PROOF COPY 052211RSI A single photon detector for the measurement of optical activity in the deep sea

~Received 29 May 2002; accepted 15 August 2002!A module was constructed for the measurement of deep sea optical activity at a sensitivity level ofa single photoelectron. We describe the features of the module and a method for calibrating it. Theaverage sensitivity in the interval from 350 to 500 nm is 0.89 Hz/~photons cm