Lesson Plan

Explain what coherent light is and how stimulated emission produces a laser beam

Describe how laser properties (directional, intense, narrow) enable specific industrial and medical applications

Explain how a diffraction grating works, why it produces a sharper pattern than a double slit, and how it produces iridescence in everyday objects

Calculate grating spacing or diffraction angle using d sinθ = mλ, and find a wavelength in a medium using λₙ = λ/n

Describe how gratings are used in monochromators, spectroscopes, and DIC microscopy

State the Rayleigh criterion and calculate the resolution limit θ = 1.22λ/D for a circular aperture or lens

17.2

"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."