Implications of the Fresnel Equations:
As
Reflectance increases (until light is completely reflected)
When
such as when light propagates from glass into water
When
The implication here is that refraction increases as the angle of incidence increases. At high impinging angles, the wave cannot refract (theta-t) any more than 90°. Instead, it propagates along the surface (of the glass) and not into the medium below the glass.
What is important, however, is that total internal reflection generates an Energy field, or Evanescent Wave, that extends into the medium a very short distance. This field does not propagate like a light wave, but rather decays exponentially away from the interface of the glass/water (sample) interface.
The energy of the Evanescent Wave can (and does) excite fluorophores situated very close to the interface.
The penetration depth of the Evanescent Wave is a function of the intensity of the energy in Z.
Where
For example: with 500nm light, the depth of the Evanescent wave would be 100nm when light impinges on a glass/water interface.
