  Common transparent polymer films such as cellophane and household tape are
frequently used as examples of birefringent materials in textbooks and
classroom demonstrations. Qualitatively, birefringence is often demonstrated by
layering such films between crossed-polarizers. In this work, we describe an
inexpensive experimental setup for the quantitative measurement of
birefringence in common household films, suitable for senior high school or
undergraduate labs. Whereas traditional approaches for polarization-based
classroom experiments typically use monochromatic laser light, we encourage the
combined use of an incoherent incandescent light source and portable
spectrometer. In addition, we demonstrate how any concomitant thin-film
interference effects can be used to separately measure the optical thickness in
the most heterogeneous and uniform films. Such measurement can then be used as
an independent experimental confirmation of either the film's index of
refraction or its thickness, given knowledge of the other. In an effort to
provide examples for the data analysis procedures as well as to investigate a
range of materials, we measure the birefringence across the visible spectrum of
six common household polymer films, including thin kitchen wrap, cellophane,
gift basket film, and common adhesive tapes.
