Ellipsometry compensator angle

Ellipsometry, Table 1 Zone relations for a PCSA null ellipsometer. P is the polarizer angle, C is the compensator angle, and A is the analyzer angle... 

In ellipsometry monochromatic light such as from a He-Ne laser, is passed through a polarizer, rotated by passing through a compensator before it impinges on the interface to be studied [142]. The reflected beam will be elliptically polarized and is measured by a polarization analyzer. In null ellipsometry, the polarizer, compensator, and analyzer are rotated to produce maximum extinction. The phase shift between the parallel and perpendicular components A and the ratio of the amplitudes of these components, tan are related to the polarizer and analyzer angles p and a, respectively. The changes in A and when a film is present can be related in an implicit form to the complex index of refraction and thickness of the film. 

In null ellipsometry information about the optical system is obtained from the azimuths of P, C, A, the relative phase retardation of the compensator 6q and, in the case of measurements on surfaces, the angle of incidence that reduces the dc or an ac-component of the detected radiation flux to zero. Photometric ellipsometry is based on measurement of the variation of the detected radiation flux as a function of one or more of the above parameters (azimuth angle, phase retardation, or angle of incidence). 

In 1960s, in order to reduce the time spending in angle calibration, H. Takasaki [11] used automation servomotor technology to drive polarizer and compensator and set the azimuth of polarizers automatically. However, in this configuration, it was still unavoidable to use human eye in the azimuth reading. Of course, the subsequent ellipsometry data processing was still involved in the human. So this type of ellipsometer was only a semi-automatic ellipsometer. 

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