Mid-infrared Mueller ellipsometer with pseudo-achromatic optical elements

Abstract

The purpose of this article is to present a new broadband Mueller ellipsometer designed to work in the midinfrared 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.

Effects of Polarizer–Analyzer Configurations for FTIR Spectroscopy: Implications for Multiple Polarization Algorithms

“…Indeed, there have recently been several studies that have demonstrated this potential. 11,12,25,28,29 Notably, Hinrichs et al, 11 recently showed the sensitivity of transmission cross-polarized FTIR to rapidly identify the anisotropy of polymer nanofibers. Given the previous discussion regarding the transmittance through crossed polarizers with respect to sample thickness, this approach appears to hold potential for analyzing the anisotropy of samples that are generally too thick for traditional FTIR methods.…”

“…Most p-FTIR studies utilizing polarizer–analyzer configurations are conducted with parallel-oriented polarizers. ,,,, However, the results presented in the previous section illustrate the potential of a cross-polarized FTIR approach for analyzing the anisotropy of organic materials, particularly the birefringent components, as one would expect, which are nearly unnoticeable in the parallel-oriented configurations. Indeed, there have recently been several studies that have demonstrated this potential. ,,,, Notably, Hinrichs et al, recently showed the sensitivity of transmission cross-polarized FTIR to rapidly identify the anisotropy of polymer nanofibers. Given the previous discussion regarding the transmittance through crossed polarizers with respect to sample thickness, this approach appears to hold potential for analyzing the anisotropy of samples that are generally too thick for traditional FTIR methods.…”

“…To address this gap within the literature, we present a theoretical and experimental approach to identify the effects of including an additional polarizer in p-FTIR analyses. It would be amiss to fail to mention that there is a faction of polarized IR techniques in which these factors are considered, those being IR ellipsometry and IR polarimetry. ,− While these techniques bear similarity to p-FTIR and offer the potential to derive identical variables, they typically diverge based on distinctive measurement geometries, polarization angles, or calculated variables. Hence, the findings presented here are focused on measurements conducted with p-FTIR in transmission (and, to an extent, transflection) utilizing multiple polarization angle methodologies to determine the direction and magnitude of orientation.…”