Usually the scattered beam will be weak, in which case the (nearly) steady component of the detector output is a good measure of the instantaneous local oscillator intensity and therefore can be used to compensate for any fluctuations in the intensity of the laser.

A difference frequency only appears in the detector output current when both the LO and signal illuminate the detector at the same time, causing the square of their combined fields to have a cross term or "difference" frequency modulating the average rate at which free electrons are generated.

This can be improved a little by adding a load resistor to the detector output, but this also has the undesirable effect of decreasing sensitivity.

It gives better S/N ratio on the detector output.

Previously a chart recorder and more recently a data logger or personal computer records the detector output as a function of time so that each sample output appears as a peak whose height depends on the analyte level in the sample.

The state of the detector output is not directly affected by input voltage, but instead by the voltage drop across its input terminals (here, referred to as Va).

If the signal is different in frequency from the reference, the detector output will be periodic at the difference frequency.

Bias electrode(s) focus the resulting electrons toward the collector electrode, where they cause changes in the standing current which are quantified as the detector output.

This is because a narrower VBW will remove noise in the detector output.