There is an interesting article here http://focus.aps.org/story/v18/st4 about a method for tunnelling light through usually opaque materials. Half way through they mention that one light ray becomes two: "When a light ray passing from glass into air strikes the interface at a sufficiently shallow angle, it reflects entirely back into the glass with no transmission into the air. In this effect, known as total internal reflection, some of the electromagnetic field strays across the boundary between the two materials as a so-called evanescent wave, which carries no energy away. But if the evanescent wave encounters another block of glass a short distance away, a true light wave with reduced intensity appears in the second block." I am interested to know where the extra energy for the second light wave comes from, and is this a good way of building a power station, cycling the energy through the system and getting apparently more out each time.