Abstract
Dual channel multiplex spectroscopy systems have recently been found to be convenient devices for precise calibration of Raman spectrometers and for comparing spectral lines of almost identical wavelengths. The essential feature of such systems is as follows: Each light source is chopped with a different phase (or with a different frequency), and both signals are amplified by a single photomultiplier and amplifier. They are then separated by a pair of time or frequency gate amplifiers (box car integrators or lock-in amplifiers) which also convert them from ac to dc. Finally, they are fed into a two-pen recorder. This type of system has a practical disadvantage for people who prefer to use photon counting detection systems. Photon counting appears to be more popular than lock-in amplifiers and box car integrators for the detection of low intensity spectra as in Raman spectroscopy. For weak light signals it gives a better signal-to-noise ratio than any other system.
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