It becomes more and more of a problem the faster we have to make the measurement. If we have to make a new measurement every second, it's pretty easy. We're trying to make 3 billion measurements a second. That's pretty hard. That means we get three measurements every nanosecond.
Light goes about a foot in a nanosecond.
So, it's a difficult thing to do, to keep those measurement marks equally spaced. The UMaine effort was begun in 1990 by Irons and Hummels with support from the National Science Foundation and UMaine research funds. Irons began investigating the problem during a stint at Lincoln Labs at the Massachusetts Institute of Technology in 1985 and has since developed UMaine's ADC test facility into one of the few in the United States capable of this type of research. The puzzling thing is there aren't more universities working on the same problem. As a result, UMaine graduates have an advantage in this area.