A 300 MHz Optical Discriminator-Counter

The prediction of future CO2 content in the atmosphere is not completely credible because the oceanographers and terrestrial ecologists do not agree on the global CO2 balance. Very precise measurements of O2/N2 ratio using Raman scattering over a few years' period could provide important information and lead to the explanation of the disparity in the atmospheric CO2 balance. An optical discriminator-counter has been developed to count closely spaced optical events in the few photon level. Simulated optical events as close as 2.5 ns apart had been positively detected by using selected photomultipliers and optimized discriminators. Testing of the optical discriminator-counter was done by using an electrical pulse pair spaced 3 ns apart and also by a similar optical pulse pair generated by fast light-emitting diode. The photomultiplier is capable of counting an average single photoelectron pulse frequency of 50 MHz and has a sensitive detecting area of 50 mm in diameter. The discriminator performance will be discussed.