Ellipsometry with an undetermined polarization state

TL;DR

This paper introduces a method for polarization measurements that does not require knowing the absolute polarization state, enabling accurate ellipsometry even with unknown or randomly varying polarization conditions.

Contribution

It demonstrates that generalized polarization states, preserved through birefringent media, can replace absolute polarization states for precise ellipsometric measurements.

Findings

Achieves ellipsometric angles with accuracy comparable to conventional methods

Utilizes randomly varying birefringent materials to define a stable polarization orbit

Enables polarization measurements without prior polarization state knowledge

Abstract

We show that, under the right conditions, one can make highly accurate polarization-based measurements without knowing the absolute polarization state of the probing light field. It is shown that light, passed through a randomly varying birefringent material has a well-defined orbit on the Poincare sphere, which we term a generalized polarization state, that is preserved. Changes to the generalized polarization state can then be used in place of the absolute polarization states that make up the generalized state, to measure the change in polarization due to a sample under investigation. We illustrate the usefulness of this analysis approach by demonstrating fiber-based ellipsometry, where the polarization state of the probe light is unknown, and, yet, the ellipsometric angles of the investigated sample ($\Psi$ and $\Delta$) are obtained with an accuracy comparable to that of conventional ellipsometry instruments by measuring changes to the generalized polarization state.