totally internally reflected as it traverses a thin slab of glass
