Diffraction in lasers

I met an amazingly smart 2nd year grad student on my geology trip. A bit of background - two dozen geologists (actually, two astro kids and a Mech E were included in the jovial bunch) traipsed their way down to Baja California -- not in such a lackadaisical manner, with more intent -- but we made our way down to explore a bunch of rock formations, paleomag, a bit of cretaceous-dinosaur-fauna things, etc.

A few of us had wandered down to the beach at the Salton Sea the first night. When lasers came out, there was a period of comparing the power output of the lights and the distance this corresponded too.

But when you put a slight obstruction in the beam of the light -- we were using green lasers, best for seeing in the dark and for pointing out stars -- you get a diffraction pattern in the output light. There is a very obvious pattern of dark and light. Now, apparently, these are the Fourier transform of a single slit diffraction pattern! The light is blocked for exactly a top-hat function, and the resultant pattern has an intensity (not energy) that we see. The transform of the energy is the sinc function, but the intensity of the light is the sinc function squared.

Now, imagine two obstructions -- two hairs. On the ground, then, you see the pattern repeated, the standard diffraction of light and dark that progressively gets dimmer farther from the center. This is the first and the second fourier transform.

Yay :) You can do this for any number of obstructions!

Reflecting the laser off your teeth, your are confronted with a large number of organic shapes that have an apparent depth to the layers. They form moving shapes that crawl in green shadows across the ground, changing and disappearing. These are the fourier transform of...saliva. Ha ;)