Quantitative measurement of birefringence in transparent films across the visible spectrum

Abstract

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 a 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.

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“…Finally, we estimated the film birefringence by accounting for the proportion of backing material (65.5%) to the whole layer thickness. The estimated birefringence was 0.0012, within the literature value range (0.0007-0.0022) [55,56], while it can vary significantly by environmental factors such as stress and temperature.…”

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“…The birefringence of standard adhesive tapes was evaluated in a recent study 27 . Here, a multi-layered tape made of polyethylene and adhesive (each layer ∼0.05 mm thick) was used to simulate layered structure of biological tissues.…”

“…The birefringence of standard adhesive tapes was evaluated in a recent study. 27 Here, a multi-layered tape made of polyethylene and adhesive (each layer thick) was used to simulate layered structure of biological tissues. The laminated structure will deform under compression, and we used this multi-layered phantom to simulate the impact of structural modifications on polarization [ Fig.…”

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