Hi. I'm curious about how a PSA (polariser-sample-analyser) ellipsometer works, especifically the detector bit. In an ellipsomenter, light passes through a polariser which puts it into a known polarisation state. After that it hits a sample (which may be an interface, a surface or a thin film) and because the Fresenel coefficients behave differently for different polarisation states, the components of the light interacting with the sample are modified differently, making the reflected light elliptically polarised. Light is then passed through an analyser and is collected by the detector. After the analyser, the electric field has an amplitude given by the sum of the components of the electric field before the analyser and is oscillating in the direction prescribdeb by the analyser. Now, my doubt is... what is the detector really measuring? Is it measuring the light intensity? How a single measurement can give any information about the sample? Thank you very much.