A highly sensitive optical detector for use in deep underwater

We have developed an optical detector module for use in deep underwater experiments that will search for high-energy neutrinos from cosmic rays and astronomical sources. This module is sensitive to single photons, is operable under high pressure, functions automatically and is remotely controlled. The optical module is based on a 15 in. diameter photomultiplier tube (PMT), with control and read-out electronics mounted inside a 17 in. diameter glass pressure housing. The photomultiplier output signal is converted into two optical pulses by the electronics, one giving the hit time and time-over-threshold of the PMT output pulse and the other giving the charge-integrated PMT signal. Information on the arrival time and intensity of light can be extracted from these pulses. The time jitter of the optical modules is ∼6 and ∼2 ns at FWHM for one photoelectron and ∼100 photoelectrons, respectively. The unit requires 10 W power delivered at 48 V DC on a line with superposed bidirectional control signals. Fast output is uni-directional on a multi-mode fiber optic link to a remote time digitizer. The module has been successfully tested and calibrated in the laboratory, and several have briefly operated in the deep ocean.