Say I'm doing the double-slit experiment with photons as the particle and want to add a detector just behind each slit to eliminate the interference pattern. Where would I get a detector like that?
They're based on photomultiplier tubes. An example is referred to in this lab assignment.
Photon Detector: The detectors used in this experiment are two Hamamatsu R1527 photomultiplier tubes (PMTs)