Modern nulling ellipsometers use computers to rotate the elements and to automatically calculate the ellipsometry signal very quickly. However, the nulling technique is not ideal for automated instruments because it is based on measuring a zero signal. This was an advantage in the early ellipsometers because the human eye is very sensitivy to small changes in the signal around the 'null'. However, modern light detectors exhibit significantly higher noise at low intensities. A technique that is more suited to modern-day instrumentation is Phase Modulated Ellipsometry, where the polarisation of the light is modulated at a high light throughput.
Phase modulated ellipsometry is described in more detail on the next page.
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