Precise polarization measurements using polarizing sheets

摘要

We show how to correct polarization measurements performed with non-ideal polarizers. The formulas presented in this note can be used to perform precise polarization measurements using inexpensive polarizing sheets. The simplest method to measure the state of polarization of (completely polarized) light, is using a rotatable polarizer and a photometer, as shown in Figure 1. Specifically, one measures the output intensities along the axes of maximum and minimum polarizer transmission, I-max and I-min. When I-min = 0, one has linearly polarized light; when I-max = I-min, the light is circularly polarized, and, in general, when I-max not equal I-min, the light will be elliptically polarized with ellipticity omega = arctan ([I-min/I-max](1/2)). When the polarizer is not perfect-the polarizing degree of an inexpensive polarizer is not 100%-instead of measuring the projection of the incident field along the transmission direction of the polarizer, what we actually measure is a sum of projections along the transmission direction and its perpendicular, weighted by the respective coefficients. This modifies the measurements sometimes significantly. For example, we could obtain I-min not equal 0 even for linearly polarized light. In this note, we propose a simple device-built with inexpensive polarizing sheets-to determine the state of polarization of light that compensates for the deficiencies introduced by non-ideal polarizers. [References: 2]