  The purpose of this article is to present a new broadband Mueller
ellipsometer designed to work in the mid-infrared range, from 3 to 14 microns.
The Mueller ellipsometer, which can be mounted in reflection or in transmission
configuration, consists of a polarization state generator (PSG), a sample
holder, and a polarization state analyzer (PSA). The PSG consists in one linear
polarizer and a retarder sequentially rotated to generate a set of four optimal
polarization states. The retarder consists in a bi-prism made of two identical
Fresnel rhombs disposed symmetrically and joined by optical contact, giving the
ensemble a "V" shape. Retardation is induced by the four total internal
reflections that the beam undergoes when it propagates through the bi-prism.
Total internal reflection allows to generate a quasi-achromatic retardation.
The PSA is identical to the PSG, but with its optical elements mounted in
reverse order. After a measurement run, the instrument yields a set of sixteen
independent values, which is the minimum amount of data required to calculate
the Mueller matrix of the sample. The design of the Mueller ellipsometer is
based on the optimization of an objective criterion that allows minimizing the
propagation of errors from raw data to the Mueller matrix of the sample. The
pseudo-achromatic optical elements ensure a homogeneous quality of the
measurements for all wavelengths. The performance of the Mueller ellipsometer
in terms of precision, and accuracy, is discussed and illustrated with a few
examples.
