Note: A portable rotating waveplate polarimeter

We describe the construction and performance of a polarimeter based on a quarter-wave plate rotated by a model airplane motor. The motor rotates at a high angular frequency of $ω∼2π×160$ Hz, which enables the polarimeter to monitor the polarization state of an incident beam of light in real-time. We show that a simple analysis of the polarimeter signal using the fast Fourier transform on a standard digital oscilloscope provides an excellent measure of the polarization state for many laboratory applications. The polarimeter is straightforward to construct, portable, and features a high-dynamic range, facilitating a wide range of optics laboratory tasks that require free-space or fiber-based polarization analysis.