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.