What exactly is the detector of an ellipsometer measuring?

[Gabriel Maia]

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.

 

[Cutter Ketch]

Simply optical power. There are various choices as to how to measure optical power, but for a single beam system this can just be a photodiode. For imaging systems it can be a camera. All of the information is in the modulation of the intensity as a function of polarizer - analyzer orientation.

 

[Cutter Ketch]

Sorry for the double post. I didn't see the "single measurement" question. It isn't a single measurement. The polarizer or analyzer spins and the intensity is measured as a function of angle. In some systems a waveplate is spun. In some systems the variable waveplate is electro optical for fast measurement. In some systems a single orientation of analyzer and compensator are found that null the signal. While this is only one position it still takes multiple measurements to find it.

 

[Gabriel Maia]

Sorry for the double post. I didn't see the "single measurement" question. It isn't a single measurement. The polarizer or analyzer spins and the intensity is measured as a function of angle. In some systems a waveplate is spun. In some systems the variable waveplate is electro optical for fast measurement. In some systems a single orientation of analyzer and compensator are found that null the signal. While this is only one position it still takes multiple measurements to find it.

Thank you very much. The angle the intensity is a function of is the angle between polariser and analyser, right? Don't they do measurements based on the incidence angle on the sample as well?