Schematic diagram of the beam path used in the Picometer Ellipsometer
 

The Picometer Ellipsometer uses the configuration P-BM-S-A (Polariser-Birefringence Modulator-Sample-Analyser). The output from the two signal channels are directly related to Re(r) and Im(r), where r is the fundamental quantity of ellipsometry, being the ratio of the amplitude reflectivities r = rp/rs. Traditionally this ratio is often written

r = tan expⁱ

so that
Re(r) = tan cos
Im(r) = tan sin

The parameter r is a much more direct representation of the ellipsometry signal than the ellipsometric angles and , which makes results more accessible to interpretation. However, since the Picometer measures both Re(r) and Im(r) simultaneously, the data can always be converted to the traditional notation using and .

Due to the modular design of the Picometer Ellipsometer, the default P-BM-S-A configuration can be easily configured for many other optical measurements such as measurements of reflectivity, transmission, birefringence, dichroism etc.