With a 340W, 50x50mm TEC (thermoelectric cooler) arriving at work this week for a project we’re working on, Steve asked me to look at using Newton’s Rings to determine if this new TEC was flat enough to use as it was, or if we’d need to lap it with diamond lapping paste to improve the contact between it and the water cooled copper block it will be clamped to.
A large part of the problems I had when writing my dissertation for my degree came down the the flatness of the thermoelectric cooler (TEC) I was using and the clamping force I could achieve on it. Without both being as flat as possible, the thermal contact between the TEC and the heat sink was poor, and so the TEC didn’t heat or cool as well as when both were lapped flat.
Newton’s Rings provide a way to determine the flatness of two surfaces optically. With a piece of glass you know is flat, you can tell whether another surface is flat by looking at the interference patterns between the two surfaces. With a monochromatic light source and optical flat on order, Steve and I armed ourselves with our impatience, a telescope mirror blank (maybe almost flat), this excellent PDF and the TEC and copper block to see what we could see.