Probably the coolest thing that I did in 2005.
I needed to measure the thickess of a film of an amino acid that I was growing in a vacuum chamber. The sublimation oven was made from a stout 5 Ohm alu'-clad resistor and a block of carefully filed (and shiny) copper. I could get the amino acid to sublimate (we even sublimated intact C60 buckyballs!), but had no way to measure the condensed layer thickness.
So, I spies an old laser pointer, I does, and has me an idea.
A quick RS order later (for some nice big photodiodes), I had a dual-beam interferometer that gave about 20nm precision for the film thickness. Calibration against an AFM led to an accuracy of about 10% or so, and some further ideas about the utility of optical interferometry in the home.
Okay, in my home.