6.1 Introduction

In Chapter 5, we examined the Jones vector representation of polarized light, which is quite simple and straightforward. This representation, however, can describe only polarized light. In this chapter, we discuss a more versatile representation of the polarization state of any light wave (completely polarized, unpolarized, or partially polarized), which was first proposed by George Gabriel Stokes in 1852.

6.2 The Stokes Parameters

The representation uses four observable parameters, known as Stokes parameters, which are defined as

(6.1)

In Eq. (6.1), I₀ represents the intensity of the given light beam, and I_H, I_V, I₊₄₅, I_-45, I_RCP, and I_LCP represent the transmitted intensities when the given beam is passed through a linear horizontal polarizer (LHP), a linear vertical polarizer (LVP), a linear +45-deg polarizer, a linear −45-deg polarizer, a rightcircular polarizer, and left-circular polarizer, respectively. Physically, S₁ gives an idea of whether the given SOP is closer to linear horizontally polarized light (S₁ > 0) or to linear vertically polarized light (S₁ < 0) or to neither (S₁ = 0); S₂ gives an idea of whether the given SOP is closer to the linear +45 deg (S₂ > 0), to linear − 45 deg (S₂ < 0), or to neither (S₂ = 0); similarly, S₃ gives an idea of whether the given SOP is closer to right-circular polarized light (S₃ > 0), to left-circular polarized light (S₃ < 0), or to neither (S₃ = 0).