Methods for Detecting Weak Light Signals

Theoretical and experimental evaluation of three low-level photodetection techniques, namely, lock-in, noise-voltage, and electron-pulse counting are presented. The 992 cm−1 Raman band of benzene excited by a 4.2-mW He–Ne laser operating at 6328 Å provided a weak light signal which was detected by an EMI 9558 A, cooled photomultiplier. The electron-pulse-counting method employing a pulse-height discriminator was found to be superior to the other methods with regard to both signal sensitivity and signal-to-noise ratio.