The history of photomultiplier dates back to 1934 when it was first documented by RCA group based in Harrison, NJ. Harley Iams and Bernard Salzberg were the first to integrate a photoelectric-effect cathode and single secondary emission amplification stage in a single vacuum envelope and the first to characterize its performance as a photomultiplier with electron amplification gain. Photomultiplier tubes are extensively used as photodetectors in situations where high sensitivity is important. In addition to high sensitivity to a wide spectrum of light from UV to near IR they feature a low noise level, high frequency response and large collection area. These advantages have meant that despite all the advances in photodiode technology, photomultipliers are still used in virtually all cases when low levels of light need to be detected.