Detection of Weak Light Signals*

The experimental signal-to-noise ratios (S/N) of four photomultiplier light-detection systems are obtained for two values of the dc anode signal and dc anode dark current. The photodetection systems investigated are dc amplifier, lock-in, noise power, and combined lock-in plus noise power. Although there is no significant difference between the experimental S/N ratios of the noise power and lock-in-plus-noise-power system, they both produce significantly greater S/N ratios than the other methods. Theoretical S/N ratios are calculated assuming that shot noise only is present, and are compared with the corresponding experimental values.