Physics · Ch 6 — Optics
Prisms Making Use of Total Internal Reflection
Prisms Making Use of Total Internal Reflection
Right-angle glass prisms can be used instead of silvered mirrors to reflect light through or through a full , or to invert an image without changing its size, purely by relying on total internal reflection at the glass-air interface -- provided the material's own critical angle is less than (true for both ordinary crown glass and flint glass, whose critical angles are well under ). Because these TIR prisms need no silvered coating at all, and lose no light to absorption by a metallic coating the way an ordinary mirror does, they ar …
What this figure shows. Three right-angle prism configurations. In the first, a ray entering perpendicular to one face strikes the hypotenuse face at 45 degrees (above the roughly 41.8-degree critical angle of ordinary glass) and totally internally reflects, turning the beam through 90 degrees. In the second, two successive 45-degree internal reflections turn the beam through a full 180 degrees, sending it back parallel to but offset from its original direction. In the third, a similarly arranged pair of internal reflections is shown flipping (inverting) an image without altering its size -- all three effects rely purely on total internal reflectio …