CD: Cross Section During manufacturing, plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data.

CD Player

Reading a CD Al coating pit pit pit t Plastic substrate t = Pit depth = λ / 4 path difference = 2 t = λ / 2 Destructive interference at the pit edge. CD player can recognize the beginning and end of the pit. (1) (2) Reflected beam Incident laser beam (λ)

Iridescence in butterfly wings Each scale has multiple layers separated by air. Rather than having just the constructive interference from the top and bottom layer ,the many, equally spaced layers of butterfly wings create multiple instances of constructive interference. When light hits the different layers of the butterfly wing, it is reflected numerous times, and the combination of all these reflections causes the very intense colors in many species.

Anti-reflective and reflective coatings Anti-reflective coating: Reflective coating: For near normal incidence, destructive interference reduces the reflected light significantly if the coating thickness is about one-fourth of the wavelength of light and the index of refraction is intermediate between that of air and that of the surface. If the index of refraction of the coating is greater than that of the surface, then a quarter-wavelength thickness yields an increase in the intensity of reflected light.

Newton’s Rings t Light Source glass air

Michelson Interferometer

X-ray λ ~ 10 -10 m (~ 1Å ) Hot cathode filament Electron beam High voltage Tungsten target Anode Vacuum tube

Solid Crystals Atoms are aranged regularly in a lattice. Lattice spacing ~ 10 -10 m (~ 1Å ). Crystal lattice can act as a diffraction grating for x-ryas ( lattice spacing ~ wavelength).

X-ray diffraction

Crystalline planes d = a⅓ d = a

XRD from biomolecules Crystallized DNA (Rosalind Franklin, 1953) Crystallized enzyme