Applications of Diffraction, Interference, and Coherence

"Take the first letters of all the words (except *by* and "of") and write them in order. You get the word **laser** ... which is the name of the device that produces such a beam of light." "An interesting thing happens if you pass light through a large number of evenly-spaced parallel slits. Such an arrangement of slits is called a **diffraction grating**. An interference pattern is created that is very similar to the one formed by double-slit diffraction." "Thus, the condition necessary to obtain constructive interference for a diffraction grating is $d \sin\theta = m\lambda$, for $m = 0, 1, -1, 2, -2, \ldots$ ... Note that this is exactly the same equation as for two slits separated by *d*." "The **Rayleigh criterion** for the diffraction limit to resolution states that two images are just resolvable when the center of the diffraction pattern of one is directly over the first minimum of the diffraction pattern of the other. ... two point objects are just resolvable if they are separated by the angle $\theta = 1.22 \frac{\lambda}{D}$." "Tiny, fingerlike structures in regular patterns act as reflection gratings, producing constructive interference that gives the feathers colors not solely due to their pigmentation. The effect is called **iridescence**."