I loved doing stuff on the optical bench. It's amazing when you are so sure you are going to have one result, and it turns out, it's competely different!
Someone once said something similar to this: the greatest achievements in physics did not herald the word "Eureka!" but most likely the words, "Gee, that's funny........." (I think it was Feynman, but I can't remember, Samoth, help me out!)
Great page about interference
Interference Figures